There are broad prospects of CO₂ flooding for enhancing oil recovery and greenhouse gas storage. In this paper, we reviewed the development history and brief situation of CO₂ flooding at home and abroad, analyzed the development status of CO₂ immiscible flooding and CO₂ huff and puff, and summarized the phase state of CO₂ flooding, oil displacement mechanism evaluation and optimization design technology of CO₂ flooding reservoir engineering. The design focused on improving oil displacement efficiency and sweep efficiency, controlling viscosity index and gas breakthrough, achieving miscible or near-miscible flooding, and optimizing well pattern and injection parameters in combination with reservoir characteristics. It was pointed out that CO₂ near-miscible flooding and increasing sweep volume were the development trends of CO₂ flooding. WAG, foam flooding, fracture sealing and local gravity flooding were important means to prevent gas channeling. On the basis of summarizing the current CO₂ flooding technology and field experience at home and abroad, the top-level design of combination of CO₂ flooding and CO₂ geological storage should be done according to different types of reservoir characteristics.

Based on the summary of deep shale gas breakthrough wells in recent years, four geological characteristics of deep shale gas are put forward. First, the basic evaluation parameters of deep and shallow shale are similar, but gas content and porosity of deep shale are generally higher than those of medium-deep shale. Second, the horizontal stress difference of deep shale is much greater than that of medium-deep shale. Third, deep shale gas in the basin is generally overpressured, and the pressure coefficient is generally between 1.9 and 2.1, while the complex structure area at the edge of the basin is normally pressured. Fourth, the positive structure is still the main factor for high yield of deep shale gas. Based on the analysis of the decline characteristics of single well production curve in Haynesville and Barnett shale gas fields and the geological characteristics of deep shale gas in Sichuan Basin, three main problems of deep shale gas, namely theoretical understanding innovation, engineering process applicability as well as cost and benefit development. The corresponding countermeasures are also pointed out.

The fractured-vuggy carbonate reservoir is one of the main types of oil and gas reservoirs in Tarim Basin, which has great potential and broad prospect. In recent years, Sinopec Northwest Oilfield Company has continued the exploration and development for them, and has made many breakthroughs in the researches of basic geological theory of carbonate rock, seismic identification technology of fracture cavity body, and high-efficiency development engineering technology. And it has established a series of relatively perfect geological and reservoir engineering methods and technologies for carbonate reservoirs. It has realized the continuous increase of storage and production and efficient development of carbonate reservoir in Tahe oilfield, showing a good prospect of exploration and development, and also providing reference for the exploration and development of similar reservoirs at home and abroad. However, how to develop carbonate fracture-cavity reservoir sustainably also faces the problems and challenges such as theoretical innovation and technological breakthrough. It is urgent to tackle the key problems and make breakthroughs in fracture-cavity structure description, quantitative characterization of remaining oil, utilization of reserves around wells, and heavy oil recovery, so as to continuously promote high-efficiency and high-quality development of carbonate fracture-cavity reservoirs.

With the research and application of the geology-engineering integration technologies, North America has won the victory of shale revolution, and the United States has realized energy independence, playing a dominant role in the global energy market. Its history and experience in shale revolution are the references of great value to the exploration and production of hydrocarbon resources in China. With abundant oil and gas in the exploration areas of Sinopec and various types of favorable targets, accelerating exploration and production is of great significance to improve China's energy structure and ensure national energy security. The application of geology-engineering integration has brought benefit development for the marine shale gas in the Sichuan Basin. In terms of realizing efficient exploration and production of the ultra-deep marine carbonate, tight sandstone and shale, five key studies are suggested to be strengthened: ①fine reservoir description and adaptive fracturing technology of exploration and production for complicated reservoirs, ②ultra-deep carbonate reservoir prediction and optimal drilling technology system, ③application of big data in realizing efficient adjustment and optimize completion program for tight sandstone gas reservoirs, ④development of multi-layer and three-dimensional production technology for marine shale oil and gas, ⑤research on the key problems in the deep, normal-pressure and continental shale oil and gas. To achieve high quality exploration and efficient production of oil and gas, Sinopec will keep strengthening the basic geological research and engineering technology innovation, upgrading technical equipment and following the idea of geology-engineering integration. And then, Sinopec will establish integrated operation coordination mechanism and emphasize integrated management of whole process in order to cut costs and increase efficiency.

With the increasing oil demand in China, it is very important to further tap the potential of oil and gas fields. Chemical flooding technology is one of the important technologies of EOR, and polymer flooding, as the most important method of EOR, has been widely used in the field and achieved good oil displacement effects. Therefore, by summarizing the basic principles of polymer flooding, the development status of various kinds of polymer for oil displacement and the field application effect of polymer flooding, the development direction of polymer flooding in harsh reservoir conditions, such as high temperature and high salt, has been prospected. Through the review, although functional polymers, such as temperature resistant and salt resistant copolymers, instant polymers and amphiphilic polymers, have been successfully developed, the types of polymers used in the field are still limited. How to apply the research and development achievements of new polymers to on-site EOR is the key development direction. With the development of different polymer types, further research on polymer flooding mechanism is needed.

Shale oil reservoir bears heterogeneous pore structure with multi-scale pore sizes. Nano-scale organic intra-granular pore, nano-micro scale inorganic inter-granular pore and micro-fracture coexist in shale oil reservoir. The ultra-low porosity and ultra-low permeability characteristics make the laboratory core flow experiment unavailable for shale oil core sample. As a consequence, shale oil flow parameters in different scale of porous medium can not be measured and it is difficult to accurately evaluate the shale oil flow ability in different scale of porous medium. To solve this problem, a calculation method for pore structure characterization and flow ability of shale oil reservoir is proposed based on digital cores. The nanopore shale oil flow model is first established considering nano-micro scale transport mechanisms and occurrence state, and the influences of shale pore surface physicochemical property and pore size on shale oil flow are analyzed. Then, the nanopore shale oil flow model is further extended to 3D porous media by establishing pore network shale oil flow model. The digital cores in different medium and its pore network are constructed based on the multi-scale shale core imaging data in shale oil reservoir. The multi scale pore structure characteristic and shale oil flow ability are studied in detail on this basis. The analysis results indicate that when the pore radii are less than 5 nm, the shale oil permeability is dependent on adsorbed phase permeability. Inter-granular pore dominates shale oil flow ability. The micro-scale effect on shale oil permeability is very small which can be neglected. The micro scale effect and oil slippage are more obvious in organic pores. However, the contribution of organic pore permeability on total shale oil permeability relies on the connectivity of organic pore structure.

The machine learning is not only an important tool for oil and gas big data analysis, but also a general data-driven analysis method. As an important field with a long history and a large data base, oil and gas exploration and development has a great potential for data mining. The use of big data analysis technology for oil and gas field can help decision makers to conduct investment analysis, risk assessment and production optimization, which brings significant economic benefits. The machine learning method has been tried by the researchers applying to the researches on oil and gas. Nowadays, many application scenarios have been proposed with the development of machine learning algorithms, but general solutions for specific scenario are still divided. So that, we introduces the procedure of a machine learning modeling upon the most basic principles, and summarizes the development history of the main three kinds of machine learning methods that can be applied to oil and gas big data analysis. And then based on the characteristics of oil and gas field big data, the core contents, goals and advantages of oil and gas field big data analysis and utilization are discussed, the main application scenarios of machine learning in oil and gas field are analyzed, and the existing problems and countermeasures in typical oil and gas production prediction are summarized.

Currently, the problem of intra-well frac hit is serious in shale gas, which disturbs the production of nearby wells. Taking the Weiyuan national shale gas demonstration area as the research object, and according to the production characteristics of parent wells, quantitative evaluation index of intra-well frac hit influence based on the recovery rate of parent well production has been put forward. Then ten key geological and engineering parameters affecting intra-well frac hit influence have been analyzed by grey correlation method. The result shows that the grey correlations of intra-well distance, parent well producing time, average fluid volume of single cluster and natural fracture are higher. On this basis, the influence of intra-well position, parent well production time and average fluid volume to intra-well frac hit extent has been evaluated to obtain the following results. Firstly, the main intra-well position of frac hit is parallel, while the secondary is the position of opposite and malposition. Secondly, as the producing time of parent wells increase, the impact of frac hit significantly increases. The suggested optimal operation time of child wells is within 300 produce days of parent wells. Thirdly, as the average fluid volume of single cluster of child wells increases, the impact of frac hit increases too, so that it is suggested to optimize the liquid scale of single cluster according to the production time of parent wells and intra-well position. Lastly, the fluids volume, perforations and slurry rate should be strictly optimized in the section with cut-through natural fracture in order to reduce frac hit risk. Field tests show that the result can provide a reference to reduce the impact of intra-well frac hit of shale gas.

Normal pressure shale gas is one of the main types of shale gas exploration and development in China. It has great resource potential and broad prospects. In recent years, Sinopec East China Oil and Gas Company has continued to carry out normal pressure shale gas exploration and practice in Nanchuan-Wulong area of the basin-margin transition zone in southeastern Chongqing. Positive progress has been made in the following aspects such as basic geological theory research, low cost engineering technology research, green mine construction of normal pressure shale gas. The enrichment and high yield geological theory of “three factors controlling gas”, and the classification and evaluation standard and the target evaluation system of shale reservoirs are established. Six low cost engineering technologies of normal pressure shale gas are proposed, that is, low density 3D seismic exploration, well completion at the “second” section, “drop ball steering+continuous sand addition”, “three steps” fracturing sand addition, electric fracturing and high efficiency drainage gas production. The development technology strategy of normal pressure shale gas is preliminarily formed. The integrated green exploration and development mode is put forward. More breakthrough and efficient development of normal pressure shale gas exploration are realized. Normal pressure shale gas shows a good prospect of exploration and development. However, the exploration and development of normal pressure shale gas in China is still in its infancy and exploration stage. There are still many challenges in aspects such as theoretical innovation, technological breakthrough and benefit development. So that five countermeasures are proposed for the development of China’s normal pressure shale gas industry: ①deepen the research on the main controlling factors of shale gas enrichment and high-yield, and strengthen the target evaluation; ②speed up the research on the supporting technology of excellent drilling and completion for the further acceleration and efficiency increasing; ③strengthen the research on high-efficiency fracturing technology to increase production, reduce cost and increase efficiency; ④strengthen the research on the production rule of normal pressure shale gas, and formulate the technical strategy of benefit development; ⑤fully implement the integrated operation mode of shale gas geological engineering, improve the management quality and create benefit. These countermeasures are counted on accelerating the development of normal pressure shale gas industry in China.

The results of surface porosity obtained by scanning electron microscopy image processing can effectively reflect the development degree of shale organic matter pore. On the premise that the statistical sample is large enough, the pore size of organic matter can be quantitatively characterized relatively accurately. Due to the limitation of absolute resolution of scanning electron microscopy, the organic pore content was underestimated in the pore size range of less than 2 nm. The results of pore size distribution obtained by adsorption method need to be corrected. Combined with TOC and effective porosity, the porosity of shale organic matter can be calculated, and the proportion of organic and inorganic pore can be obtained indirectly. The data of 4 shale gas wells in southeastern Chongqing show that organic pore is the main type in Wulong and Dongsheng area, and the proportion of organic pore in bottom layer（① to ②） is high, up to 85.89 %. Pengshui area is controlled by organic carbon, and the proportion of organic pore is not more than 20 %. The organic pore proportion in Pingqiao area ranges from 20 % to 30 %, and the bedding fissures and laminar structures are relatively developed, especially the possible fissures or grain margin fissures between clastic particles and muddy interbeds in laminar structures contribute greatly to the inorganic pore. The proportion of organic pore is mainly affected by the abundance of organic matter and the degree of pore development of organic matter. The ratio of organic pore is highly consistent with the variation of TOC content in the vertical direction.

Nowadays, the CCUS industry is developing rapidly worldwide, of which the projects are gradually turning from single-section items to whole-industry ones. The target of capture has expanded from power plants and natural gas processing to steel, cement, kerosene, fertilizers and hydrogen production. At present, there are five major ways to drive the industry: government and public funds, national incentive policies, taxation, mandatory emission reduction policies and carbon trading. In China, the CO₂ emitting enterprises are mainly power plants, cement, steel and coal chemicals, accounting for 92 % of the total emissions. According to the concentration, the low concentration CO₂ emission sources are mainly from power plants, cement, steel and refining and chemical industries, that with high concentration are mainly from coal chemical industry, synthetic ammonia and calcium carbide, and that with medium concentration is mainly from the polyethylene industry. The first are the majority, while the latter two are relatively few. Costs of CO₂ sources are comprised of three main parts: capture cost, compression cost and transportation cost, all of which are affected by the scale of capture. Meanwhile, the cost of capture is also related to the concentration of emission source. For the type of high CO₂ concentration, the expense of compression takes the lead in accounting. And capture cost is for the low CO₂ concentration type. As the tolerance of CO₂ cost is lower than source cost for most oilfields, it is necessary to seek ways like technology, policies or markets to fill the gap and promote the sustainable development.

The improvement of experimental technologies of geological evaluation for shale gas is the key factor for the success of shale gas exploration and development in America. The progress in experimental technologies of geological evaluation of shale gas is summarized from three aspects including gas-bearing property, occurrence and fracability of shale. It mainly focuses on the ultramicroscopic organic petrology, formation porosity thermocompression simulation experiment of hydrocarbon generation and expulsion, and the characterization of pore network, which are developed for high thermal maturity marine shale of South China in recent years. The future trends of experimental technologies of geological evaluation for shale gas are discussed. It is proposed that the effectiveness and connectivity of multiscale pore structure, the characterization of organic and inorganic pore in diagenetic evolution, and dynamic evaluation for fracability are the key studying aspects in experimental technologies of geological evaluation of shale gas.

Shale oil resources are rich around the world and have extraordinary exploitation prospects. However, drilling horizontal wells and huge amounts of hydraulic fracturing measures had sharply increased the cost. A large number of experiments and numerical simulations showed that the gas injection could significantly improve the shale oil recovery. Nevertheless, this technique had not been implemented to the practical exploitation of shale oil. Consequently, it was still controversial whether shale oil recovery could be optimized through gas injection or not. By the comparison of the gas displacement experiments of the shale cores, the numerical simulation of shale oil recovery by gas injection and the gas injection pilots in practical fields, it was found that the results from experimental conditions and numerical simulation models were different from those in field pilots. Li Chuanliang insisted that the shale reservoir was consisted of myriad micro-lithologic traps. It was concluded that only if the gas was injected after fracturing, or establishing an orthogonal horizontal well pattern to dense the well spacing, would the shale oil recovery be improved. It has essential guidance for the improvement of shale oil recovery in China or even in the world.

The shale gas fields in Southern Sichuan are developed in an integration mode of testing, production and transmission, which has realized the development goals of cost reduction, emission reduction, fast production commissioning and early returns. However, a lot of empirical practices serve as reference of decision-making during implementation of integration practices. There is a lack of general guidance. In order to study the post-frac soaking, the flowback system and the drainage measures, the experiments of overpressured NMR imbibition, permeability stress sensitivity and gas-liquid two phase percolation are conducted, the flow regime and the distribution of pressure profile are simulated, and the discharge and production effect of more than 30 wells in Southern Sichuan shale gas field has been evaluated. The results show that the entry of fracturing fluids into reservoir through imbibition is beneficial to increasing the complexity of shale cracks, and the optimal shut-in time of Southern Sichuan shale gas field is 4~10 days. Meanwhile, a six-staged flowback system is formed, and a post-frac drainage guide chart is established. It is determined that tubing and manual lifting should be implemented when the flow regime changes and the tube should be installed at the well deviation of 70° ~ 85°. Besides, the drainage strategy is also proposed. In general, the research results are of great significance for guiding post-frac production control and drainage technology.

Climate change centering on carbon dioxide（CO₂） emissions and energy security centering on the shortage of oil resources are two major problems restricting the sustainable development of China's social economy. In order to solve the bottleneck of both the CO₂ capture and the great improvement of recovery factor of low permeability reservoir, the related technology researches have been carried out in Shengli Oilfield, forming the supporting technologies such as CO₂ capture, safe long-distance transmission, reservoir engineering optimization design, the injection-production process design, design of surface gathering and oil displacement and environmental monitoring, and building an industrial-scale demonstration project for flue gas CO₂ capture, oil displacement and underground storage of coal-fired power plants. The industrial tests show that the cost of the new MSA technology is 35 % lower than that of the traditional MEA technology. Over 31×10⁴ t of CO₂ have successfully been injected into the reservoir, with the cumulative oil increment of 8.6×10⁴ t, and 28×10⁴ t of CO₂ storaged in G89-1 block. The central well area has increased the recovery rate by 9.5 %, and the recovery rate is expected to reach 17.2 %.

Efficient development of Zhongjiang gas reservoir is faced with four difficulties: the meticulous channel depiction, the establishment of high-yield enrichment mode, the formulation with development technology policy, and corresponding engineering fracturing technology. For the narrow channel sand bodies, the multi-domain and multi-attribute fine description and accurate reservoir prediction technology are used, and the spatial distribution characteristics of multi-stage and overlapping channel sand bodies are well described. It can depict the channel sand bodies of the thinnest 8 m and the narrowest 50 m, and the sedimentary time sequence of each channel sand body is also very clear. An improved three-parameter pre-stack inversion technique based on ray parameter domain is used to realize the high-precision quantitative prediction of thin-layer, the predicted error of reservoir thickness and porosity is less than 10 %. By establishing an effective combination model of source rock fault and channel sand, with high ancient and modern structures or high ancient and low modern structures, and good reservoir physical properties, it is expected to obtain high and stable production of gas wells in these areas. By using the techniques of 3D deployment of well groups, well pattern optimization and horizontal well optimization design, the production degree of tight sandstone gas reservoir in narrow channel is greatly enhanced, and the investment cast is saved. By using the integrated horizontal well fracturing technology, the single well test gas production is steadily increased, and the transformation effect is increased to 10.6 times before implementation. High-efficiency development technology of tight sandstone gas reservoir formed by narrow channel enables efficient exploration and development of the Zhongjiang Gas Field, the largest gas field of Sinopec in western Sichuan, with an annual gas production of more than 1 billion cubic meters.

According to the classical theories of the oil and gas accumulation, oil and gas are always gathering in the trap of high position. However, the phenomenon of OWC differentiation occurrs occasionally during the actual exploration and development of the oil field. W oilfield located in the concave inversion zone of the middle section in Liaozhong sag of Bohai Sea is a complex fault block reservoir. For the developed wells in the strike slip zone of the oilfield, we analyze the causes of the OWC differentiation. On the basis of the stratification and contrast, the reasons are mainly from the aspects of structure, accumulation and reservoir. It shows that OWC differentiation is due to the poor accumulation condition and sand body superimposition. According to the research on tracking of sand body and deposition characterization, it is considered that Dong-3 segment of this area shows the retrogradation phenomena, while the Dong-2 segment shows the progradation phenomenon. Besides, the Dong-2 segment's sand strata ratio is higher than that of Dong-3 segment. The mudstone of Dong-3 segment is relatively developed with good longitudinal plugging. Meanwhile, the progradation and retrogradation patterns are corresponding to the superposition relation of different sandbody. Then, a difference in oil-water interface appeared.

The study of proppant transport in fractures is of great significance for guiding fracturing design and evaluation. The current researches of proppant placement rules mainly focus on displacement, proppant type, fracturing fluid viscosity, etc. However, there are few studies on the effects of different proppant combinations on proppant transport rules. In this paper, the experimental schemes of the influence of different proppant combinations on proppant transport rules are designed. Then the self-designed visual parallel plate device is used to carry out these experiments. The results show that the distribution of the proppant with smaller particle size is more evenly in the fractures, but the proppant with larger particle size is easier to settle at the wellhead. When medium particle size and large particle size proppant are combined in different proportions, there are small differences in the equilibrium heights of the formed sand bank, but the differences between the non-uniformity of the sand bank height are large. Meanwhile, a large amount of proppant settles at the entrance end of the crack. The proppant filling amount in the deep crack is small, and the effective filling crack with sufficient length and diversion capacity is failure to be formed. When the medium and small particle sizes are combined in different proportions, the proppant can obtain a farther distance than that of the combination of medium particle size and large particle size. The height of the formed sandbank is ideal, and the difference in the non-uniformity of the height of the sand bank between different proportions is also greater.

Pengshui block is a typical shale gas reservoir at atmospheric pressure which has lower coefficient of original formation pressure, and usually needs artificial lift recovery after fracturing. In the initial stage, we optimized the electric submersible pump for the drainage gas recovery. This technology was simple, meanwhile, the formation energy declined gradually, the formation liquid supply gradually decreased and the recovered fluid contained impurities such as sand and clay particle, so that it was hard to realize the stable continuous drainage and recovery, and had complex operation precess and high production cost. In order to solve these problems, we researched and applied the jet pump, and optimized the technology parameters and matching technology. At last, we formed a set of jet pump technology suitable for the drainage gas recovery of shale gas at atmospheric pressure to effectively guide the pressure of shale gas recovery.

Because of the importance of preservation conditions and shale pore evolution to shale gas exploration and development, it is of great scientific significance and academic value to study the relation between them. The pore structure characteristics and evolution of black shale with different preservation conditions have been studied by means such as argon ion polishing, scanning electron microscope and nitrogen adsorption, and it is found that the pore structure of black shale under different preservation conditions are significantly different. This difference is caused by the difference of preservation conditions in the late uplift process, which is manifested in the following aspects. First, inorganic pores in black shale with good or bad preservation conditions are both less developed, and most of the original intergranular pores are filled with generated hydrocarbons. The inorganic pore characteristics between them are basically similar. Second, the organic pores in black shale are of great difference under different preservation conditions. The diameter of shale organic pores is larger in good preservation conditions, which are in round or bubble shape. While the organic pores are relatively smaller in diameter or totally absent in poor preservation condition, which are in flat or irregular shape with the certain characteristics of flattening and deformation. Third, the pore volume and specific surface area of the black shale under good preservation conditions are better than that under poor conditions. Fourth, the porosity evolution of black shale is affected by preservation conditions. The original pore morphology and distribution are controlled by facies and diagenesis process, and so are the organic matter（oil） distribution form. Thermal evolution of organic matter（oil cracking） influences the existence of organic pores. Whereas, in the late uplifting process, the pore structures（shape, size, pore volume） are affected by the quality of the preservation condition. Therefore, the size, morphology and porosity of the shale organic pores reflect the preservation conditions of shale gas in some extent.

Deep shale gas（buried depth is larger than 3 500 m） is the potential resource for future exploration in Sichuan Basin. Although the industrial shale gas flows have been obtained at the depth of 3 500~4 000 m in Wufeng-Longmaxi Formation of Sichuan Basin, the commercial development hasn’t been put into practice due to the rapid decline and the low EUR（Estimated Ultimate Recovery）. Based on the analysis of the current status of shale gas exploration and development, the challenges in the deep shale gas development with high efficiency and large scale in Sichuan Basin have been summarized, mainly in the following aspects: the understanding of occurrence mechanism and enrichment law of deep shale gas needs to be deepened, engineering and technology of economical and effective fracturing treatment need to be established, and the organizational operations and management methods of deep shale gas development are difficult to meet the needs of the large-scale and high efficient development. Three countermeasures are proposed to realize the large-scale and highly efficient development of deep shale gas: ①deepening the understanding of deep shale gas enrichment laws, establishing the methods of area selection and evaluation, and forming the prediction and description technologies of “sweet spot” and “sweet window”; ②deepening the research on the geological conditions of deep shale gas, forming an advanced supporting technology of drilling and fracturing and an equipment system to fully release the reservoir capacity; ③promoting the geology-engineering integration, building a new system and mechanism, and greatly reducing the cost to maximize the development benefits of deep shale gas. The industrial gas flows have been obtained in several wells at the depth of more than 3 500 m of Wufeng-Longmaxi Formation in Sichuan Basin and the proven reserves have been submitted. It is the key and priority stratum of the deep shale gas development. By deepening the geological understanding, overcoming the key technical problems, and improving the management system, it can significantly accelerate the speed, reduce the cost, increase the efficiency and achieve a large-scale and highly efficient development in a relatively short period. The output is expected to be higher than that of the middle and shallow shale gas reservoir.

Due to the deep buried depth（3 500~4 200 m）, high ground stress, high ground stress discrepancy（7 to 17 MPa）, low reservoir brittle（< 0.5） and the undeveloped natural fracture, the hydraulic fracture of Weirong deep shale gas face the problems of high fracturing construction pressure, narrower pressure window, low sensitive sand concentration, high fracturing difficulty. Large-scale physical model experiments show that the morphology of Weirong shale fractures are composed of main fracture and branch fracture, within low fracture complexity and forming bedding seam more easily. On the basis of geology-engineering integration, the stratigraphic segmentation and clustering are optimized in combination with geological sweet spot. Through the study of the proppant transport, the placement mode and injection timing of the three-grade particle size proppant have been optimized, which increase the sand loading. The transverse complexity of fractures is improved by the combined temporary plugging steering fracturing technology. The net pressure and complexity of fractures are improved by the temporary plugging in the fractures and the optimization of construction discharge and liquid viscosity, thereby improving the fracturing volume and control reserves. The research results have been successfully applied in Weirong Gas Field. The sand loading has been increased to 1.95 t/m, the average open flow per well is 38.5×10⁴ m³/d, and the single well EUR is 90×10⁸ m³. All those shows a significantly improvement compared with the previous stage. Post-pressure evaluation shows that the fracturing effect is positively correlated with the sand adding strength. Therefore, how to improve the sand adding strength and control the strength of the liquid used in deep shale gas is the key to economic and effective fracturing.

Since the 1970s, CO₂ flooding-EOR technology has formed multiple development modes in the concept of reservoir engineering, including continuous CO₂ injection, WAG injection with constant proportion, tapered/hybrid WAG injection and SWG/SSWG injection. The reason why CO₂ become the injection gas for tertiary oil recovery with great vitality benefits from its supercritical fluid characteristics and remarkable solvation capacity. Based on the analysis of the main oil displacement mechanism of CO₂ and the reservoir engineering concept and development mode of typical CO₂ flooding-EOR technology at home and abroad in recent years, and considering their development characteristics of different types of reservoirs, especially the successful application of horizontal well technology and low permeability reservoir volume fracturing technology, as well as the comprehensive utilization concept of CO₂ CCUS-EOR combined with CCUS concept, further suggestions are put forward for the development of reservoir engineering development mode by CO₂ flooding-EOR technology in China, so as to provide enlightenment for further promoting its large-scale development.

In order to guarantee the fast and professional solution about types of water production and mechanism of water invasion in the Rumaila complex multilayer carbonate reservoir of Ahdeb oilfield with casing channeling, high permeability zone and situation of commingled production, a fine reservoir model which can characterize the pure aquifer zone, oil-water transition zone and pure oil zone was built. On this basis, combined with analysis of water invasion velocity in each reservoir, the various simulation curves would be calibrated by the actual typical production curves to obtain the different typical water control diagnostic plots including casing channeling with bottom aquifer coning, bottom aquifer coning with later casing channeling, single casing channeling and the section of perforation located in the oil-water transition zone with later casing channeling（including different position of casing channeling: pure aquifer zone, oil-water transition zone and pure oil zone） with dimensionless time, which would be used to distinguish and analyze the reservoir water-producing type and rules. The results showed that the water control diagnostic plots could accurately obtain the water production type and rules, decrease the downhole PLT, SWFL and other tests, and provide reliable basis for the stabilizing oil and controlling water of vertical wells.

In shale gas reservoirs with natural fractures, the artificial fractures and natural fractures communicate with each other after fracturing. The traditional dual media model can not accurately reflect the impact of natural fractures on well production. In order to investigate the influence on shale gas well productivity caused by gas transport in nanometer-size pores, the mathematical model of multi-stage fractured horizontal well in shale gas reservoir is built, which considers the influence of the complex flow mechanism such as the viscous flow, Knudsen diffusion, surface diffusion, adsorption layerand gas desorption. Discrete fracture model（DFM） is used to simplify the fracture and finite element method is applied to solve the model. The numerical simulation results of Pingqiao shale gas reservoir indicate that the free gas in fracture system mainly contributes to shale gas production in the early stage, and the average recovery of adsorbed gas is only 10.1 %. The existence of unmodified reservoir makes the influence of bedrock permeability on cumulative production greater. The density and connectivity of fracture networks have dominant effects on gas production and its decline trend.

The capillary bundle model is one of the most common physical models for the porous media. The most classic physical model is the straight capillary bundle model with same diameter. But the bendability of the porous media is neglected in this physical model. Therefore, based on the tight sandstone, combined with the mercury data, and by the introduction of the correction factor-tortuosity, we put forward a new approach to establish the capillary bundle model. This approach considers the bendability of the capillary bundle model and can accurately calculate the radius of capillary, capillary porosity and permeability, capillary volume of different radius and permeability contribution of capillary bundle model with different radius. This new approach has great significance for the study of the reservoir fluid imbibition of specific pressure and quantitatively characterizing the water invasion reservoir damage.

In view of the technical difficulties of CO₂ flooding completion string, the research process and development situation of completion string of CO₂ flooding injection-production well were systematically expounded. It was concluded that the sealing performance of the completion string of injection well and anti corrosion and gas proof performance of production well were the key technologies for the normal production of CO₂ flooding injection-production well. The pilot test of CO₂ flooding in domestic oilfield showed that the continuous optimization of packer and the gas tightness detection of tubing contributed to improve sealing of injection wells, and the technologies like CO₂ corrosion inhibitor formulation, injection strengthening, tube controlling by gas lifting, downhole oil and gas separation were helpful to improve the pumping efficiency of the production wells. Meanwhile, in view of the technical problems faced by the injection and production wells on site, the further research direction of production by CO₂ flooding injection and production technology was pointed out.

CBM development in China focuses on the high-rank coal, which is brittle and, during drilling, fracturing and drainage, easily crushed into coal fine. During the production, coal fine flows owing to the water flashing effect. As the water production declines, the coal fine will sediment and block the flowing channels, leading to the great reduction of coal permeability. When the coal fine enter the wellbore, it may jam the pump, resulting in accidents in production such as pump stuck or buried pump, and leading to the stop of production for well repair. In order to solve this problems, the generation mechanism, migration rules and current major controlling approaches of coal fine are summarized. And then, the mechanics model, hydraulic model and migration model are investigated respectively. According to the former studies, the coal fine migration process can be summarized as four stages: denudation, detachment, suspension and sedimentation. However, the geology conditions of coal seam in China are extremely complex and the structure changes effect is dramatic on coal basins. These factors enhance the problems of production and migration. Nevertheless, the coal fine controlling approach method primarily learns from the sanding control technology in oil reservoir and is still undeveloped for the CBM reservoirs.

Experiments for seepage flow patterns in thin and poor reservoirs could be carried out by the plate models made by artificial core designed based on the similarity theory. Pressure gradient distribution in fractured thin and poor reservoir by fine controlling was revealed based on the pressure data, and the sketch maps of seepage flow sections were drew to study on seepage flow patterns of fine controlled fractured thin and poor reservoir qualitatively and quantitatively. Experiment results showed that seepage flow patterns in thin and poor reservoirs were greatly influenced by permeability, heterogeneity and fine controlled fracturing cracks while the thin and poor reservoirs had low permeability and strong homogeneity. Fine controlled fracturing could reduce the negative influence of low permeability and strong heterogeneity. Thin and poor reservoirs could be divided into the non seepage flow section, the nonlinear seepage flow section and the quasi linear seepage flow section. The non seepage flow section was reduced by over 72 % after fine controlled fracturing, the area for fluid flowing through increased correspondingly, and the proportion of quasi linear percolation area which was more conducive to fluid flow raised by at least 86 %.

A trilinear flow model is one of the common methods solving the well test models for the multistage fractured horizontal wells. By the orthogonal test, the range analysis method and the variance analysis method, we analyzed the influence of the half fracture length, the half reservoir thickness, the width of the inner zone, the dimensionless fracture conductivity and the permeability in inner zone on the double log curves fitting of the pressure and the pressure derivative of the trilinear flow model and numerical model. According to this analysis, the factors affecting the curves of the pressure characteristic curves of two models ranged from more to less are the dimensionless fracture conductivity(F_CD), the permeability in inner zone(k_I), the half fracture length(x_f), the half reservoir thickness(x_e)and the width of inner zone(y_e). The fracture conductivity affect obviously on the fitting of the pressure characteristic curves of two models. When the fracture conductivity is less than 1, the curve fitting effect is poor, so the linear flow model is not applicable. Otherwise, when the fracture conductivity is greater than 1, the curve fitting effect is good, so the linear flow model is suitable.

CO₂ flooding is a promising way to improve the crude oil recovery ratio. CO₂ could not only dissolve in crude oil, but also replace some light hydrocarbons or intermediate hydrocarbons in crude oil. So the composition has great influence on the component mass transfer and minimum miscible pressure of the CO₂ miscible flooding. Therefore, the influence of the quantitative characterization of crude oil composition on the minimum miscible pressure of the CO₂ miscible flooding has engineering significance for the reservoir screening. Taking the original formation fluid of a certain oilfield in China as the research object, we analyzed the multistage contact miscibility mechanism. Meanwhile, we used the Winprop module in CMG to carried out the phase simulation of experimental data. The results show that the minimum miscible pressure between CO₂ and crude oil is proportional to the molar composition of N₂, C₁ and C₁₁₊, and inversely proportional to that of C₂~C₁₀. While the mixing of the CO₂ and reservoir fluids needs higher reservoir pressure than minimum miscible pressure. It requires that when screening reservoirs with CO₂ flooding, we should try to consider the reservoir with high mole content of C₂ ~ C₁₀ and low mole content of C₂₄. It has great guiding significance for miscible displacement design and miscible phase prediction.

CO₂ flooding is effective for enhancing the oil recovery in low permeability reservoir and reducing the greenhouse gas emissions. In order to solve the technical problems of difficult miscible phase, easy gas channelling and low sweep coefficient for CO₂ flooding in low permeability reservoir in Shengli Oilfield. By the combination of physical and numerical simulation, the development mechanism of the CO₂ injection miscible flooding long in advance is clarified, and the comprehensive techniques for extra low permeability reservoir is formed. After field application, the stimulation effect is obvious, the daily production of oil per well increase by 5 times. The principle and technical idea of reducing the miscibility pressure are put forward, and the system of reducing the miscible pressure system is developed, which can make the pressure decrease by up to 22 %. The challenge and countermeasure faced by scale application of CO₂ flooding in Shengli Oilfield are analyzed, and the development directions of CO₂ flooding are proposed, such as deepening the phase state theory of oil recovery enhanced by CO₂ flooding, developing CO₂ flooding technology with expanded sweep volume at low cost, developing incomplete CO₂ miscible flooding, and description and early warning of gas channeling. All these provide technical support for oil field to realize scale application of CO₂ flooding.

Nanchuan Shale Gas Field is China's first commercially developed shale gas field dominated by normal pressure shale gas. In order to evaluate the exploration and development prospects of this type of shale gas, the exploration and development history of this area has been reviewed, the geological characteristics of the gas field are analyzed from the aspects such as structure, deposition, reservoir, preservation, in-situ stress, gas reservoir and production characteristics, and finally, the key technologies of exploration and development are summarized. The results show that: ①Nanchuan Shale Gas Field has experienced multi-stage tectonic movement. Its shale gas geological conditions are complex, and there are three structural belts: Pingqiao, Dongsheng and Yangchungou. The characteristics of deposition, reservoir, preservation and in-situ stress are quite different in different tectonic zones, but the shale gas reservoirs are generally with the type of elastic gas drive, mid-deep to deep layer, normal temperature, high pressure to normal pressure and dry gas. ②As for the production, its has the characteristics of high initial test output, high liquid volume, fast decline, medium elastic yield and relatively low single well's EUR. ③Six key technologies of exploration and development have been formed, which are, “sweet spot” target evaluation, reservoir characterization, in-situ stress field prediction, geology-engineering integration design of horizontal wells, development technology policy and low-cost engineering technology. ④The discovery of Nanchuan shale gas field brings four inspiration: firstly, firming exploration confidence is the foundation of exploration breakthrough; secondly, deepening basic geological research is the core of breakthrough; thirdly, innovative technological practice is the key to benefit development; fourthly, the implementation of the integration model is the guarantee of improving quality and efficiency.

Based on the massive analytical data of core, we comprehensively researched on the main controlling factors of the tight oil reservoir according to the property and the storage space of the tight oil formation in Chang-8 reservoir of Fu County in Ordos Basin. Fine sandstone in Chang-8 reservoir contained the movable tight oil with low density and low viscosity, and mostly concentrated in micron-sized pore throats. The accumulation of tight oil was mainly controlled by three factors that were the source rocks of Chang-7 and Chang-9 reservoirs, the main accumulation mode of "the reservoir existed in the resource, and the resource existed in the reservoir", and the high quality reservoir with composite superimposed sedimentary sand body formed in the underwater distributary channel microfacies environment. Based on the controlling factors above, and combined with the current exploration results, we predicted 6 potential blocks of Chang-8 tight oil reservoir in Fu County, and provided the basis for the further exploration.

In general, complex fracture network was formed after SRV fracturing operation in tight reservoirs, and the horizontal well yield was increased by changing the seepage field near the fracturing wells. At present, there was few weight analysis about the influence of SRV fracturing influence parameters of tight reservoirs on fracturing effect at different periods after the production of horizontal wells. By establishing the two-phase finite element equation which was applicable to the tight oil reservoir and water, finite element numerical simulation of complex fracture network was carried out, and the orthogonal experiment and grey correlation method were adopted to analyze the influence degree of horizontal well volume fracturing influence parameters on productivity of oil wells within 10 years. The results showed that the fracture conductivity determines the initial fracturing productivity of horizontal wells, and the fracture length determined the decline rate of daily production of horizontal wells and the level of steady production in the later stage. With the continuous production of fracturing wells, the fracture length replaced the fracture conductivity and became a key factor affecting the yield. The research on the influence degree of each influence parameter on the fracturing effect in different periods in which horizontal wells could provide theoretical support for the construction and design of SRV fracturing horizontal wells in tight reservoirs.

As a new field of unconventional natural gas exploration and development, deep coalbed methane（CBM） has great resource potential, but its benefit development faces great challenges. How to carry out efficient development is a problem needed to be solved at present. In order to achieve stable production and steadily promote the expansion of the gas field, focusing on how to realize the problem of “long fracture and far support” in reservoir reconstruction, Yanchuannan gas field has achieved good results through fracturing optimization and tackling key problems of deep coalbed methane geology-engineering integration. The research shows that: ①Deep CBM has great resource potential with a high gas content of 13~20 m ³/t, but it is difficult to develop and transform the reservoir and the daily production of single well is low, only of 0~500 m³/d; ②According to the underground observation, in the existing active hydraulic fracturing technology, the effective supporting seams mainly distributes within eight meters of the wellbore, and the main fracture extension is generally less than 30 m; ③Deep coal seam fracturing should take the large-scale artificial fracture with long-distance support and high conductivity as the main target to improve the sand adding strength with large displacement, and at the same time develope “low density and long migration” proppant. The average daily gas production of single well is 1 800 m ³. It provides a new idea for the deep CBM development.

The produced GOR is a key index for the development and design of gas flooding reservoirs. On the basis of confirming that there are five sources of gas production in the whole life cycle of gas flooding, the prediction formula of produced GOR in low permeability reservoirs matching with three development stages is proposed. From gas injection to pre-gas production, the produced GOR is mainly controlled by the initial dissolved GOR of the reservoir fluid, and method of determining the equivalent GOR of water-soluble gas is given. The produced GOR in the stage from pre-gas production to gas channeling is affected by the gas dissolved capacity of ″oil bank″. The method of describing the physical property of gas flooding″oil bank″ in low permeability reservoirs can be used for reference to determine dissolved GOR of gas flooding″oil bank″. The change of produced GOR after gas channeling is determined by the GOR formed by free gas, and its prediction based on the understanding that the pore space released by the produced liquids would be filled with the injected gas and water. It is calculated by oil and gas fractional flow equation, Corey's model and Stone's equation combined with concepts of gas flooding increasing multiple in low permeability reservoir, and slug size ratio of water-gas during water alternating gas injection. The reservoir engineering method of produced GOR prediction taking the form of ″three-stages″ has been verified by the field test of CO₂ miscible flooding. It can be used in gas injection development planning design, optimization of oil production process or gas injection storage potential evaluation.

The Chang 6₁ reservoir was the main oil-bearing beds in the study area of Ganguyi Oilfield in Ordos Basin. The exploration and development practice showed that the reservoir characteristics had strong heterogeneity in three-dimensional space, and the vertical and horizontal distribution of the reservoirs were complex, which directly restrictsed the subsequent rolling exploration and development. In the study, based on the core observations and logging data, and combined with analytical testing, the controlling effect of the reservoir macroscopic heterogeneity on the oil layer distribution was systematically and visually analyzed. The complexity of the Chang 6₁ reservoir in the study area was caused by a variety of factors. Among them, the distribution of the sedimentary microfacies and diagenetic facies directly controlled that of the high quality reservoirs. And the interlayer heterogeneity, especially the interlayer permeability, was easy to cause the selective filling of oil, while the interlayer heterogeneity directly caused the heterogeneous distribution of oil in composite sand body. Through this study, the distribution law of ultra-low permeability and ultra-low permeability reservoirs in Ordos Basin could be better understood intuitively, which provides guidance for finding favorable zones in the future.

The calculation of the bottom hole pressure(BHP) in the high temperature and high pressure the gas wells with should consider the temperature changes inside the wellbore. The coupling of the pressure and temperature need to be solved simultaneously. The current calculation methods considering the wellbore heat transfer, and the coupling of pressure and temperature mainly apply to the steady flow. However, they don’t apply to the transition flow during the shut-in period. Meanwhile, the wellbore heat transmission of the offshore gas well in high temperature and high pressure should consider the effects of sea water. Nevertheless, there are fewer examples of this research. According to the problems above and based on the basic equation, we established a new calculation model, which considers wellbore storage, and the heat transfer among the wellbore, adjacent formation and sea water. This method is successfully applied to the BHP calculation and well testing analysis for the well M1 during the shut-in period in M gas field of the western South China Sea, thus providing the basis for the temperature and pressure calculation and well testing optimization of high temperature and high pressure offshore gas well.

In order to explore the characteristics of rich accumulation and the exploration potential of transitional shale gas, the lower Carboniferous shale in southern Guizhou is taken as the research object. Based on the data of two investigation wells and two exploration wells, the analysis is conducted from the aspects of stratigraphic sequence and sedimentary facies, occurrence characteristics of shale, accumulation conditions and favorable area evaluation. The research result shows that: ① The lower Carboniferous shale deposits in western Guizhou are controlled by the NW-SE Shuicheng-Ziyun synsedimentary fault and the Shuicheng-Liuzhi uplift partition, which can be divided into weining shuicheng tidal flat lagoon-transition sedimentary facies and Shuicheng-Ziyun shallow-water shelf marine sedimentary facies, forming Weining and Ziyun depositional central areas with deposition thickness ranging from 30 m to 200 m. The sedimentary thickness of Weining-Shuicheng is 119 m, and the embedded depth of floor is between 1 500 m and 3 000 m, which is a favorable area for exploration. ② Influenced by multi-stage structure and controlled by syndeposition, the gas accumulation type controlled by the combination of folds and faults is relatively developed in this area, which is a typical gas accumulation mode controlled by the structure of anticlinal combination blocked by reverse fault. ③ On the plane, the accumulation zone of Weishui anticline and Shuicheng-Ziyun fault structure is a favorable exploration area for shale gas research in Weining-Shuicheng, the sedimentary center of Jiusi Formation, with an area of about 944 km². There are at least three sets of organic-rich shale gas bearing beds vertically in the shale, which have good exploration potential

The relative permeability curves of polymer flooding are important bases for the development index predicting the polymer flooding oilfield. Aiming at the low numerical simulation accuracy caused by the lack of the relative permeability of the polymer flooding in the offshore L oilfield, we determined the relative permeability curves of the polymer flooding by the non-steady-state method to compare the relative permeability of different core permeability and polymer concentration. The variation law of relative permeability curve of the polymer flooding was summarized as well. The experimental results showed that the permeability curves of the polymer flooding increased with the core permeability, the relative permeability of the oil phase decreased with the same water saturation, and the residual oil saturation also decreased. With the increase of the polymer concentration, the oil relative permeability of the same water saturation increased, but the residual oil saturation decreased. In the early stage of polymer flooding, the residual oil saturation decreased rapidly, while in the middle and late stages, the residual oil saturation decreased slowly. The research results provided guidance and basis for fine numerical simulation and development planning in offshore polymer flooding fields.

Compared with the single well development mode of the conventional gas reservoirs, multi-well pad technology has several advantages such as great improvement of operating efficiency and reduction of project cost. Strong interference between the wells and between the fractures exist in small well spacing and network fracturing mode of multi-well pad for shale reservoir, which affect the overall development effect of the well group. Based on the unstructured PEBI grid technology, its simulator for fracturing horizontal wells is developed independently. According to the results of microseismic monitoring, the stimulated reservoir volume（SRV） area formed by the network fracturing of horizontal well groups are assumed to be ovals. Considering the adsorption, desorption, diffusion and nonlinear seepage mechanisms of shale gas, the numerical simulation model of the fracturing horizontal well group in the multi-well pad mode is established by the finite element method. The difference between the cumulative production of the single well and the well group is compared, and the influence of the layout mode of the fractures and the horizontal wells on the cumulative production in homogeneous shale gas reservoirs are discussed. The results show that the inter-well seepage interference makes the cumulative production of the well group lower than the sum of that of a single well. U-shape layout mode of the fractures for single well can reduce the interference to a certain extent, which make the cumulative production of the well group superior to that of the uniform mode and the inverted U-shape mode. The cumulative production of cross distribution of horizontal wells is better than that of parallel mode.

Carbonate palaeo-subterranean river reservoirs are fractured-vuggy reservoirs composed of deep main rivers, shallow branch and high-angle fractures, with large-scale karst caves as the storage space, belonging to the three main reservoir types in Tahe oilfield. Taking the knowledge of remaining oil and tapping potential in TK440 well area as an example, through the fine characterization of the fracture-cave structure, comprehensive analysis of production dynamics, and systematic analysis of water flooding characteristics, four patterns of remaining oil distribution and feasible potential tapping methods are summarized..The results show that: using large pump for the well drainage and changing the distribution of pressure field, can excavated the remaining oil in shallow underground river. Water flooding in reverse direction, with the advantage of the height difference, can effectively excavate the remaining oil in deep underground river. Based on the difference of oil and gas density, the vertical displacement of artificial gas cap formed of the principle of gravity differentiation can effectively recovery the attic oil around single well and the remaining oil in the blind side of underground rivers. Feasible means of potential tapping under different distribution patterns of remaining oil has been found, and good results have been achieved in the field implementation, which further validates the reliability of remaining oil distribution patterns and the effectiveness of tapping the potential of the reservoir, and provides technical support for the effectively potential tapping of remaining oil in the similar reservoir.

The commonly used water flooding characteristic curves are suitable in describing the water flooding laws in the middle-high water cut periods. However, these curves can hardly describe the water flooding characteristics of low and high water cut periods because of their theoretical basis of exponential expression of relative permeability curves and approximation during the derivation process. The applications showed that, for different reservoir characteristics and the water cut rising features, the conventional water flooding curves mighe shew as no straight line in the low water cut period and raise in the high water cut period, which resulted in poor fitting effect. So we proposed a new type of water flooding characteristic curve based on a new kind of widely applicable expression of relative permeability curve. This new curve could accurately describe the production dynamic rules under different water cut stages and directly calculate the recoverable reserves by fitting parameters. Applications showed that, by this method, the fitting straight line appeard earlier, the correlation coefficient was high, and the fitting effect was good. It had good applicability in different water cut stages, could describe the characteristics of water flooding more accurately and could easily predict the recoverable reserves. There was good application value in the dynamic analysis and making the production strategy of oil fields.

The conductivity of acid cracks was the key to the transformation effects of acid fracturing. Due to the influences of rock properties, etching morphology and closing pressure, it was difficult to accurately predict the conductivity of acid fractures. Currently, there were many computational models for acid fractures geometry and acid penetration distance, but there were few researches on the computational model of flow capacity. For this reason, we built the acid fracturing model of cracks based on the improved self-affine fractal theory and applied it to the fractal fractures. And then, by the local cubic law（LCL）, we built the acid fracture conductivity calculation model and applied the quadrature analysis to the main factors which affected the conductivity of the acid fracture after closure. The results showed that the influencing degree of those factors which affected the acid fracture conductivity were as follows: closure stress>fractal dimension>injection time>matrix permeability>injection rate>standard deviation>matrix porosity.

The oil and gas well data collection system has been widely used in the shale gas well testing. In the process of operation and management of data collection equipments, the sorting and recording of field data, reporting of field real-time and staged production reports all required to be operated by professional technicians. This work took a lot of time and was error-prone. Automatic report management was a technology combining the actual production of shale gas with the data collection system. Relay on Python, the computer programming language, we could obtain the field data and records, and on this base, compiled and sent reports. This technology can greatly improve the accuracy and efficiency of data recording, and reduce the labor intensity of technicians.

Based on several geological problems in the exploration and development of the normal pressure shale gas reservoir, its classification is explored. For that, the relation between the change of organic carbon content, the degree of thermal evolution and porosity in shale are analyzed. On this basis, the relation between gas content and these geological factors, and between the gas content and initial production are further studied. At the same time, compared with the typical shale gas reservoirs at home and abroad, the controlling effect of shale gas migration with different pressure gradients on the initial production of gas reservoirs is discussed. It is clearly pointed out that there are differences in the energy supply for shale gas migration between transitional normal pressure shale gas reservoir at the margin of （or in） the basin and residual normal pressure shale gas reservoir outside the basin. Although there exists loss, because of the large distribution area of shale in the basin and the sufficient migration and replenishment of shale gas, the transitional normal pressure gas reservoirs at the margin of （or in） the basin have higher initial production and better commercial benefit. While for the residual normal pressure gas reservoirs outside the basin, as they have limited shale distribution area and insufficient migration replenishment, they belong to low pressure reservoir and have low initial production. In order to realize the commercial development, it is necessary to make more breakthroughs in the technologies of increasing production and reducing cost.

In the fractured-vuggy reservoir unit, the water injection mainly affects the oil well unidirectionally and is easy to advance rapidly along the main channel, leading to the problems of difficult to effective control the water drive reserves and low efficient production. By the methods of physical model and numerical simulation, the relation between the structure of fracture/cave and the development effect of water flooding in different karst background is analyzed, and the differential injection-production relation based on the spatial distribution of fracture/cave is formed. The results show that: in the crust karst reservoirs, the mode of water injection in the low part and oil production in the high part of the structure, and water injection in the undeveloped area and oil production in the developed area is adopted to establish the injection-production relation of one injection well to multiple production wells. In the fracture-controlled reservoirs, the mode of water injection in the secondary fault and oil production in the main fault, and water injection in the deep fracture area and shallow for oil production in the longitudinal direction is adopted to form the stereoscopic injection-production relation. In the ancient underground river reservoirs, the water injection in the main section and oil production in the branch are implemented in the main dark section, and the water injection in deep and oil production in shallow are implemented in multiple dark rivers, so as to establish the layered injection-production relation. The establishment of injection-production relation in different karst backgrounds of fractured-vuggy reservoirs lay an important foundation for maximizing water drive controlled reserves of spatial well pattern.

Hydraulic fracturing is an important technical means for stimulation and transformation of oil and gas reservoirs, and has been widely used in the production of major oil fields at home and abroad. After studying a large number of literature research on the fracturing fluid system, it is found that various improvements of the current fracturing fluid system are mainly around “carrying sand”. However, in this paper, a new type of self-supporting fracturing fluid system is innovatively put forward, which completely gets rid of the concept of "carrying sand". In the process of fracturing fluid pumping, there is no solid proppant at all, but the fracturing fluid is combined with the proppant as a whole. When the fluid reaches the target layer, it is affected by the formation temperature and transformed from liquid phase to solid-state to prop up the fracturing fractures. The obtained self-supporting fracturing fluid system can form supporting solids with certain sphericity and strength at 85 ℃ and in 30 minutes. The upper limit of liquid system viscosity is 45.58 mPa·s, bringing the system good injectivity and stability. The density of the solid-state proppant is 1.07 g/cm³, the separation coefficient is 1.41, the main particle size range is 20~40 and 40~70 mesh, and the crushing rate is 4.7 % and 8.75 %, respectively.

Staged fracturing for horizontal wells is one of the key technologies for shale gas development. As the shale gas development in China extends to normal pressure fields, it is urgent to enhance the speed and efficiency of fracturing technology. The existing plug and perf operation technology has many limitations, including long duration of pumping, easiness to stuck tools, limited number of fracturing stages for ball-actuated sliding sleeves, and limited fracturing scale for packers dragged by coiled tubing. For the new infinite stage and full-bore sliding sleeve fracturing technology, the structure principle of the sliding sleeve as well as its technological characteristics are explained, and a pilot test has been carried out in 16 fracturing stages of two wells in Nanchuan Shale Gas Field. This technology replaces perforation and coiled tubing drilling plugs by preset sliding sleeves. All the sliding sleeves are opened successfully. The number of fracturing stages is unlimited and the operation is continuous. The average time of single stage fracturing is 3.5 h and it can finish seven fracturing stages per day. As a fast, safe and efficient staged fracturing technology, it provides a new technical means for enhancing speed and efficiency of fracturing technology for shale gas wells in China.