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.

Based on geological, logging and experimental analysis data, normal-pressure shale gas reservoir of Upper Ordovician Wufeng Formation to Lower Silurian Longmaxi Member in Pengshui area has been researched by the established quantitative characterization method, and it is found that the reserving space of high-quality shale in ①—⑤ layers is mainly composed of organic pores and bedding joints. The arithmetic average aperture measured by FIB nanotechnology with higher resolution ranges is from 20 to 50 nm, being mainly mesopores. However, the volume weighted average aperture is 100 nm, being macropore. In terms of the measured pore volume, macropore is the main contributor to total volume and porosity. Core-scale fractures lead to the abrupt decrease or increase of gas logging and the migration of shale gas at layer-level. The new method, Maps, show that the bedding joints in layer① of well-Longye-1 are open and continuous with an opening width of 4.69 μm, and the opening width of bedding shear joint is 1.1~2.67 μm. The sum of plane porosity for bedding and bedding shear joints is 1.39 %, which accounts for about 1/3 of the total porosity of the sample. It confirms the important contribution of bedding fracture and natural tectonic fracture for shale gas reservoir spaces. Comparing with the overpressure shale gas reservoirs, the porosity of shale reservoir in normal-pressure area is slightly low, and the high-angle seam and bedding joints are more developed. A new parameters and criteria method for evaluating normal-pressure shale gas reservoirs has been established. By this method, favorable reservoir area of type I reservoir is of 620.22 km² in layer ① to ⑤ of Wulong syncline.

Taking well-X, a typical core well of the Wufeng-Longmaxi Formation in Southern Sichuan Basin, as an example, based on core observation, geochemical analysis, X-ray diffraction, physical properties testing, argon ion polishing SEM, hydrocarbon generation simulation and other testing methods, and by using the research idea of “source-storage coupling”, the properties of the core segment as the “source” and the “storage” respectively are analyzed, and the mechanism of “source-storage coupling” is further discussed. The research results show that the bottom shale in Wufeng-Longmaxi Formation is characterized by sapmpelic kerogen, abundant organic matter, and high degree of thermal evolution, in which dry gas mainly generate. The average porosity of matrix is 6.5 %, mainly are inorganic pores. The inorganic pore types are mainly intergranular pore, clay mineral pore, feldspar alteration pore and pyrite intergranular pore. The average amount of adsorbed gas under formation temperature and pressure conditions is 0.9 m³/t. The average permeability is 0.38×10^-3 μm², which means it belongs to an ultra-low permeability reservoir. Generally speaking, the well-X has sufficient “source” at the bottom of the Wufeng-Longmaxi Formation with large amount of generated gas. The current stagnant gas volume is only about 54.8 % of the amount of generated gas, and the matrix pores are mainly inorganic pores. Meanwhile, organic pores are an important supplement. Free gas is the main body. The development of organic-rich shale section improves the permeability of the reservoir. At the same time, the biogenic siliceous minerals enhance the brittleness of the reservoir and make the reservoir easy to be fractured. Therefore, the organic-rich shale section is the best source-storage coupling interval, and also is the main interval of shale gas exploration and development and the key target layer of a horizontal well.

The development of high-quality shale in Wufeng-Longmaxi formation in Wulong area is characterized by wide distribution, large thickness, moderate burial depth, high organic matter abundance and moderate thermal evolution. It is a favorable shale gas exploration area. Due to the typical southern China’s mountainous landform in Wulong and the influence of large obstacles such as Wujiang river and nearby towns, the explosive source is limited, resulting in the emergence of the so-called “data skylight”. The advantages of seismic wave generated by the spark source, such as the rich high-frequency information, good waveform repeatability, good time consistency, safe and free from contamination, meet the source requirements for seismic exploration in the Wulong area. After the application of spark source, the coverage fold of large obstacle area increases and the section gap decreases. The energy of the spark source is 200 ~ 800 kJ, which is equivalent to the energy of the 2 ~ 4 kg well gun（14 kg, 21 m）. A high quality reflection signal can be seen above 2 s of the single shot record, and the effective frequency band is up to 80 Hz. The spark source can effectively make up for the “data skylight” in Wulong and Tukan town, and meet the requirements of 3D geological exploration.

3D seismic exploration technology with the mode of “Wide-azimuth, high-density and broadband” is widely used in the exploration of conventional and unconventional oil and gas. Technical effectiveness and economy are the two main factors restricting seismic exploration, especially unconventional oil and gas exploration（shale oil and gas, coalbed methane, etc.）, whose economy is the main influencing factor. Taking 3D seismic exploration for the shale gas with normal pressure in Wulong as an example, the successful 3D method of shale gas with low density and economy is introduced, and the purpose of reducing the exploration cost of 3D seismic data and improving the exploration effect is achieved. Combined with the similar conventional 3D seismic exploration examples in Taozidang area, the S/N ratio is evaluated and analyzed emphatically. It is pointed out that the application geological background with relatively simple structure, regional enrichment and strong reflective seismic interface, low density observation system with high cost performance, single shot record with high energy and SNR, and methods of improving S/N ratio and high-precision static correction for seismic exploration are the keys to the success of low density 3D shale gas. The application of deep well and large dosage saturation excitation to ensure the energy and S/N ratio of seismic acquisition data, improve the ratio of effective seismic record ratio, and the method and measure of field management are worthy of reference. Its successful experience has been widely used in 3D seismic exploration in Guihua and Yangchungou.

Calculation of 4 parameters, ρ₀, m, τ and c, of Cole-Cole model by complex rock core resistivity data measured with multi-frequency is an important nonlinear optimization problem in rock core complex resistivity experiments. However, in Jiaoshiba Zone, a very small τ and c with big value range cause the difficulty of the convergence of optimization program. Therefore, the initial value determination and optimized iteration step have been studied. The improved program performances well on the speed of convergence, and avoids the calculation failure caused by out-range of the parameter τ. The study indicates that according to the maximum property and asymmetry property, the parameter τ can be obtained directly, and good iteration initial values of the rest 3 parameters can be obtained either. Meanwhile, by transforming the error function to be Tyler series, the optimized iteration step can be obtained and the convergence speed can be upgraded significantly.

The physical and mechanical properties of bedding shales show strong anisotropy, which leads to the significant difference in the logging response of the same formation between the vertical wells and the horizontal wells, and bringing the difficulties in regional reservoir evaluation. Based on the numerical simulations, the influence of orientation and density of bedding on the anisotropy of longitudinal wave has been analyzed, and a correction model for longitudinal wave of shale in Longmaxi formation has been built. Then, combined with the indoor compression wave experiment, the rationality of this new model has been analyzed. The results show that, the longitudinal wave anisotropy of shales in Longmaxi formation is obvious, and the coefficient of longitudinal wave is around 1.088 ~ 1.109. The coefficient of longitudinal wave anisotropy has a quadratic polynomial relation with the sine of the bedding angle, and the anisotropic coefficient increases linearly with the increase of bedding density. Application examples show that this new model can reasonably correct the acoustic response of horizontal wells to that of vertical wells.

The joints in the stratum have a greater impact on the formation of complex fracture networks with hydraulic fractures. In order to study the propagation behavior of hydraulic fractures when they encounter orthogonal joints, the hydraulic fracturing of 3D orthogonal fractures is simulated based on the discrete element method, and the influence of the stress ratio coefficient k on the pressure and width of fractures is analyzed. The research results show that when the hydraulic fracture expands to the intersection of orthogonal joints, it will be hindered, so that the intersecting joint plane will slip and the fracture tip will be passivated, which will hinder the fracture expansion. Shear stress is the main factor that causes the obstruction. When the hydraulic fracture extends along the width direction, the shear stress changes and the hindrance decreases, so the crack can break through the hindrance and continues to extend. The extension direction is greatly affected by the value of k. When k is 0.8 and 1.0, vertical cracks extend through the horizontal joints and expand in the original direction. When k is 1.2, the vertical cracks will turn and expand along the horizontal joints. The maximum width of the hydraulic fracture and the pressure in the fracture are also greatly affected by the value of k. When k is 1.0, the maximum width of the fracture is stable, and the pressure in the fracture is unchanged. When k is 1.2, the hydraulic fracture expands along the horizontal joint after turning, the maximum width decreases, and the pressure in the fracture drops suddenly, and then gradually stabilizes. Whether the hydraulic fracture penetrates will affect the fracturing effect, a suitable stress ratio to control the direction of hydraulic fracture propagation can be chosen. Therefore, it can be a good guide for the determination of the shale hydraulic fracture propagation form and the formulation of the construction plan.

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.

The normal pressure shale gas reservoir in Southeastern Chongqing is characterized by large horizontal stress difference and high angle fracture development, so that it is difficult to form the complex fracture network and further realize the economic development. In order to solve these problems, key technologies of fracturing in normal pressure shale gas reservoir is studied. Based on the analysis of the fracturing technology of normal pressure shale gas horizontal wells in the Pengshui block, and by drawing on the successful experience of foreign marine shale gas fracturing, the scale of fracturing transformation, continuous sanding process and interim period have been continuously explored and optimized to improve the complexity of fractures and increase the volume of single section reconstruction to form a large-scale complex fracture network. Good results have been achieved in the current application in well-LY2HF and well-JY10HF of daily gas production of 9.6×10⁴ m³ and 16.7×10⁴ m³ respectively, thus realizing the economic development of normal pressure shale gas.

In order to solve the problems of long perforation cycle, high cost and self-locking of long horizontal section of coiled tubing transmission, a key test for tractor perforation has been carried out. At present, the staged fracturing of horizontal shale gas wells mainly uses pumping bridge plug perforation. In the first part of the frac well, because of the lack of pumping channels, coiled tubing transmission perforation is used usually, which need longer operating cycle and higher cost, and is not beneficial to reduce cost and improve efficiency. Nanchuan Shale Gas Field has expanded the business scope of the roller tractor by introducing and improving some tools, and realized the tractor perforation of shale gas horizontal wells. The tractor perforation powered by a tractor transports the perforation gun to the position and ignites the gun. By on-site improvement and testing, Nanchuan Shale Gas Field has solved the problems of voltage isolation protection joints, shock absorption joints and adapters, mastered the performance of tractor perforation and applicable conditions, and provided experience for subsequent construction and basis. The test results show that the perforation of the tractor in the horizontal section of shale gas wells with a well deviation of less than 90° is reliable and feasible. The tractor perforation can meet the needs of shale gas horizontal wells under pressure perforating operation. Its operation process is greatly affected by well deviation and wellbore cleanliness. Compared with coiled tubing perforation, its speed-up and cost-reducing effect is obvious. The construction period can be saved by two days, up to 50 %.

Significant advances has been made in the exploration and development of deep gas reservoirs in the southeastern Chongqing, especially the deep shale gas. While the shallow gas exploration is on the contrary, especially the shallow fracture-matrix limestone gas reservoir, Maokou Formation, with low porosity, low permeability, low fracture development, low reservoir temperature, low pressure coefficient, and mediocre fracture development. During the acid fracturing process, as the gel is hard to break by acid and the flow back is difficult, then the effect is poor, and it is difficult to make breakthrough. Taking the characteristics of carbonate reservoir, Maokou Formation in well-Dashi-1HF, as the example, the difficulties in reservoir acid fracturing have been analyzed, the self-degradation gelling acid has been synthesized, the mechanism of degradation has been introduced, and the optimization of the acid-liquid system has been carried out. The horizontal well acid fracturing pipe string has been optimized to form acid fracturing technology of self-degradation gelling acid and multilevel packer, at the same time, the segmented acid fracturing parameters have been optimized. 4 stages acid fracturing of well-Dashi-1HF has been completed, and the total acid dosage is 2 129.2 m³. The test gas production after acid fracturing is 22.6×10⁴ m³/d. The results show that this new technology has a good effect in the shallow limestone of southeastern Chongqing, and provides useful reference for the acid fracturing of similar layers in the future.

Foam drainage-gas recovery technology is the most common nowadays and is the most effective application technique. However, due to the certain difference in production conditions of different gas fields, the mode, type, and foam drainage system of foaming agents are different. At present, southern Pingqiao adopts the method of 24 h continuous injection which is commonly used in other gas fields. It works in some wells, but for other wells, this technology dose not works well. In order to form a set of foam drainage model suitable for shale gas wells in southern Pingqiao, combined with laboratory evaluation, field test and economic evaluation, it is proved that the foam drainage process can effectively carry out the bottom hole liquid accumulation and achieve a certain degree of production increase. But in the later stage, it is more focused on reducing the production decline of shale gas wells and ensuring the stable production of gas wells. The XHY-4M type liquid foaming agent is optimized for foaming. When the concentration of defoamer is 0.3 %, the concentration of defoamer is 5 % ~ 20 %, the ratio of defoamer and foaming dose is 1.2∶1, the ratio of water to gas in the well is greater than 0.5, and the overall foam drainage effect is better. Meanwhile, the foam drainage system is constantly adjusted and optimized, and the intermittent foam drainage system of “less injection and multiple times” is adopted, which is more applicable and the effect of economic evaluation is optimal. The results of this study have certain reference for the stable production of similar shale gas wells.

In order to find the injection wells with abnormal energy consumption, the energy consumption evaluation has been carried out for them. Based on the law of energy conservation, the model of single-pump corresponding to single-well is established, and the linear relationship between input power and power consumption per unit injection rate of single wells is deduced. Therefore, the straight line intercept method and the unit consumption energy saving rate method are put forward to evaluate the energy consumption of water injection systems and injection wells respectively. The results are verified by data from some water injection systems in oilfield-A in northwest and oilfield-B in northeast China. The results show that, according to theoretical analysis and field data, there is a linear relationship between the input power and the power consumption per unit of injection of a single well. The slope and intercept of straight line reflect the energy consumption of injection system and water injection well. The evaluation results of the injection system using the linear intercept method are basically consistent with the traditional system efficiency method. In addition, the evaluation of the energy consumption of injection wells by the unit consumption energy saving rate method can help to identify the injection wells with abnormal energy consumption. Combined with the actual situation on the site, the causes can be analyzed and the corresponding measures are taken to improve the efficiency of injection system.

In order to solve the problem of excess production of carbon monoxide in cyclic steam stimulation process of Hongshan oilfield, the corresponding laboratory researches have been carried out. Through physical simulation experiments and multi-parameter sensitivity analysis, the effect of technological parameters such as steam temperature, steam injection volume, and soaking time on carbon monoxide output concentration have been investigated. Furthermore, the possible solutions for carbon monoxide production have been proposed based on the effects of different factors. The results show that the influencing order of the three dominant factors is steam temperature, steam injection volume and soaking time. Reducing the steam temperature can effectively reduce the carbon monoxide output concentration, but when the steam temperature drops below 220 ℃, the crude oil production will be adversely affected. Therefore, for the wells in Hongshan oilfield with relative low carbon monoxide exceeding degree, it is recommended to reduce the steam temperature to 220 ℃ to keep the carbon monoxide concentrations below safe levels; for those ones with relative high exceeding degree, in addition to the above measures, the steam injection volume should be increased to ensure that the periodic oil production does not decrease significantly.

In the late stage of extra-high water cut, the difference of fracturing layers becomes smaller and smaller, the geological factors taken into account increase gradually, and the combination of fracturing layers becomes more and more difficult, so that, the parameters, such as reservoir, physical property, oil content and production capacity, which can reflect reservoir characteristics are optimized. By using the mutation progression method, the multiple parameters of each small layer are reduced to one comprehensive evaluation value. Through this evaluation value, the quantitative combination of fractured strata is carried out, which solves the problem that some sand bodies in the fractured strata can not be fractured due to the unreasonable combination of fractured strata in the late stage of high water cut, and realizes the efficient and intelligent combination of fractured strata. By this method, the stratified combination of 25 fractured wells in the study area is completed, and the average daily oil increase is 0.5 t more than that of a single well in the same period, achieving a better effect. It is a good reference for the quantitative combination of fractured layers.

The division of combustion stage is significance to fire drive, which can guide the production design and control in site. However, the characteristics of the previous combustion stage division methods are one-sided without considering many factors, and the applicability of its parameter index is not strong. In order to obtain a more comprehensive combustion phase division and oil displacement characteristic of in situ combustion（ISC）, the characteristics of different fire drive stages are studied by the experiment of one-dimensional combustion tube and the comparison of numerical simulation and field example of ISC. Meanwhile, the production dynamics and the characteristics of combustion front propulsion in the process of in situ combustion are compared and analyzed. 10 parameters, such as yield increase multiple, water cut, air/oil ratio, oxygen content of production well, and combustion leading edge propulsion velocity, are selected for the stage analysis to obtain the stage characteristics, which is used as the index of stage division and contrast. The conventional fire drive is divided into four stages, while the fire drive after steam huff and puff is divided into five stages. The reference standard for the division of combustion stage is established, guiding the on-site production.

The stimulation of offshore tight sandstone gas reservoirs is influenced by several factors. In order to promote the efficient development of offshore tight sandstone gas reservoirs, volumetric acid fracturing technology of offshore tight sandstone gas reservoirs is studied. And then, considering 3 problems of acid fracturing in sandstone reservoirs, 6 requirements for geology and engineering are put forward. Based on the analysis of reservoir lithological characteristics, brittleness index, stress characteristics and natural fracture development of the offshore gas field, the geological and engineering conditions of sandstone reservoir volume acid pressure are summarized. Aiming at the problems of abnormal high temperature, high breakdown pressure, water lock damage and serious water sensitivity damage, an acid liquid system is developed. The formula was 8 %HCl+5 %SA702+60 %NaBr+1 %WD-12+5 %SA601+1.5 %HJF+10 %ethanol+1 %SA1-1+1 %WD-5B+1.5 %SA1-7. Acid pretreatment can effectively reduce reservoir fracture pressure, and 9.5 MPa is reduced when applied. Volume acid fracturing is reformed by the interlayer temporary plugging steering technology using 1.5 % fibre with the length of 6 mm+0.8 % small particle+1.2 % large particle. The single well increased production ratio was 7.1, and the yield increasing effect was remarkable. This technology can provide theoretical basis and technical support for the development of tight sandstone gas reservoirs.