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.

The shale gas reservoirs in Longmaxi formation in Pengshui and its adjacent areas were overpressured in geological history, but nowadays they transformed into normal pressure. Through the simulation of formation pressure evolution in the uplifting process, it is revealed that Longmaxi shale was fractured under excessive pressure in this process, resulting in shale gas loss and therefore overpressure release. By overburden pressure permeability test, it is found that when the normal stress on the mudstone fracture surface of Longmaxi formation is more than 15 MPa, that is to say, when the buried depth is more than 1 000 m, the cracks will be closed, but the degree of fracture closure is affected by overconsolidation ratio（OCR） of shale. For the mudstone or shale under the brittle zones, OCR is relatively small, the closure degree of fracture is relatively high, the overpressure may not be completely released, and a certain degree of overpressure is still maintain. But for those above the brittle zones, the lager the OCR, the worse the fracture closure degree, and it is apt to cause the overpressure released completely, finally transit to normal pressure state. There is a significant correlation between OCR and the pressure coefficient of the formation fluid, that is, the higher the OCR ratio, the more normal the pressure will tend to be.

All the reasons that the surface limestone is exposed in a large area, the signal-to-noise ratio of seismic data is low, the underground structure is complex, and the dip angle of strata is steep make Nanchuan area to be a typical double-complex seismic geological condition of surface and underground. As the single velocity modeling method cannot obtain the accurate velocity models, it in turn affects the seismic imaging accuracy and is difficult to effectively guide horizontal well drilling in this area. In order to solve this problem, the velocity inversion of layer by layer grid tomography is carried out on the basis of structural constraints by analyzing the advantages and disadvantages of two kinds of velocity modeling methods, such as horizon chromatography and grid tomography, and combined with the actual data characteristics of Nanchuan area. That is, by picking up the seismic landmark layer with obvious longitudinal velocity variation and layer-by-layer constrained grid tomographic inversion from shallow to deep, the effect of surface and subsurface complex seismic geological conditions on velocity inversion is better reduced, and a higher precision depth domain velocity model is provided for the front depth offset . Through practical application, the imaging accuracy of seismic data in Nanchuan work area is improved obviously and basically meets the demand of shale gas exploration in this area.

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 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.

The crushability evaluation of shale reservoir is a complex system engineering. But as there are many parameters that affect the reservoir crushability, including the reservoir basic geological parameters, the rock mechanics, the formation pressure, the in-situ stress and the engineering technology, and the main influencing factors of different gas fields are different, multiple round of pilot tests are needed just to find out the main control factors affecting the productivity in complex working areas. Until now, there is no unified and authoritative evaluation method for shale reservoir crushability in China, it is extremely urgent to complete this task. Therefore, a method for shale gas reservoir crushability evaluation based on grey correlation analysis is proposed. This method has the advantages that it can quickly identify the main control sensitive parameters that affect the production. The correlation of the parameters is strong. And the production after fracturing can be predicted according to the sensitive parameters. With the increase of the number of developed wells, the prediction accuracy will be higher. In the gas field, the main control sensitive parameters can be adjusted by the optimization of engineering process, so as to further improve the fracturing effect.

How to accurately describe the distribution state of fractures formed by hydraulic fracturing in horizontal wells, the volume of reservoir transformation and the main control factors of fracture formation is one of the key technologies in shale gas development. Microseismic monitoring in the 10th to 15th fracturing section of shale gas well JY×-1 in the south of Pingqiao is carried out by means of devolving high precision geophone in adjacent well JY×-2. According to the monitoring results, the fracture development of each section of fracturing is described, and the distribution characteristics of fractures in six sections after fracturing. The main fractures are artificial fractures, whose half length is 250 m, width is 210 m, and height is 85 m. The stimulated reservoir volume（SRV） is 2 187×10 ⁴ m ³. There is a certain coincidence in the single fracturing section. The main fracture direction is 60° north of east, which is basically consistent with the direction of the maximum principal stress. Fracturing barrier is the main factor of fracture asymmetry development. Combined with the analysis of 3D seismic curvature attribute, it is considered that the natural closed fracture in the reservoir is the barrier of micro-fracture extension, which affects the extension direction and length of micro-fracture, and also leads to the increase of construction pressure.

The permeability of unconventional reservoirs is low, such as shale gas, coal-bed methane and tight gas. It is difficult to measure the permeability by the conventional method. Therefore, a method using the improved pressure depletion to measure the porosity and permeability of tight rock is proposed. The principle is to use a smaller volume gas container with a high pressure applied to one end of the rock sample and then record the process of pressure depletion. According to the variation of pressure with time, calculate the permeability and porosity of core. Therefore, the test principle is analyzed and the computational model for porosity and permeability is established, the pressure depletion rule of the typical compact shale rock samples is tested, and the effects of different factors（gas composition, temperature, confining pressure and displacement pressure） on pressure depletion and permeability are studied. The permeability values of a shale sample under different test conditions are calculated according to the experimental results. Permeability calculation results show that the permeability decreases with the increase of temperature or confining pressure, which prove that the temperature and confining pressure have important effects on permeability measurement results. Compared with the field test results, it is found that the permeability test results are consistent with it, indicating that the experimental method is reliable.

Organic-rich shale deposits in the anoxic reductive environment, and is rich in pyrite, chlorite, organic matter and other reductive components. In the process of oil and gas development, a large amount of oxidizing working fluids enter the reservoir, which is incompatible with rock and fluids in reservoir, thus breaking the physical and chemical equilibrium between shale reservoir and formation fluids such as oil, gas and water. The organic-rich shale of Silurian Longmaxi Formation in Pengshui area of southeast Sichuan Basin was selected to conduct the experiment on the interaction between oxidizing fluid and organic-rich shale, so that to analyze the effect of oxidizing working fluid on shale reservoir permeability. The results show that the after the contact of organic shale and oxidizing working fluid, the permeability will change with the fluid oxidation-reduction potential（Eh）, which is called oxygen sensitivity. When the fluid oxidation-reduction potential is less than 450 mV, the generated chemical precipitation solid particles and solid particles of shale debris, such as Fe₂O₃, Fe（OH）₃, siderite（FeCO₃）, calcium sulphate dihydrate（CaSO₄·2H₂O）, MgSO₄ and BaSO₄, lead to the reduction of shale permeability. Regulating Eh of working fluid, inhibiting oxygen sensitivity damage, and playing the role of oxidation and permeability enhancement are the development direction of completion fluid of oil and gas reservoirs under reductive environment.

The shale gas reservoirs in Pengshui Block belong to the normal pressure system, where the spontaneous production fails after hydraulic fracturing. This is due to the relative low energy and productivity of the reservoirs, hence it is necessary to deploy the artificial lift for the production wells to drainage the water throughout the whole production stage. As the drainage methods are hardly suitable for the various flowback volume in different mining stages, the water drainage efficiency is low. In order to determine the efficient drainage strategies for Pengshui Block, several drainage processes, including electric potential pump+gas lift, concentric tube（small diameter tube） drainage, self-sufficient gas lift and transmission gas lift, are comprehensively evaluated and optimized at the point of economic and technical stage according to the drainage characteristics of the block. The drainage efficiency of gas lift forms a set of drainage technology suitable for shale gas with normal pressure in Pengshui Block. The flowback efficiency of gas lift is up to 72 % in field application. It provides a significant guideline for improving the development of shale gas reservoir in Pengshui.

Accurate judgement of the wellbore flow pattern of water producing horizontal gas wells is the key to predict the wellbore production dynamics and reasonable selection of artificial lift measures. Based on the gas well production data of Pengshui block, a set of visual air-water two-phase flow simulation experimental device with variable deviation angle is designed. And the similarity criterion is used to carry out 150 groups of two-phase flow simulation experiments, including five pipe bevel angles, six gas velocities and five liquid velocities. Finally, four flow types are summarized and the influences of angle, gas velocity and liquid velocity on the convection type are analyzed. Gas velocity has a great influence on flow pattern in vertical and inclined pipe sections. With the decrease of gas velocity, flow pattern shows in turn as annular flow, agitating flow and slug flow. However, the liquid velocity has little effect on the flow pattern of each section. By comparing the experimental flow pattern with the typical flow pattern chart of the reference articals, the two-phase flow pattern chart suitable for the Pengshui block is optimized, that is, AZIZ flow pattern chart of vertical pipe + GOULD flow pattern chart of inclined pipe + GOIVER flow pattern chart of horizontal pipe. The research results can effectively predict wellbore flow pattern changes and provide technical support for the adoption of subsequent artificial lifting process.

In order to solve the problem that the injection pressure of shale reservoir in Fuling area is too high in the early stage of hydraulic fracturing, researches on the resistance reduction based on proppant slug technology was carried out. By using the previous self-developed jet device and target, a set of physical simulation method for reducing fracture resistance in near well by grinding perforation with proppant slug was established and the orthogonal experiment was carried out. For the on-site needs, fore-tail pressure drop and average pressure drop rate are established to characterize the experimental results, and then analyzed accordingly. The results show that the influence of various factors on the resistance reduction effect from large to small is in the following orders: sand ratio, particle size, number of slugs（grinding time） and proppant type. The effect of reducing resistance of quartz sand is better than that of ceramsite. Drag reduction increases with the thickening of proppant particle size and the increase of sand ratio, and decreases at first and then increases with the prolongation of grinding time. Based on the results of orthogonal experiment, the optimal operating parameters of quartz sand with particle size of 40/70 mesh, sand ratio of 9 % and grinding time of 9 min are selected. On this condition, the optimal friction reduction effect of pressure drop rate of 0.439 MPa/min and head-tail pressure drop of 1.04 MPa are obtained. The experimental study provides a certain reference for the construction design of hydraulic fracturing of shale reservoir.

During the development of high-pressure shale wells, the formation of bottom hole liquid will seriously affect the normal production. Therefore, it is necessary to keep abreast of the bottom hole liquid at any time, so as to formulate effective drainage measures in time to avoid flooding of gas wells. Traditional monitoring methods such as electronic pressure instrument hung on steel wire have many disadvantages such as complex construction technology and poor timeliness, which are often unable to meet the demands of liquid level data for gas field development. In order to solve this problem, logging unit for liquid level of shale gas wells with high pressure is introduced to monitor the liquid level, by which the liquid level height can be quickly understood. Through the liquid level testing of gas wells in the work area, the problems in the testing process are analyzed and studied. For the uncertain liquid level and other problems, the parameters such as the gain of the liquid level and coupling and so on are adjusted and the construction technology is optimized to make the instrument suitable for the well condition of the block. So that the testing technology for liquid level of South block in Pingqiao is formed. According to the well condition, the interference factors can be eliminated and the real position of liquid level can be accurately identified, and the analysis method for liquid level testing of South Block in Pingqiao is summarized. As a result, the dynamic liquid level data of single well can be obtained quickly and effectively. This method has great reference value for the formulation of single well production system and regional development scheme.

In the early stage of shale gas block in southern Pingqiao, the annular pressure phenomenon of casing production existed in high pressure shale gas wells, so that the elastic and ductile cement slurry system is optimized to improve the cementing quality and improve the long-term sealing ability of cement ring. Comprehensive analysis for the reason of this phenomenon is made, and through the physical simulation device, the sealing ability evaluation experiment of cement ring is carried out to reveal it. By interphase filling technology, the brittleness of cement is improved. Meanwhile, nano-emulsion filling technology is used to realize void filling and reduce porosity of cement and micro-ring gap. After the optimization of cement slurry system, the elastic modulus of cement slurry and the residual strain of cement slurry are reduced more than 10 % and 30 % respectively. As for as the field application of 6 wells in site, the cementing quality rate is 100 %, and the casing annulus pressure phenomenon has not happened yet. The application of low residual strain elastic ductile cement slurry system provides new technical method and means for shale gas wells to prevent annulus zone pressure, which have a good reference significance and popularization value.

Due to the own application conditions of the electric submersible pump and other drainage and gas recovery technologies, they cannot adapt to different drainage and gas recovery periods of shale gas wells in the south block of Pingqiao. In order to solve these problems, the technical adaptability analysis and countermeasures of shale gas drainage and recovery technology were carried out. Based on the analysis of the problems of electric submersible pump, jet pump and gas lift drainage and recovery process, the composite drainage and recovery process string combined by electric submersible pump and gas lift is designed according to the formation pressure characteristics of different drainage and recovery periods of shale gas wells of the south block in Pingqiao. The composite drainage and recovery process string consiste of ? 73 mm oil pipe, gas lift valve, intelligent switch and electric submersible pump. In the early production stage of shale gas wells, when the formation liquid supply capacity is sufficient, the electric pump drainage lifting process string is adopted. In the later drainage and recovery stage, when the submergence of submersible pump decreases to 100~200 m, the gas lift drainage and recovery process is adopted. This composite string overcomes the deficiency of electric submersible pump, jet pump and gas lift single drainage and recovery process, making one production string adapts to different drainage and recovery periods of shale gas wells possible, and finally realizing the continuous drainage and recovery of shale gas drainage and recovery wells.

Radial wells can be used to guide the propagation of hydraulic fractures in order to connect the natural fractures or caves in unconventional reservoirs and improve the recovery of oil and gas resources. Fracturing technology of radial wells has been preliminarily applied and developed in low permeability and shallow reservoirs, but its mechanism is still not very clear. Therefore, the basic principle of FEMM（Finite Element-Meshfree Method） is introduced. Besides, based on the FEMM and the field data, the radial well fracturing model with different well angles is established, and the effect of different azimuth angles on fracture propagation of radial well fracturing is studied. The results show that by using FEMM, it can be verified that radial wells play a guiding role in hydraulic fracturing. In addition, the hydraulic fracture firstly propagates along the direction of radial wells. After extending a certain distance, it turns to the direction of maximum horizontal stress. The bigger the angle between the radial wells and the horizontal maximum principal stress, and the shorter the length of fracture extending along the radial wells, the weaker the guiding ability of radial wells will be. The research results contribute to the application of radial well fracturing technology.

The oil reservoirs in Block-T of Yanchang Oilfield have the characteristics of low temperature and low permeability. Most of injection wells and oil wells have been fractured repeatedly, and the effect of water injection development is poor because of the water breakthrough along fracture or dominant channels. In order to solve the problems existing in the water flooding development of Block-T, combined with the advantages of air foam flooding, its field test was carried out in 2007 to explore its feasibility in low temperature and low permeability reservoirs and certain effects had been obtained. Based on the effects of the preliminary tests, its site application scale expanded after 2011. After years of field tests, the air foam flooding shows good effects in the low temperature and low permeability reservoirs now, and the complete supporting technology and safety guarantee measures have been formed. The field test shows that the measures applied in about 70 % of the single wells are effective, the average oil production per month of single well increases by 2.2 t, the comprehensive water cut reduces by 25 %, and the oil recovery improves by 1.21 %. The air foam flooding has a good effect in low temperature and low permeability reservoirs of Yanchang Oilfield.

The reservoirs of Yanhu Gas Field are shallow buried with many gas layers, whose gas bearing areas are different. The reservoirs characterized by high porosity and medium to low permeability with no unified gas-water interface are the rare small edge water gas reservoir of ultra-shallow loose sandstone layer. In general, shallow oil and gas reservoirs in China are easy to produce water and sand in the process of exploration and development, of relatively low productivity, great stable production difficulty. In the process of production the formation pressure decreases quickly, and the elastic yield is low. In order to realize the benefit development of small gas field, according to the geological characteristics of the gas field, and on the basis of reasonably division of development layer series and group, the well distribution mode along the axis, occupying high point and dense at the top and sparse at edge for Yanhu Gas Field is determined by referring to the well pattern deployment method of loose sandstone edge water gas reservoir. Then adopting the development from deep to shallow is used to succeed the production by flowback, so as to realize the targets of long-term stable production with less wells and lower cost. Therefore, succession sequence of reasonable reserves, productivity and production for gas fields is ensured. Finally, the best development effects and economic benefit are obtained.

The resistivity of water layers of part of Chang-8 oil formation of Huaqing area in Ordos Basin is higher than that of conventional ones, which leads that the water layers are often explained to be oil layers and limit the process of exploration and development of this area. In order to solve this problem, the reason is analyzed by fluid inclusions, scanning electron microscope and geology data. The results show that Chang-8 oil formation has three times of hydrocarbon flooding, the third that is the biggest extent destroyed the early formed oil-water relation. The tectonic activity from the beginning of the late Jurassic emphasizes the destroyed extent, which result in residual oil detained in the pores. Shaly interbeds further the restrain the residual oil migrating outward. The residual oil in the pore increases the resistivity of reservoir. Chlorite mineral is developed in water layers with high resistivity, whose relative content distributes in 34.32 %~81.11 %, higher than that of oil layers. The higher resistivity of water layer is caused by the adsorption of crude oil in pores by chlorite minerals on the surface of particles. In addition, carbonate minerals is also a factor of high water layer resistivity. When its content is more than 4.9 %, it will lead to high resistance of the water layer. The results reveal the formation mechanism of water layers with high resistance in Chang-8 formation in Huaqing area, which lays a foundation for the identification of high resistivity water layers in Chang-8 oil formation, the study of oil and water distribution rules and the improvement of exploration success rate in Huaqing area.

As the actual logging situation is complex, some resistivity curves of mud invasion wells only contain resistivity curve while drilling. And as the mud invasion is not complete during the measurement, conventional mud invasion correction methods can not be applied to the mud invasion correction in this kind of wells. In order to solve this problem, a new correction method is proposed, that is, the water saturation are corrected directly with the relation between water saturation before and after mud invasion according to the improved volume model. The water saturation measured by RPM is corrected directly to effectively avoid the inapplicability of resistivity logging data. Then the correction model is applied to the interpretation of logging data, and it is found that the interpretation conclusion is consistent with the actual outputs. The interpretation results of mud invasion correction by resistivity curves while drilling is corrected, which verifies the feasibility of the correction method. This method provides a new idea for the mud invasion correction.