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.

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.

Deep mountain shale gas play in Yichang, Hubei Province is located in the northern margin of Jianghan Basin in Mid-Yangtze area and has the characteristics of shale gas in Longmaxi formation such as large buried depth, complex geological condition, and large horizontal stress difference. The study of geomechanics is helpful to deepen the understanding of the influence of complex structure, fault and natural fracture system on in-situ stress field, providing basic data for wellbore stability analysis, drilling risk prediction, fracturing design optimization and post-fracturing evaluation of shale gas horizontal wells. The establishment of 3D geomechanical model depends on fine structural interpretation, shale gas geology and multi-scale natural fracture model. Therefore, one for the whole area and development platform is established. The platform scale model has more fine resolution. It can accurately depict the ground stress field around the wells and provides better service for the optimization design of drilling and fracturing. The results show that the stress mechanism in Yichang exploration area is mainly extrusion strike-slip type, the horizontal two-direction stress difference is larger than that in shale gas area of Sichuan Basin, and the risk of natural fracture activation is greater. Meanwhile, the safe window of drilling fluid is narrow and the stability of wellbore is poor. The graded fracturing of horizontal wells is affected by the large horizontal stress difference and the high risk of natural fracture activation, so the hydraulic fracture pattern is relatively simple. Based on the platform model, the 4D geomechanical simulation after fracturing is carried out, and the change of in-situ stress field after pressure is analyzed. It is showed that the minimum principal stress around the fracture net after fracturing increases significantly, the stress mechanism transitions to the reverse impulse type, and the influence range of stress shadow is 20 ~ 40 m. Making full use of geomechanical results plays an important role in improving the efficiency and development benefit of drilling engineering. This study is the first time in China to establish a fine 3D geomechanical model for the deep mountain shale gas in the complex structural area outside the Sichuan Basin. The research results have important demonstration guidance and reference significance for the large-scale development of shale gas in deep layer.

Recently, positive progress has been made in the exploration and development for shale gas of the Wufeng-Longmaxi formation in the area with complex structure of the southeast area of Chongqing. In order to further deepen the understanding of shale gas accumulation in this area, based on the previous research results, by using the data such as experimental analysis, geophysical exploration, drilling, fracturing and gas testing, and starting from the key factors of controlling shale gas enrichment and high yield, typical target anatomy and mechanism analyses are carried out to summarize the rules of shale gas enrichment and high yield. Meanwhile, it is found that the enrichment and high yield of shale gas are controlled by three factors: sedimentary facies, preservation conditions and in-situ stress field, concretely speaking, deep-water shelf facies controls the scale of resources; preservation conditions control the degree of shale gas enrichment; in-situ stress field influences the effect of fracturing transformation and controls the yield of single well. To optimize shale gas sweet spot targets and well location deployment in complex structural areas, firstly, the resource basis for controlling shale gas enrichment should be evaluated, that is, the development degree and indicators of high-quality shale in deep-water shelf facies. Secondly, the intensity of tectonic movements is evaluated to determine the preservation conditions and enrichment degree of shale gas. Finally, it is preferred to deploy a shale gas well with a medium-curvature zone of moderate in-situ stress to facilitate high and stable yield. The research results have important guidance and reference significance for the exploration and development of shale gas in complex structural areas.

By the observation of the organic microscopic composition and scanning electron microscopy of the whole rock, the black shale of the Upper Ordovician Wufeng-Lower Silurian Longmaxi formation in Pengshui and its adjacent core wells Microscopic observation, classification and research of hydrocarbon-forming organism systems. It is found that the main hydrocarbon-forming organism types of shale in Pengshui and its adjacent areas are alginite（phytoplankton, suspected sources, benthic algae, etc.）, animal debris（graptolite, radiolarian, chitinozoa and foraminifera） and bacteria, etc. Among them, the main hydrocarbon-forming organisms in organic-rich shale in Wufeng-Longmaxi formation（TOC≥2.0 %） are phytoplankton, suspected sources, bacteria, graptolite, etc., which have high abundance and differentiation. Hydrocarbon-forming organisms are the main source of oil and gas, meanwhile, the organic pores formed after its complex thermal evolution are the main carriers of shale gas occurrence. As there is a good coupling relationship between source and reservoir in the organic-rich shale section of Wufeng-Longmaxi formation, it is supposed to be the best geological sweet spot layer.

Micro-pore connectivity affects the seepage and production of shale gas, but there are less research on shale connectivity currently. Taking the Wufeng-Longmaxi formation shale gas reservoir in Pengshui area as an example, the connected pore assemblages of shale gas reservoirs were classified, and then the pore-throat connections of different types of shales were discussed based on a variety of experimental methods. Four types of connected pore assemblages were classified in shale, that is, organic pore interconnection, organic pore-micro-fracture interconnection, organic pore-clay pore interconnection, and clay pore-intergranular pore interconnection. Organic-rich shale, mainly composed of interconnected organic pore assemblages, conforms to the short-conduit pore-throat assemblage model with the minimum pore-throat ratio. While medium-low organic shale, mainly composed of interconnected organic pore-clay pore assemblages, is a composite model of short-conduit and tree-shaped pore with the relatively large pore-throat ratio. When the ratio of TOC/clay mineral content decreases, the tree-shaped pore-throat ratio increases and the pore-throat ratio decreases. The combination of small pore throat ratio and high content organic pore interconnection is conducive to reducing water lock damage caused by fracturing fluid retention.

The production of shale gas is a complex and multiscale process that spans a variety of scales and goes through a variety of mass transfer mode. The stress sensitivity of each path has an important influence on the mass transfer of shale gas. Especially when a large amount of fracturing fluid retained in shale reservoir, water-rock interactions will inevitably affect shale stress sensitivity. Taking Longmaxi Formation shale in the southeast area of Chongqing as the research object, stress sensitivity experiments of shale before and after water-rock interactions are carried out, which characterize the change characteristics of fracture surface properties before and after stress sensitivity experiments, and analyze the action mechanisms of water-rock interaction on the fracture surface. It is found that, the stress sensitivity of fractured shale containing proppants is weak, and the existence of proppants reduce the stress sensitivity of shale. The wider the crack width is, the stronger the stress sensitivity will be. The stress sensitivity of shale after water-rock interaction is from high to low in the following order: alkali sensitivity>salt sensitivity with reduced salinity>water sensitivity. In the process of salt sensitivity and water sensitivity with reduced salinity, clay minerals hydrate and expand, and particles migrate, resulting in smoother fracture surfaces. However, the alkali-sensitive process, the fluid not only hydrates with the fracture surface, but also causes the alkali erosion, which strengthens the shale stress sensitivity. The stress sensitivity of fracture shale containing proppant is weakened, and the embedding and crushing of propelling agent is the main cause of stress sensitivity. The optimal selection and reasonable laying of propelling agent is the key to reduce the stress sensitivity.

The productivity of gas wells in conventional gas reservoirs is mainly measured by open flow rate. The open flow rate is determined by gas test and production test data to evaluate the productivity of gas wells. Because of the particularity of geological characteristics and seepage mechanism, it is controversial to use which indexes to characterize the productivity of shale gas wells. Combined with the testing and production data of actual shale gas wells in China, it is proposed that the productivity of shale gas wells in different development stages can be characterized by three kinds of indexes—unhindered flow rate, recoverable reserves and gas production. When the productivity of shale gas wells is characterized by open flow, the empirical formula of “one point method” in Fuling main area is established, and the reservoir capacity（α） is 0.25. For the production capacity test of multiple work systems, the multi-flow method has better adaptability in Fuling. When the productivity of shale gas wells is characterized by recoverable reserves, before shale gas wells enter the decline stage, the unsteady productivity evaluation method of shale gas fractured horizontal wells is selected; while after entering the decline stage, the recoverable reserves of shale gas wells can be predicted by empirical decline method. For shale gas wells with fixed production, the gas test production of the same oil nozzle can be optimized to characterize the productivity of shale gas wells. The research results lay a foundation for the dynamic analysis of shale gas well production and the formulation of development technology policy.

Shale gas development is in an important position of natural gas development strategy for Sinopec, and numerical simulation technology is an important technical means to optimize the policy and scheme of development technology, predict the production performance of gas wells, study the production rule, and track and optimize the development of gas fields. The traditional numerical simulation method of shale gas development adopts equivalent medium model, can not depict the distribution of crack network after fracturing, and is unable to accurately predict the production of layered reserves, so that it can not meet the needs of the field. Therefore, a new method for shale gas simulation based on embedded fracture modeling is proposed. This method consists with four stages:①to establish geological structure model; ②to describe the fracture characteristics of the fracture network based on micro-seismic data, and then embed it in the geological model background grid and calculate the conductivity; ③to fit the production data and adjust the fracture parameters; ④to prediction and analyze the productivity and production of reservoir reserves for multi-stage fracturing horizontal wells. The proposed method has been applied to a three staged fracturing wells in Fuling shale gas reservoir and the utilization of the reserve in the well is analyzed. It provides technical support for the next adjustment scheme of the platform.

With the increasing demand for energy, shale gas, as a new type of unconventional natural gas resource, has attracted more and more attention. At present, the commercial development of high pressure shale gas reservoir in China has been successfully realized, but the efficient development technology of shale in deep layer and normal pressure shale is still in the exploratory stage. The normal pressure shale reservoirs in China are mainly located in the residual syncline outside the basin. The deformation degree of structure is strong, the formation pressure coefficient is between 0.9 and 1.3, the buried depth is generally shallow, the formation energy is insufficient, and the daily production of single well after fracturing is （1~5）×10 ⁴m ³. All those problems result in the failure of commercial breakthrough so far. The fracturing technologies of high-pressure shale gas reservoirs have little effect in the process of normal-pressure shale reconstruction. Based on the difficult problems in the transformation of atmospheric shale gas wells, optimization has been carried out on many aspects such as the perforation mode, artificial fracture control and support technology, field construction technology and fracturing materials. The suitable network fracturing with high density is researched, and the multi-cluster fracture equilibrium extension and multi-scale artificial fracture network are preliminarily realized. The scheme has been tested in an normal pressure shale gas well of a certain shale gas block in southeast Chongqing, and good reconstruction effect has been obtained after fracturing.

Rock anti-drillability parameters are important basic parameters for making drilling plan and implementing optimal drilling. In this paper, the computational models of formation anti-drillability parameters such as rock compressive strength, rock drillability level value and rock hardness are established through the rock mechanics testing. After that, combined with the logging data and geological data, the profiles of rock anti-drillability parameters varied with the well depth of different strata for shale gas in Nanchuan are also built up. Based on the analysis of its distribution rule, the bits are selected. The study shows that the characteristic parameters of the strata above Liangshan Formation in the shale gas block of Nanchuan fluctuate greatly, which indicates that the stratigraphic heterogeneity is obvious; the lower strata change more gently, but there is a gradual upward trend from the bottom of Longmaxi Formation. According to rock anti-drillability parameters, bits with good wear resistance, 5 ~ 6 blades, and 13 ~ 16 mm cutting teeth with high density should be selected in bit design. The field application shows that the recommended bit has a good effect and the drilling speed is obviously improved.