Shale Gas In China Research Articles

China's Shale Gas Geological Investigation and Prospecting Have Made Significant Progress

China's Shale Gas Geological Investigation and Prospecting Have Made Significant Progress

Can Switching from Coal to Shale Gas Bring Net Carbon Reductions to China?

To increase energy security and reduce emissions of air pollutants and CO2 from coal use, China is attempting to duplicate the rapid development of shale gas that has taken place in the United States. This work builds a framework to estimate the lifecycle greenhouse gas (GHG) emissions from China's shale gas system and compares them with GHG emissions from coal used in the power, residential, and industrial sectors. We find the mean lifecycle carbon footprint of shale gas is about 30-50% lower than that of coal in all sectors under both 20 year and 100 year global warming potentials (GWP20 and GWP100). However, primarily due to large uncertainties in methane leakage, the upper bound estimate of the lifecycle carbon footprint of shale gas in China could be approximately 15-60% higher than that of coal across sectors under GWP20. To ensure net GHG emission reductions when switching from coal to shale gas, we estimate the breakeven methane leakage rates to be approximately 6.0%, 7.7%, and 4.2% in the power, residential, and industrial sectors, respectively, under GWP20. We find shale gas in China has a good chance of delivering air quality and climate cobenefits, particularly when used in the residential sector, with proper methane leakage control.

Suggestions on the development strategy of shale gas in China

From the aspects of shale gas resource condition, main exploration and development progress, important breakthrough in key technologies and equipment, this paper systematically summarized and analyzed current situation of shale gas development in China and pointed out five big challenges such as misunderstandings, lower implementation degree and higher economic uncertainty of shale gas resource, and still no breakthrough in exploration and development core technologies and equipment for shale gas buried depth more than 3500 m, higher cost and other non-technical factors that restrict the development pace. Aiming at the above challenges, we put forward five suggestions to promote the shale gas development in China: (1) Make strategies and set goals according to our national conditions and exploration and development stages. That is, make sure to realize shale gas annual production of 20 × 109 m3, and strives to reach 30 × 109 m3. (2) Attach importance to the research of accumulation and enrichment geological theory and exploration & development key engineering technologies for lower production and lower pressure marine shale gas reservoir, and at the same time orderly promote the construction of non-marine shale gas exploration & development demonstration areas. (3) The government should introduce further policies and set special innovation funds to support the companies to carry out research and development of related technologies and equipment, especially to strengthen the research and development of technology, equipment and process for shale gas bellow 3500 m in order to achieve breakthrough in deep shale gas. (4) Continue to promote the geological theory, innovation in technology and management, and strengthen cost control on drilling, fracturing and the whole process in order to realize efficient, economic and scale development of China's shale gas. (5) Reform the mining rights management system, establish information platform of shale gas exploration and development data, and correctly guide the non-oil and gas companies to participate in shale gas exploration and development.

Progress in key technologies for evaluating marine shale gas development in China

Abstract The Lower Paleozoic Longmaxi and Qiongzhusi Formatiion shale plays were taken as research objects to summarize the geologic and reservoir characteristics of marine shale gas in China. Based on the theory and technology achievements made during the twelfth five-year plan, a key index system was established to evaluate shale gas well production effect in China, and a comprehensive classification was consequently presented by integrating geological statistical indexes and economic evaluation indexes; to characterize the complex fracture network formed by fracturing, a generalized analytical model was established by incorporating fractal and continuum geometry theory to capture the transient behavior of such fractured horizontal well throughout production life. An associated probabilistic analysis, based on the Monte Carlo simulation was presented by linking a probabilistic worksheet with the analytical model, and then used to determine a range of possible outcomes (i.e., EUR, decline rate and production time). Meanwhile, an optimization approach for development parameters, including fractured horizontal segment, fracture geometry (i.e., fracture length, conductivity, number), well spacing and drawdown management was advanced. There are still many unresolved problems on geologic theory, flow mechanism and productivity evaluation method, development technical policy and economic benefits, which limit large-scale and high-efficiency exploitation of shale gas resource in China.

Prediction of marine shale gas production in South China based on drilling workload analysis

The marine shale gas resource in South China is abundant, but the existing conventional methods cannot meet the needs of predicting the future production development of shale gas. With the marine shale of the Lower Silurian Longmaxi Fm in this region as an example and based on its development potential, the development features of the existing shale gas resources were analyzed. It is considered that the Longmaxi shale gas accumulation zones in the Sichuan Basin and its neighboring areas contain resources of about 17.4 × 1012 m3 and recoverable resources of about 2.9 × 1012 m3. In particular, the shale gas above 3500 m underground is the main body for recent development targets, with a potential production scale about 300 × 108 m3. On this basis, the development features of foreign and domestic shale gas wells were studied and the drilling workload analytical method for the prediction of shale gas production was established: (1) the initial production of a single well can be used to characterize the productivity of the shale gas well, and its test production is approximate to its initial production. Due to the similarity of decline rate among shale gas wells, the single-well estimated ultimate recovery (EUR) value of a single well can be roughly speculated from its initial production, thus the production scale of a shale gas field can be speculated according to the analysis of drilling workload; (2) currently, the expected test production of South China marine shale gas is 17.6 × 104 m3/d, and the predicted single-well EUR value is roughly 1.5 × 108 m3. It is concluded that the marine shale gas in South China represents high initial production of a single well, high declining rate, longer production cycle and the drilling workload is closely related with the production of a shale gas field. Therefore, the analysis of drilling workload shows better applicability to the evaluation of shale gas production. Based on this method, the shale gas production of the Sichuan Basin and its neighboring area in 2020 was estimated to be about 200 × 108 m3.

China Shale Gas Reservoir Types and Its Controlling Factors

China Shale Gas Reservoir Types and Its Controlling Factors

Pore characterization and methane sorption capacity of over-mature organic-rich Wufeng and Longmaxi shales in the southeast Sichuan Basin, China

Currently, the Upper Ordovician Wufeng (O3w) and Lower Silurian Longmaxi (S1l) Formations in southeast Sichuan Basin have been regarded as one of the most important target plays of shale gas in China. In this work, using a combination of low-pressure gas adsorption (N2 and CO2), mercury injection porosimetry (MIP) and high-pressure CH4 adsorption, we investigate the pore characteristics and methane sorption capacity of the over-mature shales, and discuss the main controlling factors for methane sorption capacity and distribution of methane gas in pore spaces.Low pressure CO2 gas adsorption shows that micropore volumes are characterized by three volumetric maxima (at about 0.35, 0.5 and 0.85 nm). The reversed S-shaped N2 adsorption isotherms are type Ⅱ with hysteresis being noticeable in all the samples. The shapes of hysteresis loop are similar to the H3 type, indicating the pores are slit- or plate-like. Mesopore size distributions are unimodal and pores with diameters of 2–16 nm account for the majority of mesopore volume, which is generally consistent with MIP results. The methane sorption capacities of O3w-S1l shales are in a range of 1.63–3.66 m3/t at 30 °C and 10 MPa. Methane sorption capacity increase with the TOC content, surface area and micropore volume, suggesting organic matter might provide abundant adsorption site and enhance the strong methane sorption capacity. Samples with higher quartz content and lower clay content have larger sorption capacity. Our data confirmed that the effects of temperature and pressure on methane sorption capacity of shale formation are opposite to some extent, suggesting that, during the burial or uplift stage, the gas sorption capacity of hydrocarbon reservoirs can be expressed as a function of burial depth. Based on the adsorption energy theory, when the pore diameter is larger than 2 nm, much methane molecular will be adsorbed in pores space with distance to pore wall less than 2 nm; while free gas is mainly stored in the pore space with distance to pore wall larger than 2 nm. Distributions of adsorption space decrease with the increasing pore size, while free gas volume increase gradually, assuming the pore are cylindrical or sphere. Particularly, when the pore size is larger than 30 nm, the content of adsorbed gas space volume is very low and its contribution to the all gas content is negligible.

Key geological issues and main controls on accumulation and enrichment of Chinese shale gas

Abstract By analyzing geological characteristics of shale gas in Southern China and the United States, main factors controlling the accumulation and key issues in the exploration and development of shale gas in China have been examined. The geological characteristics of shale gas in China include multi-stage tectonic evolution, complex structure types, abundant faults, small continuous distribution area of shale formations, and no corresponding relationship between current thermal evolution degree and current burial depth of two main sets of shale formations (the Cambrian and Silurian). According to the analysis of the factors affecting shale gas enrichment such as fracture, tectonic type, shale gas migration, and gas content etc, the enrichment mechanisms of shale gas in China are: “sedimentary facies and preservation condition” are the main reservoir-controlling factors affecting the accumulation of shale gas, and “structure types and tectonism” are the main factors controlling the enrichment of shale gas in China; The former factors define shale gas plays, and the latter ones determine the position of sweet spots. The future research directions of shale gas in China are: firstly, contrary to the shale gas development in the United States, shale gas exploration and development in China should extend from the overpressure to normal pressure, and even low pressure areas; secondly, shale gas exploration in the Sichuan basin should extend from middle-deep to deep formations, studies should be done on the shale gas enrichment mechanism and accumulation models in formations deeper than 4 000 m, and horizontal well fracturing technology for these formations; thirdly, the development of transitional facies and continental facies shale gas should be brought along by drawing on exploration and development experience of marine shale gas.

Logging identification for the Lower Cambrian Niutitang shale reservoir in the Upper Yangtze region, China: A case study of the Cengong block, Guizhou Province

Currently, China has achieved a breakthrough in the Lower Silurian Longmaxi shale in Sichuan Basin and its surrounding areas. Compared to the Longmaxi shale, the Lower Cambrian Niutitang shale, which has a greater deposition thickness and wider distribution area, is another significant stratum for China's shale gas. Geophysical well logging is one of the most significant methods used for identification and evaluation of shale gas reservoirs throughout the process of shale gas exploration and development. In this paper, the logging response of the Niutitang shale is summarized to “four high and four low”, this was determined through a comparative analysis of three shale gas wells in the Cen'gong block. The Geochemical logging (GEM) data shows that as the depth goes deeper the content of Si (quartz) increases and the content of Al, Fe, K (Potassium), and Clay minerals decreases. In addition, the Niutitang shale mainly has the feature of a single peak or two continuous peaks in T2 spectrum on the nuclear magnetic resonance (NMR) logging response. This has a longer T2 time and greater amplitude than normal shales. The logging response of various lithology and preservation is summarized by overlapping and a cross-plot analysis with the spectral gamma-ray, resistivity, density, acoustic, and compensated neutron logging data, which are sensitive to organic-rich shales. Moreover, the resistivity and acoustic logging data are sensitive to gas content, fluid properties, and preservation conditions, which can be used as indicators of shale gas content and preservation.

Geochemical characteristics of marine and terrestrial shale gas in China

Although the annual production of shale gas in China was 13 × 108 m3 in 2014, a systematic study on geochemical and isotopic characteristics of these unconventional gases has not been well addressed. In the present study, almost all shale gas samples available in China, including marine shale gas from the Wufeng-Longmaxi Formation in the Sichuan Basin (O3w–S1l) and terrestrial shale gas from Chang 7 Member (T3y7) in the Ordos Basin, were collected and analyzed for their geochemical and isotopic compositions. The shale gas from the Wufeng-Longmaxi Shale is dry gas with an average methane content of 98.38% and records a highest content of CH4 in the world (99.59%), which is consistent with the very high thermal maturity levels of the gas shales that have equivalent vitrinite reflectance (EqVRo) values between 2.4 and 3.6%. The δ13C1 values are correspondingly heavy and record a heaviest δ13C1 values (−26.7‰) for the shale gases found in the world as well. The average values of δ13C1, δ13C2 and δ13C3 for the Wufeng-Longmaxi shale gas are −31.3‰, −35.6‰, and −47.2‰, respectively, displaying a complete carbon isotopic reversal (i.e., δ13C1 > δ13C2 > δ13C3). δ2HCH4 and δ2HC2H6 has an average value of −148‰ and −173‰, respectively, also yielding a hydrogen isotopic reversal (i.e., δ2HCH4 > δ2HC2H6). The Chang 7 shale has an average TOC content of 13.81% with vitrinite reflectance (VRo) values between 0.7 and 1.2%. The Chang 7 shale gas is wet gas with an average methane content of 84.90% and is rich in heavy gaseous hydrocarbons (C2–C5). The respective values of δ13C1, δ13C2 and δ13C3 are −48.7‰, −36.4‰ and −31.3‰, displaying a positive carbon isotopic distribution pattern (i.e., δ13C1 < δ13C2 < δ13C3). The average δ2HCH4, δ2HC2H6 and δ2HC3H8 values are −256‰, −244‰ and −188‰, respectively, and are characterized by a positive distribution pattern (i.e., δ2HCH4 < δ2HC2H6 < δ2HC3H8). The differences in gas wetness and carbon and hydrogen isotopic distribution patterns between the shale gases from the Wufeng-Longmaxi and Chang 7 shale are attributed to variations in thermal maturity levels. CO2 is present in low content in both the Wufeng-Longmaxi and Chang 7 shale gases, mostly less than 1%. δ13C values for the CO2 in the Wufeng-Longmaxi Formation are between 8.9 and −9.2‰, indicating an inorganic origin from the cracking of carbonate mineral in the shales under high temperatures. In contrast, δ13C values of the CO2 in the Chang 7 shale gas range from −8.2 to −22.7‰, indicating an organic origin from the thermal degradation of organic matter. Helium in both the Wufeng-Longmaxi and Chang 7 shale gases is dominantly of curst origin in terms of their R/Ra ratios that vary from 0.01 to 0.08. Positive carbon isotopic distribution pattern is typical of primitive thermogenic gas. However, it can be converted into complete or partial carbon isotopic reversal patterns due to secondary alteration. The causes that yield carbon isotopic reversal include (1) mixing of gases with the same source but different thermal maturity levels; (2) secondary cracking of oil or wet gas; (3) formation water-involved reactions; (4) gas diffusion; and (5) carbon isotope exchange between alkane gases at high temperature. Among them, carbon isotopic exchange between alkane gases at high temperature is a key factor. Nine plots have been drawn based on the shale gases from China, USA and Canada. Among them, the plot of δ13C2 versus wetness demonstrates a “lying-S” shape with two inflection points on the gas wetness axis. The wetness value of 1.4% represents a critical point from pyrolytic gas (primary cracking gas) to cracking gas (secondary cracking gas) and whereas the wetness value of 6% marks the end of oil generation. On the diagram of wetness versus δ13C, shale gases with wetness values greater than 1.6% are characterized by positive carbon isotopic distribution pattern, whereas a complete or partial carbon isotopic reversals are observed for shale gases with wetness values less than 1.6%.

Shale gas in China: Characteristics, challenges and prospects (II)

Shale gas in China: Characteristics, challenges and prospects (II)

Unstable seepage modeling and pressure propagation of shale gas reservoirs

Pressure disturbance propagation was investigated using the steady state replacement method, the relationship between moving boundary and time was obtained. An unstable seepage model in shale gas reservoirs was established considering the effects of desorption, diffusion, slip and moving boundary. Using Laplace transform, the pressure characteristics equation was solved for the condition of internal boundary being constant production and outer boundary being the moving boundary. Subsequently, combining the parameters of shale gas in southern China, unstable seepage pressure characteristics and its influence factors of shale gas reservoir were analyzed using MATLAB software. The results indicate that the pressure propagation is characterized by moving boundary effect during shale gas exploitation, which means that moving boundary is propagated outwards with the propagation velocity decreasing gradually. Under the effect of moving boundary or shale gas desorption, the pressure propagation velocity decreases and the reservoir pressure drop slows down. With the increasing of the diffusion coefficient, the reservoir pressure drop slows down and the effect of diffusion coefficient decreases gradually. In the process of gas reservoir exploitation, diffusion and slip contribute more and more to gas production, acting as the dominant factors, while the contribution of flow and desorption level off after decreasing.

Application of high-precision 3D seismic technology to shale gas exploration: A case study of the large Jiaoshiba shale gas field in the Sichuan Basin

The accumulation pattern of the marine shale gas in South China is different from that in North America. The former has generally thin reservoirs and complex preservation conditions, so it is difficult to make a fine description of the structural features of shale formations and to reflect accurately the distribution pattern of high-quality shale by using the conventional 2D and 3D seismic exploration technology, which has an adverse effect on the successful deployment of horizontal wells. In view of this, high-precision 3D seismic prospecting focusing on lithological survey was implemented to make an accurate description of the distribution of shale gas sweet spots so that commercial shale gas production can be obtained. Therefore, due to the complex seismic geological condition of Jiaoshiba area in Fuling, SE Sichuan Basin, the observation system of high-precision 3D seismic acquisition should have such features as wide-azimuth angles, small trace intervals, high folds, uniform vertical and horizontal coverage and long spread to meet the needs of the shale gas exploration in terms of structural interpretation, lithological interpretation and fracture prediction. Based on this idea, the first implemented high-precision 3D seismic exploration project in Jiaoshiba area played an important role in the discovery of the large Jiaoshiba shale gas field. Considering that the high-quality marine shale in the Sichuan Basin shows the characteristics of multi-layer development from the Silurian system to the Cambrian system, the strategy of shale gas stereoscopic exploration should be implemented to fully obtain the oil and gas information of the shallow, medium and deep strata from the high-precision 3D seismic data, and ultimately to expand the prospecting achievements in an all-round way to balance the high upstream exploration cost, and to continue to push the efficient shale gas exploration and development process in China.

Technologies in Discovery and Exploration of Fuling Shale Gas Field, China

Marine shale gas in South China is widely distributed and demonstrates an enriched resource. Compared with the North American commercial shale gas field, the shale formation in South China is featured by old age, multiple stages tectonic movements, and high thermal evolution degree and complex reservoir forming conditions. As a result, the existing theories and technical methods of exploration in North America cannot be simply applied to South China. Since 2007, based on the in-depth study on a large quantity of analytical test data, we have conducted the theory and technology research for the southern marine shale gas, found Wufeng-Longmaxi Group deep water shelf high-quality shale gas critical parameters coupling laws, proposed the “Binary Enrichment” theory for highly evolved marine shale gas in southern complex tectonic zone, and established a zone selection and evaluation criteria, which are based on the quality of shale, for the key of preservation condition, and for the purpose of economy. Taking this as a guide, we selected Longmaxi formation Lower Silurian of Fuling area in southeastern Sichuan Province as the preferred breakthrough field for the shale gas exploration. The Jiaoye 1 well has the daily gas production of 20.3 × 104 m3, which embarked the found of China’s first large-scale business development gas field, the Fuling shale gas field. And we submit the first domestic shale gas proven reserves of 1067.5 × 108 m3. The Fuling shale gas reservoirs are deep water shelf marine high-quality shale, with favorable thickness and even distribution, without dissection in the middle. They are typical self-generation and self-storage shale gas reservoirs. The gas fields have high production gas well; high pressure gas reservoir, good gas components and good exploit results, and there for the Fuling shale gas field is characterized by mid-depth, high pressure, high reservoir pressure, and high quality gas accumulation. Up to March 24, 2014, all of the 101 fracture-gas testing wells have obtained middle and upper shale airflow, with the average single well test production of 32.6 × 104 m3/d. In the exploration and development process, technology series in geological evaluation, horizontal well, drilling, well completion, piecewise fracturing techniques have been gradually formed. It is of great importance to commercially develop the domestic shale gas and promote the restructuring of China’s energy structure.

Comprehensive evaluation technology for shale gas sweet spots in the complex marine mountains, South China: A case study from Zhaotong national shale gas demonstration zone

The exploration and development of marine shale gas reservoirs in South China is challenged by complex geological and geographical conditions, such as strong transformation, post maturity, complex mountains and humanity. In this paper, the evaluations on shale gas sweet spots conducted in Zhaotong demonstration zone in the past six years and the construction of 500 million m3 shale gas productivity in Huangjinba region were discussed, and the results of shale gas reservoir evaluations in China and abroad were investigated. Accordingly, it is proposed that another two key indicators be taken into consideration in the evaluation on shale gas sweet spots in marine mountains in South China, i.e. shale gas preservation conditions and pore pressure, and the research on ground stress and natural microfracture systems should be strengthened. Then, systematic analysis was conducted by integrating shale gas multidisciplinary data and geological and engineering integration study was carried out. Finally, a 3D model, which was composed of “geophysics, reservoir geology, fracture system and rock geomechanics”, was established for shale gas reservoirs. Application practice shows that the geological engineering integration and the 3D reservoir modeling are effective methods for evaluating the shale gas sweet spots in complex marine mountains in South China. Besides, based on shale gas sweet spot evaluation, 3D spatial congruency and superposition effects of multiple attributes and multiple evaluation parameters are presented. Moreover, the short-plate principle is the factor controlling the distribution patterns and evaluation results of shale gas sweet spots. It is concluded that this comprehensive evaluation method is innovative and effective in avoiding complex geological and engineering risks, so it is of guiding significance in exploration and development of marine shale gas in South China.

Comparative Study and Analysis of the Development of Shale Gas between China and the USA

In the 21st century, the shale gas is a greatly potential unconventional gas resource, which can serve as an important complement to conventional energy sources, and can effectively alleviate the energy pressure of the world. The development of shale gas in the USA is in the developing stage with advanced exploitation technology and huge reserves. Compared with the USA, the development of shale gas in China is still in the early stage. The development of shale gas is both an opportunity and a challenge. Chinais in the exploration and preparation stage of resource assessment and exploration. This paper presents the importance of the formation principle of shale gas and the energy application, and compares the progress of shale gas studies, exploitation technology as well as the study hot-points betweenChinaand theUSA. Meanwhile, this paper states the difficulties and challenges with the development of shale gas inChina.

2D Multitransient Electromagnetic Response Modeling of South China Shale Gas Earth Model Using an Approximation of Finite Difference Time Domain with Uniaxial Perfectly Matched Layer

In this study, we introduced multitransient electromagnetic (MTEM) method as an effective tool for shale gas exploration. We combined the uniaxial perfectly matched layer (UPML) equation with the first derivative diffusion equation to solve for a finite difference time domain (FDTD) UPML equation, which was discretized to form an algorithm for 3D modeling of earth impulse response and used in modeling MTEM response over 2D South China shale gas model. We started with stepwise demonstration of the UPML and the FDTD algorithm as an effective tool. Subsequently, quantitative study on the convergence of MTEM earth impulse response was performed using different grid setup over a uniform earth material. This illustrates that accurate results can be obtained for specified range of offset. Furthermore, synthetic responses were generated for a set of geological scenarios. Lastly, the FDTD algorithm was used to model the MTEM response over a 2D shale gas earth model from South China using a PRBS source. The obtained apparent resistivity section from the MTEM response showed a similar geological setup with the modeled 2D South China shale gas section. This study confirmed the competence of MTEM method as an effective tool for unconventional shale gas prospecting and exploitation.

Analysis of developmental characteristics and dominant factors of fractures in Lower Cambrian marine shale reservoirs: A case study of Niutitang formation in Cen’gong block, southern China

Abstract Fractures are important to shale gas reservoirs because they can increase the storage spaces and seepage pathways. In addition, natural fracture systems are important to hydraulic-fracture stimulation to form fracture networks. Currently, China has achieved a breakthrough of the Lower Silurian Longmaxi formation in Sichuan basin and its surrounding areas. Compared with the Longmaxi shale, the Lower Cambrian Niutitang shale has greater TOC content, depositional thickness and wider distribution areas; thus, it is another significant stratum for China's shale gas. This paper discusses the characteristics and dominant factors of fractures and their relationship to the gas content in the Niutitang shale based on several types of data: observations and descriptions of fracture systems in outcrops, drilling cores, casting thin sections and field-emission scanning electron microscopy (FE-SEM); detailed fracture characteristics and parameters; and analyzes and tests of corresponding fracture segment samples. The results indicate that the Niutitang shale has similar brittle mineral and TOC content as Barnett shale, except that it has a higher maturity (equivalent Ro>2.2%). Multiple types of fractures are abundant and have suffered multi-stage activation and modification; these are mainly structural fractures due to the late diagenetic stage and multi-stage tectonic movements in southern China. The primary types of micro-fractures are interlayer, inter-particle and intra-particle fractures. The fractures with scratches have abundant pores in mylonitic minerals, and unsealed fractures (inter-particle, intra-particle fractures, and cleavages) and pores (inter-particle, intra-particle and dissolved) in the cement of the fractures and have improved the effectiveness of sealed fractures. The development of fractures is controlled by structural factors, mineral composition, TOC, reservoir heterogeneity, lithology and rock mechanical properties, and the structural factor is the uppermost. Within the same tectonic setting, the content of the brittle minerals, brittleness (rock mechanical properties), and heterogeneity are positively correlated with the fracture density. When the TOC is less than 6.5 wt%, the fracture density, porosity and brittleness display positive correlations with TOC; however, when the TOC is greater than 6.5 wt%, the positive correlations become negative. The high quartz content (rigid particles), which is usually accompanied with high TOC, favors the development and preservation of micro-pores and fractures. Fractures have played important roles in seepage pathways, storage spaces, and interconnections of isolated micro-pores, which leads to positive correlations between the fracture density, total and desorbed gas content. Knowledge regarding this area will guide the exploration and development of shale gas and is helpful in optimizing the intervals of drilling and fracturing stimulation.

Shale gas in China: Characteristics, challenges and prospects (I)

Abstract This paper mainly discusses the industrialization progress, “sweet spot” evaluation criterion, E&P technologies, success experiences, challenges and prospects of China's shale gas. Based on the geologic and engineering parameters of the Fuling, Changning and Weiyuan shale gas fields in the Sichuan Basin, this paper points out that China's shale gas has its particularity. The discoveries of super-giant marine shale gas fields with high evolution degree (R o =2.0%−3.5%) and ultrahigh pressure (pressure coefficient=1.3−2.1) in southern China is of important scientific significance and practical value to ancient marine shale gas exploration and development to China and even the world. It's proposed that shale gas “sweet spots” must be characterized by high gas content, excellent frackability and good economy etc. The key indicators to determine the shale gas enrichment interval and trajectory of horizontal wells include “four highs”, that is high TOC (>3.0%), high porosity (>3.0%), high gas content (>3.0 m 3 /t) and high formation pressure (pressure coefficient>1.3), and “two well-developed” (well-developed beddings and well-developed micro-fractures). It's suggested that horizontal well laneway be designed in the middle of high pressure compartment between the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation. The mode of forming “artificial shale gas reservoir” by “fracturing micro-reservoir group” is proposed and the mechanisms of “closing-in after fracturing, limiting production through pressure control” are revealed. Several key technologies (such as three-dimensional seismic survey and micro-seismic monitoring of fracturing, horizontal wells, “factory-like” or industrialized production mode, etc.) were formed. Some successful experiences (such as “sweet spot” selection, horizontal well laneway control, horizontal length optimization and “factory-like” production mode, etc.) were obtained. The four main challenges to realize large-scale production of shale gas in China include uncertainty of shale gas resources, breakthroughs in key technologies and equipment of shale gas exploration and development below 3 500 m, lower cost of production, as well as water resources and environment protection. It is predicted that the recoverable resources of the Lower Paleozoic marine shale gas in southern China are approximately 8.8×10 12 m 3 , among which the recoverable resources in the Sichuan Basin are 4.5×10 12 m 3 in the favorable area of 4.0×10 4 km 2 . The productivity of (200−300)×10 8 m 3 /a is predicted to be realized by 2020 when the integrated revolution of “theory, technology, production and cost” is realized in Chinese shale gas exploration and development. It is expected in the future to be built “Southwest Daqing Oilfield (Gas Daqing)” in Sichuan Basin with conventional and unconventional natural gas production.

Review on Research and Development of Shale Gas in China

Shale gas reserves in China are large, although shale gas production is still in its infancy. This paper reviews Chinese national policies and guidelines related to shale gas development, in particular those related to recent progress in the development of shale gas reserves in Sichuan Province and Chongqing since February 2015. In addition, three large-scale R&D projects related to shale gas development, funded by the Government of China, are introduced, and the scope of the work in each project is described.