Shale Gas In China Research Articles

Theoretical insights, core technologies and practices concerning “volume development” of shale gas in China

In recent years, major exploration breakthroughs and subsequent booming development of marine shale gas in both Upper Ordovician Wufeng and Lower Silurian Longmaxi Fms in the Sichuan Basin and its periphery highlight the strategic importance for the theoretical innovation and technological advances of gas in China. A number of key theories and technologies, such as continuous hydrocarbon accumulation and horizontal well volume fracturing, and so on, have contributed to the large-scale development of shale gas fields such as Shunan, Fuling, etc., in Sichuan Basin. Based on China's geological conditions, industrial practices and current limitations in executing the full-scale development of shale gas, a new concept called “volume development (VD)” has been proposed. Under the framework of this theory, man-made volumetric fracture network systems are established through the combination of horizontal well drilling and transverse hydraulic fracturing through which gas flow become much more efficient due to the lateral flow superimposed by vertical fracture flow. VD has become a very efficient development model for shale gas because it can make gas in the volume affected by the man-made fracture network system become commercial reserves, and be produced more cost-effectively. VD includes five core technologies, i.e. comprehensive evaluation of “sweet areas”, optimization design of well patterns for volume development, optimization and trajectory design of horizontal well drilling in target window, massive fracturing technology for horizontal wellbores, design of production system and platform-based well factory-like management. The VD theory and technology provides important theoretical basis and technical support not only for the present three-dimensional development of shale gas in Changning, Fuling and other nearby blocks, but for the overall utilization of unconventional oil and gas resources such as continental, transitional shale gas. It is believed that VD will have broad application prospects in shale gas development.

Reflections and suggestions on the development and engineering management of shale gas fracturing technology in China

Shale gas resource in China is greatly different from that in the North America in term of natural endowment, so North America's experience and practice of shale gas revolution shall not be copied blindly in China. In order to realize scale effective development of shale gas resource in China, we analyzed and summarized the status quo of domestic shale gas stimulation technologies referring to the advanced concepts of shale gas development in the North America, considering the actual situations of shale gas resource in China. Then, some suggestions were proposed on the development direction of key shale gas fracturing technologies and the enhancement of engineering management. First, a data volume that integrates geological, engineering and production information is the base for designing and optimizing all segments of shale gas exploration, development and production. Therefore, it is necessary to break the “data isolated island”, strengthen data mining and improve the data application efficiency, so as to promote the integration of geo-engineering data fusion. Second, the geomechanics test & evaluation method and technology suitable for shale reservoirs shall be developed and improved by taking into consideration the anisotropic mechanical behaviors and ground stress characteristics of shale reservoirs, so as to increase the design level of geo-engineering integration program. Third, it is necessary to develop the dissolvable bridge plug, improve operation the efficiency of staged fracturing and reduce the operation risk, so as to achieve cost reduction and benefit increase of shale gas development. Fourth, there is still great room for the improvement of the engineering management system, which is worth exploring and studying further. Therefore, oil & gas industry and companies shall seize this critical strategic opportunity to actively optimize the current engineering management pattern and seek the optimal approach to quality improving and benefit increasing. In conclusion, the exploration and development of shale gas in China is currently in the early stage and there is an obvious gap compared with foreign countries in terms of technology & equipment, production management, exploration and development achievement and policy & regulation. Therefore, it is in an urgent need to innovatively explore a way feasible for the actual shale gas development in China based on the resource conditions of its own after referring, digesting and absorbing the hydraulic fracturing experience and management concept of shale gas revolution in the United States.

Major progress in the natural gas exploration and development in the past seven decades in China

Abstract China has made significant progress in the exploration and development of natural gas in the past 70 years, from the gas-poor country to the world's sixth largest gas production country. In 1949, the annual gas output in China was 1 117×104 m3, the proved gas reserves were 3.85×108 m3, and the average annual gas consumption and available reserves of per person were 0.020 6 m3 and 0.710 7 m3, respectively. By 2018, the average domestic annual gas production per person was 114.857 6 m3 and the reserves were 12 011.08 m3, and the average domestic annual gas production and reserves per person in the past 70 years increased by 5 575 times and 16 900 times, respectively. The exploration and development of large gas fields is the main way to rapidly develop the natural gas industry. 72 large gas fields have been discovered in China so far, mainly distributed in three basins, Sichuan (25), Ordos (13) and Tarim (10). In 2018, the total gas production of the large gas fields in these three basins was 1 039.26×108 m3, accounting for 65% of the total gas production in China. By the end of 2018, the cumulative proved gas reserves of the 72 large gas fields had amounted to 124504×108 m3, accounting for 75% of the total national gas reserves (16.7×1012 m3). New theories of natural gas have promoted the development of China's natural gas industry faster. Since 1979, the new theory of coal-derived gas has boosted the discovery of gas fields mainly from coal-measure source rocks in China. In 2018, the gas production of large coal-derived gas fields in China accounted for 50.93% and 75.47% of the total national gas production and total gas production of large gas fields, respectively. Guided by shale gas theories, shale gas fields such as Fuling, Changning, Weiyuan and Weirong have been discovered. In 2018, the total proved geological reserves of shale gas were 10 455.67× 108 m3, and the annual gas production was 108.8×108 m3, demonstrating a good prospect of shale gas in China.

Approaches for the evaluation of favorable shale gas areas and applications: Implications for China's exploration strategy

AbstractTo explore practical approaches for the evaluation of favorable shale gas areas, a structural decomposition analysis with respect to the index system, evaluation criteria, weight determination, and evaluation methods was carried out. Five types of indexes were determined from 25 subindexes that formed the index system, and improved whitenization weight functions are proposed to establish evaluation criteria. The index weights calculated using entropy weight and Euclidean distance methods are consistent, whereas the weights determined by gray relational analysis are significantly affected by the relative number of indexes and evaluation objects, selected mother factor, and resolution coefficient. The significant linear positive correlation between the relative approach degree values calculated using TOPSIS and the scores obtained using fuzzy comprehensive evaluation (FCE) is indicative of a consistent evaluation result, but it should be noted that extreme indicator values can have strong effects on the evaluation using the fuzzy similarity method. Finally, an exploration strategy for China's shale gas is suggested: Areas with weak reformation and relatively low maturity are expected to be favorable for marine shale production in South China, and continental and transitional shale‐bearing basins are promising for the prospecting multiple‐origin shale gas and coal measure gas, respectively.

Life cycle greenhouse gas emissions of China shale gas

Having the largest shale gas reserve in the world, China is vigorously developing its shale gas resources. In this work, a hybrid life cycle inventory is used to estimate upstream greenhouse gas (GHG) emissions and evaluate the atmospheric environmental effects of China’s shale gas development. A comprehensive GHG emission model of the preproduction phase is constructed by considering green completion, methane emission from flowback water, indirect emissions from materials upstream material manufacturing, and Monte Carlo simulation. Results indicate that the upstream GHG emission of 230 shale gas wells is 18.8 g CO2eq/MJ. During the preproduction phase (from well pad preparation to well completion), indirect GHG emissions from upstream material manufacturing are substantial and account for 78%. The estimation of GHG emissions in preproduction phase presents considerable uncertainty (39%–79%) due to the uncertainty of constructing the pad preparation process and the estimated ultimate recovery. In preproduction phase, the GHG emission of China shale gas is estimated to be approximately 4.18 g CO2eq/MJ (95% CI: 2.57 to 7.47 g CO2eq/MJ), which is higher than that of the US shale gas.

Mechanism Analysis of Organic Matter Enrichment of Upper Ordovician-Lower Silurian Shale in the Upper Yangtze Area: Taking Jiaoye-1 Well in the Jiaoshiba Block as an Example

Organic matter is the material basis of shale hydrocarbon generation. The current organic matter content in shale is controlled by the original sedimentary organic matter abundance. Therefore, the study of the enrichment mechanism of sedimentary organic matter in shale has become an important issue to be solved. The Upper Yangtze area is the important exploration and exploitation area of marine shale gas in China. The shale of the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in the Yangtze area is the research object. Choosing redox indicator and biological productivity indicator, the study explores the enrichment mechanism of sedimentary organic matter from two aspects, sealing of water and volcanic activity. The results show that excess siliceous mineral in the shale of the Wufeng Formation-Longmaxi Formation in the Upper Yangtze area is bioorigin. Excess siliceous mineral can be used as one of the indicators of biological productivity. On the one hand, layer phenomenon occurred since the strong water sealing during the sedimentary period of Wufeng and the lower section of the Longmaxi Formation, which results in the high content of oxygen in surface water. On the other hand, the active volcanic activity brought volcanic ash which was beneficial to biological reproduction. Both of these factors led to higher biological productivity during this period. At the same time, the strong sealing of water made the lower layer of the water more reductive, and the active volcanic activity caused climate change, enhancing the reduction of the lower layer of the water, which made the rich organic matter deposited from the surface water well preserved. In the sedimentary period of the upper section of the Longmaxi Formation 1st member in the Upper Yangtze area, on the one hand, due to the weakened sealing of water, the oxygen content of the upper water decreased. On the other hand, the volcanic activity weakened until it stopped, and the source of volcanic ash rich in nutrient elements decreased. These two aspects led to lower biological productivity during this period. At the same time, the weaker water sealing could lead to a decrease in the reduction of the lower layer of the water, and the gradual cessation of volcanic activity no longer affected the climate, causing the destruction of sedimentary organic matter by oxidation.

Comprehensive Understanding of OM-Hosted Pores in Transitional Shale: A Case Study of Permian Longtan Shale in South China Based on Organic Petrographic Analysis, Gas Adsorption, and X-ray Diffraction Measurements

Marine-continental transitional (hereinafter referred to as transitional) Permian shales are the important targets for shale gas in China. However, the nature and formation of organic matter (OM)-h...

A Cause Analysis of the High-Content Nitrogen and Low-Content Hydrocarbon in Shale Gas: A Case Study of the Early Cambrian in Xiuwu Basin, Yangtze Region

There are successes and failures in the exploration of marine shale gas in South China. In some shale gas plays with great basis for hydrocarbon generation, a phenomenon exists that gas loggings reflect low gas bearing in some of the wells and the gas is dominated by nitrogen rather than hydrocarbon gas. The study of nitrogen concentration in shale gas contributes to solve the question that how shale gas diffuses in complex tectonic areas, which helps to figure out the preservation requirements and accumulation mechanisms of shale gas and avoid exploration crisis. This study focused on the lower Cambrian shale in Xiuwu Basin, Lower Yangtze Region, with emphasis on the well Jiangye-1, using gas component analysis, stable nitrogen isotope analysis, overburden permeability tests in parallel and perpendicular directions, and FIB-HIM experiments, also combining with core description, outcrop observation, and seismic interpretation to explore the causes of the high-content nitrogen and low-content hydrocarbon in the lower Cambrian shale gas. The results show that the nitrogen of the lower Cambrian shale in Xiuwu Basin is derived from the atmosphere and the deep crust-upper mantle. The bedding planes and the detachment layer at the bottom of the lower Cambrian compose the lateral pathways, and the widespread deep faults are the vertical pathways for shale gas migration and diffusion. Combining these two, an effective pathway network was built, favorable to gas exchange between the shale gas interval and the atmosphere, partly leading to the concentration of nitrogen and the diffusion of hydrocarbon gas. In the Jurassic, the magmatic activities occurred frequently in the surrounding areas, which not only brought nitrogen from the deep crust-upper mantle but also increased the value of paleo-heat flow even though the basin began to uplift, which promoted the graphitization of organic matter and the collapse of organic pores and accelerated the loss of shale gas. Based on the study above, an explanation model was summarized to expound the causes of high-content nitrogen and low-content hydrocarbon in shale gas plays near the plate-active region in Xiuwu Basin, Lower Yangtze Region.

Determination of critical parameters for evaluating coal measure shale gas in China

Coal measure shale is one of the most abundant types of marine-continental shales in China. Two sets of typical coal measure shales in China are developed in the Shanxi Formation (Ordos Basin) and in the Longtan Formation (Guizhou Province). In this study, thermal simulation, rock pyrolysis, and X-ray diffraction experiments were used to analyze four coal measure shale samples collected from typical areas of China. Based on the study of hydrocarbon generation process of the samples, the lower limits of thermal maturity (Ro) of favorable and target areas for coal measure shale were ∼1.8% and 2.5%, respectively. The threshold Ro value of oil generation in coal measure shale was preliminarily inferred to be 0.6%. The gaseous hydrocarbon production per unit of S1+S2, after the gas generation threshold, was linearly and positively correlated with Ro. The lower limits of total organic carbon (TOC), corresponding to the favorable and target areas, were ∼2.45 wt% and 2.84 wt%, respectively. Combined with X-ray diffraction experiments, the diagenetic stage and the hydrocarbon generation model of coal measure shale were established and could be divided into four evolutionary stages. The results of this study have direct scientific and practical significance for the evaluation of gas content and selection of areas in China for the extraction of coal measure shale.

Iterative Analytical Solutions for Nonlinear Two-Phase Flow with Gas Solubility in Shale Gas Reservoirs

The governing equations of a two-phase flow have a strong nonlinear term due to the interactions between gas and water such as capillary pressure, water saturation, and gas solubility. This nonlinearity is usually ignored or approximated in order to obtain analytical solutions. The impact of such ignorance on the accuracy of solutions has not been clear so far. This study seeks analytical solutions without ignoring this nonlinear term. Firstly, a nonlinear mathematical model is developed for the two-phase flow of gas and water during shale gas production. This model also considers the effects of gas solubility in water. Then, iterative analytical solutions for pore pressures and production rates of gas and water are derived by the combination of travelling wave and variational iteration methods. Thirdly, the convergence and accuracy of the solutions are checked through history matching of two sets of gas production data: a China shale gas reservoir and a horizontal Barnett shale well. Finally, the effects of the nonlinear term, shale gas solubility, and entry capillary pressure on the shale gas production rate are investigated. It is found that these iterative analytical solutions can be convergent within 2-3 iterations. The solutions can well describe the production rates of both gas and water. The nonlinear term can significantly affect the forecast of shale gas production in both the short term and the long term. Entry capillary pressure and shale gas solubility in water can also affect shale gas production rates of shale gas and water. These analytical solutions can be used for the fast calculation of the production rates of both shale gas and water in the two-phase flow stage.

What are the key barriers for the further development of shale gas in China? A grey-DEMATEL approach

The evaluation and analysis of barriers that restrict the large-scale development of shale gas are beneficial to the selection of a scientific and reasonable development model. The objective of our study was to reveal the key barriers to the large-scale development of shale gas in China. Sixteen barriers were identified by adopting literature reviews and expert interviews, and the grey-based Decision-Making Trial and Evaluation Laboratory (grey-DEMATEL) approach was adopted to analyze the barriers based on the sample data obtained from a questionnaire of senior experts in China’s shale gas industry. The results showed that high development costs, lack of experience, lack of technology transfer between enterprises, risk of environmental pollution, lack of key technologies, and lack of capability in investment and risk resistance are the key barriers to the further development of shale gas in China. We put forward some policy suggestions based on these results.

Study on Optimal Economic Evaluation of Industrial Drilling Platform for Shale Oil and Gas Development

The development of shale oil and gas in China is at a critical stage, and the technology of factory drilling platforms, as the key technology of shale oil and gas development in North America, is worthy of in-depth study on its function, optimization mode and economic evaluation in China’s shale oil and gas development industry. The number of wells and the operation mode of factory drilling platforms will directly affect the economics of factory drilling platform technology, but there is a lack of technical and economic evaluation models of such platforms. Therefore, by analyzing the application of factory drilling platforms and the international advanced design method, a technical and economic evaluation model is established, and data from the Sichuan Shale gas field are calculated and analyzed. The research shows that the proposed economic evaluation and analysis method, and the calculation of the optimal number and operation mode of factory drilling platforms, can provide guidance for the overall deployment and design of this technology, and some relevant suggestions are proposed in the light of the problems related to the use of these platforms by Chinese oil and gas companies.

Logging evaluation of free-gas saturation and volume content in Wufeng-Longmaxi organic-rich shales in the Upper Yangtze Platform, China

Abstract The Wufeng-Longmaxi shale is the most important target for the exploration and production of shale gas in China. There are two important parameters of great importance to shale gas evaluation: free gas saturation and content. However, current models that have been proposed based on the use of sandstone are not applicable to this shale gas reservoir due to differences in conductivity mechanisms between these two types of reservoirs. In this study, after the pore volume of gas shale had been classified into three phases, those being the adsorbed phase pore, free phase pore, and bound water pore, we proposed a method to calculate the free gas saturation and content from well logging data based on the pore volume model. Our method utilizes the following procedures: 1) determining the total porosity on the basis of the matrix value of dry clay; 2) establishing a quantitative correlation of the bound water content to the clay content and then determining the bound water porosity; 3) calculating the absorbed gas content by Langmuir formula; 4) calculating the adsorbed phase porosity according to the principle of mass conservation after determining the underground density of the adsorbed phase (in the range of 0.4–1.2 g/cm3); and 5) determining the free gas saturation and free gas content. Field examples show that the predicted shale porosity, free gas, and adsorbed gas contents calculated by using our proposed model accurately coordinate with the core derived results, which verified that the proposed method was valuable to evaluating the Wufeng-Longmaxi shale gas reservoir.

Analysis of influence factors of methane adsorption capacity of the Lower Silurian shale

The Lower Silurian marine shale gas in South China has great potential. In order to study the influence factors of methane adsorption capacity of the marine shale in Sangzhi block, six samples from the Lower Silurian were investigated by a series of experiments. The total organic carbon (TOC) content ranges from 1.97 to 3.49% and organic matter are in the state of over-maturity. The dominant mineralogical compositions are quartz and clay minerals. The methane adsorption capacity of the studied shale ranges from 1.5627 to 2.2033 cm3/g, and is mainly influenced by the TOC content.

Evolution and migration of shale facies and their control on shale gas: A case study from the Wufeng-Longmaxi Formations in the Sichuan Basin and its surroundings

The Fuling gas field, the largest commercial discovery of shale gas in China, has been producing from the organic-rich shale in the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation in the Sichuan Basin, China. A refined shale gas E&P and sweet spots identification require studies to be carried out not only at the sedimentary facies scale but also at the petrographic scale. This paper focuses on the characteristics of organic-rich shales. Based on data from outcrops, drilling cores, X-ray diffraction, thin sections, and scanning electric microscope, a systematic analysis of wells and well-correlation sections indicates that shales in the study area underwent two progressive and regressive cycles. In addition, differences in lithofacies and their organic or inorganic components are significant either in the vertical or in the horizontal direction, which generally controls the material basis of shale gas. The early-stage siliceous shale distributes in the east, whereas the late-stage carbonate-bearing shale extends to the west. In the southeastern Sichuan Basin, the siliceous composition decreases, whereas the clay minerals increase upward. In the central Sichuan uplift, there is a higher carbonate content. And with our new lithofacies maps, distribution of the sweet spots was identified. The northeastern Sichuan Basin has the siliceous shale in the Wufeng Formation and the silicon-bearing shale in the Longmaxi Formation, making it a play area with the greatest gas potential. The southern Sichuan Basin occurs as a favorable lithofacies area with the stacked siliceous shale in the Wufeng Formation and the calcareous shale in the Longmaxi Formation. The relatively favorable lithofacies area covers the regions extending from the periphery of southern Sichuan Basin toward the central Sichuan uplift and the northern Guizhou uplift, featuring stacked carbonate-bearing shale and clay mineral-bearing shale in the Longmaxi Formation. The shallow-marine areas close to the uplifts are dominated by mudstone and silty mudstone, thereby possessing poor material basis.

Present Situation of China's Shale Gas Exploration and Development

Present Situation of China's Shale Gas Exploration and Development

The lay of the land: The public, participation and policy in China’s fracking frenzy

This perspective paper examines the current policy landscape for hydraulic fracturing in China, with a focus on the role of public attitudes toward shale gas in China. We highlight the need for further research on public perceptions and responses in a non-democratic society, both for the potential protection of residents who might be affected by the technology as well as the valuable research data that can be contrasted with public perspectives and engagement in other countries.Although the empirical findings presented here are limited due to this being very preliminary research, our goal is to shed light on what existing data shows about current understanding and perceptions. We discuss preliminary data collected during a research trip to Beijing in late December 2017, and contrast it with the few empirical studies on China that exist to date (Sher and Wu, 2018; Yu et al., 2018). Our research demonstrates the need for further investigation of understanding and perceptions of shale gas in China, particularly as other countries (such as the United Kingdom and Poland) are beginning to look at expanding their own shale gas resources. A reflection on this will also lead to a discussion of the extent to which data from China does or does not relate to that from other nations.

Water use for shale gas extraction in the Sichuan Basin, China

This study investigates the use of water for extracting shale gas in the Sichuan Basin of China. Both net water use and water intensity (i.e., water use per unit of gas produced) of shale wells are estimated by applying a process-based life cycle inventory (LCI) model. The results show that the net water use and water intensity are around 24500 m3/well and 1.9 m3 water/104 m3 gas respectively, and that the fracturing and completion stage of shale gas extraction accounts for the largest share in net water use. A comparison shows that China's water use for shale gas extraction is generally higher than that of other countries. By considering the predicted annual drilling activities in the Sichuan Basin, we find that the annual water demand for shale gas development is likely to be negligible compared to total regional water supply. However, considering the water demand for shale gas extraction and the water demand from other sectors may make water availability a significant concern for China's shale gas development in the future.

China's shale gas exploration and development: Understanding and practice

Through detailed analyses of the distribution characteristics of organic-rich shale, appearance features of high-quality shale, microscopic characteristics of shale reservoir rocks, fracability, and the relationship between preservation conditions and shale gas enrichment in Upper Ordovician Wufeng Formation−Lower Silurian Longmaxi Formation in Sichuan Basin, theoretical understandings and specific suggestions with respect to the exploration and development of shale gas in China are summarized and proposed respectively. Important geological understandings in the exploration and development of shale gas of the Wufeng Formation–Longmaxi Formation in the Sichuan Basin can be summarized into the following aspects: depositional environment and depositional process control the distribution of organic-rich shale; high quality shale in “sweet spot segments” are commonly characterized by high content of organic carbon, high brittleness, high porosity and gas content; organic pores are important storage space for the enrichment of shale gas; preservation conditions are the key factor for the geological evaluation of shale gas in structurally complex regions; shale gas can be considered as “artificial gas reservoirs” and the fracability assessment is essential for high-production; nanoscale storage space and the mode of occurrence control the special seepage characteristics of shale gas. The following suggestions are proposed for the development of China's shale gas industry: (1) focus more on fundamental research to achieve new breakthrough in the geological theory of shale gas; (2) emphasize exploration practices to have all-round discoveries in multiple strata; (3) study the regularities of development and production to establish new models of shale gas development; (4) think creatively to invent new technologies to tackle key problems; (5) explore the management innovation to create new mechanisms in shale gas development.

Gas production peaks in China: Research and strategic proposals

The peaks of natural gas production are of great significance to the planning of national energy strategy, the coordinated development of natural gas industry chain and the investment decision-making for oil and gas companies. Therefore, based on natural gas geological and development characteristics, the production peaks of conventional gas (including tight gas), CBM and shale gas in China have been systematically analyzed and forecasted using multiple methods. The following conclusions are drawn: first, the cumulative gas production in China will reach 280–330 bcm by 2035 and 330–410 bcm by 2050; second, the conventional gas production peaks will be easily predicable during the forecast period, while the peaks of CBM and shale gas production need to be further forecasted and tracked continuously; third, with the possible breakthrough of gas hydrate exploration and development being considered, gas production in China has a great potential and bright future. In order to achieve a strategic goal of energy transformation and conservation and to guarantee a safe and stable gas supply, a timely profound analysis and study will be necessary on the international political, economic and energy development situation for a global gas strategic layout. In view of this, based on the analysis of domestic natural gas supply and demand situation, the following proposals are put forward: to speed up the domestic tapping and commercial production of those deep-strata, deep-water and unconventional gas resources to consolidate the dominant position of domestic natural gas supply; to attach great importance to a strategic layout of overseas gas resources utilization and to adopt various ways to ensure the security of domestic gas market; to accelerate the evaluation of gas hydrate development in order to enlarge and consolidate the gas resource basis; and to strengthen a dynamic forecast on the peaks of gas production in order to continuously enhance the soft power in international competition.