Sichuan Basin Of China Research Articles

A pragmatic approach for identifying effective lacustrine shale payzones

Compared with the marine shale payzones, lacustrine shale payzones generally contain more interbed layers (e.g., sandstone interbeds and carbonate interbeds), bringing about a higher complexity to the identification of effective lacustrine shale payzones. In this work, a pragmatic but systematic approach is developed to identify the effective lacustrine shale payzones with commercial hydrocarbon-production potentials. Such identification approach is developed based on three easily accessible data sources that are obtained from multiple wells drilled in a given region: 1) well logging data; 2) measured properties of the core samples; and 3) production test data. In this approach, the first step is to identify shale-containing formations based on the lithology profile along a well that has been interpreted using the well logging data. Secondly, a shale-dominated formation is extracted from a given shale-containing formation if the ratio of total shale thickness to the total formation thickness exceeds 60%; this cut-off value is selected based on the consideration that such formation has a higher possibility of industrial production potential. Lastly, a shale-dominated formation can be classified as an effective shale payzone if the total organic carbon (TOC) content, porosity, and effective thickness are all greater than the given threshold values. By using this proposed method, one can obtain the total effective thickness and the regional distribution of effective lacustrine shale payzones, which could help to locate the sweet spot of the shale payzones as well as subsequently design proper methods for recovering the shale resources. The Lower Jurassic formations possess abundant lacustrine shale layers that are widely considered to be the potential lacustrine shale gas payzones in the northwest of Sichuan Basin in China. A case study in this formation is presented to demonstrate the efficacy of the newly developed approach in identifying the effective lacustrine shale payzones. Validation results prove that this new method can be used to effectively identify the effective lacustrine shale payzones with commercial production potentials.

Pre-stack seismic density inversion in marine shale reservoirs in the southern Jiaoshiba area, Sichuan Basin, China

For a typical marine shale reservoir in the Jiaoshiba area, Sichuan Basin of China, P-impedance is sensitive for identifying lithology but not suitable for indicating good shale reservoirs. In comparison, density is an important quantity, which is sensitive for identifying the organic-rich mud shale from non-organic-rich mud shale. Due to the poor data quality and incidence angle range, density cannot be easily inverted by directly solving the ill-posed pre-stack seismic inversion in this area. Meanwhile, the traditional density regularizations implemented by directly using the more robust P-impedance inversion tend to be inaccurate for recovering density for this shale reservoir. In this paper, we combine the P-impedance and the minus uranium to construct the pseudo-P-impedance (PIp) at well locations. The PIp is observed to be sensitive for identifying organic-rich mud shale and has a good correlation with density in this area. We employ the PIp–density relation into the pre-stack inversion framework to estimate density. Three types of regularization are tested on both numerical and field data: These are no regularization, traditional regularization and the proposed approach. It is observed that the proposed method is better for recovering the density of organic-rich mud shale in the Jiaoshiba area.

Experimental investigation of fracture propagation induced by carbon dioxide and water in coal seam reservoirs

Because of the low or ultra-low permeability of coal seams, hydraulic fracturing technology has been widely used to improve the permeability of coal seams in both ground and underground extraction. Recently, liquid carbon dioxide (L-CO2) as an environment-friendly fracturing fluid has drawn attention from researchers and engineers. In this study, a true tri-axial system was adopted to perform hydraulic and L-CO2 fracturing experiments on coal specimens from the South Sichuan Basin in China. The effects of geological and engineering factors (horizontal stress ratio, injection rate, and fracturing fluid) on induced fracture propagation were investigated in this study. The various geological and engineering factors can synthetically, rather than unilaterally, impact the fractures propagation to generate three types of stimulation mechanism. Based on our experimental results, we succeeded in approximately predicting the stimulation mechanism for induced fracturing under different conditions. Generally, the effect of pre-existing natural fractures on the fracture propagation was enhanced, whereas the effect of the geo-stress was reduced, when L-CO2 was adopted as the fracturing fluid.

Shale gas reservoir characterization: A typical case in the Southeast Chongqing of Sichuan Basin, China.

The Lower Silurian Longmaxi Shale in Southeast Chongqing of Sichuan Basin in China is considered to be a potential shale gas reservoir by many scholars in recent years. The special shale gas well, namely, Pengye-1 well, was selected as a case study to evaluate the characteristics of the shale gas reservoir. A series of experiments were performed to analyze the geochemical, mineralogical, and petrophysical features and gas content using samples of the Longmaxi Shale from Pengye-1 well. The results show that the organic and inorganic porosities of these samples are range of 0.08–2.73% and 0.06–2.65%, with the average of 1.10% and 1.76%, respectively. The inorganic pores primarily contribute to the porosity until the TOC content is more than 3%. Organic matter plays an important role in adsorbed gas content. The adsorbed gas is dominant in the Longmaxi Shale of Pengye-1 well, which ranges from 0.46 to 2.24 cm3/g, with an average of 1.38 cm3/g. The free gas content ranges from 0.45 to 0.84 cm3/g with an average of 0.68 cm3/g, and is 24.4–49.7 percent of total gas with an average of 37.5%. The bottom part of the Longmaxi Shale is the most favorable for shale gas exploring, which is higher of brittleness mineral content, porosity and gas content. Compare with the other five shales in America, the Lower Silurian Longmaxi Shale is derived from older sedimentary periods with significantly higher thermal maturity and has experienced several periods of intense tectonic, which are unfavorable for the shale gas enrichment.

Contribution of soil fauna to the degradation of recalcitrant components in Cinnamomum camphora foliar litter in different-sized gaps in Pinus massoniana plantations

Forest gaps are important in forest dynamics and management, but little is known about how soil fauna influence the degradation of recalcitrant litter components in different-sized forest gaps. This investigation uses litterbags with two different mesh sizes (0.04 and 3 mm) to control the meso- and microfauna entering the bags to quantify the contribution of soil fauna to the degradation of recalcitrant components (including condensed tannins, total phenol, lignin and cellulose) during litter decomposition. The experiment was conducted in seven different forest gap sizes in Pinus massoniana plantations over 1 year. One closed-canopy site (CC) and forest gap sizes of 100, 225, 400, 625, 900, 1225 and 1600 m2 were created in a P. massoniana plantation in the Sichuan basin of China; the CC was treated as the control. Cinnamomum camphora foliage from local native trees was used in all forest gap experiments. We found the following: (1) Gap size had significant effects on the degradation rates (E) of condensed tannins and lignin and on the contributions of soil fauna; medium-sized gaps also presented high degradation rates. Soil fauna obviously contributed to the degradation of recalcitrant foliar litter components in medium-sized gaps. (2) The highest contribution to degradation (40.98%) was recorded for lignin, and the lowest contribution (0.29%) was recorded for condensed tannins. The results indicate that medium-sized gaps (900 m2) were conducive to the degradation of recalcitrant litter components by soil fauna.

Analysis and countermeasures on sustained casing pressure in b-annulus of shale-gas horizontal wells in Sichuan basin of china

In Sichuan Basin of China, the percentage of shale gas wells with sustained casing pressure (SCP) is high, bringing about challenges to the efficient development of gas reservoirs and the wellbore integrity of gas wells. In this paper, the actual SCP situa­tions in domestic shale gas development blocks were analyzed specifically. The gas source was determined by using the isotope analysis method, and SCP mechanisms of shale gas wells were studied by means of physical simulation experiment. Accordingly, the failure laws of cement sheath in different cement slurry systems in the process of fracturing were figured out, and the key technologies of improve the sealing capacity of cement sheath and relieve the SCP phenomenon in staged fracturing wells were developed. On the premise that the cement slurry column can structurally satisfy the sealing requirement completely, a cement slurry system of low porosity and low elastic modulus was developed by means of the interphase filling technique and the set cement porosity decreasing method. The elastic modulus was only 4.2 GPa, the porosity was as low as 27.1% (the porosity of conventional cement stone is 35.0%), and the elastic deformation capacity of cement stone was en­hanced dramatically. The new cement slurry system has been practically applied in 5 wells, and the high-quality cementing rate was 100% with no SCP. This research provides useful reference for SCP control.

Fractal Characteristics of Lacustrine Tight Carbonate Nanoscale Reservoirs

The complexity and heterogeneity of pore structure greatly affect gas-liquid accumulation and transport, and the fractal theory has been proven to be an effective approach for studying nanoscale reservoirs in shale, coal, and tight sandstones. However, researches on fractal characteristics and control mechanisms for the lacustrine tight carbonate have received little attention. Lacustrine tight carbonate samples from the Jurassic Da’anzhai Member in the Sichuan Basin in China were systematically investigated focusing on the fractal characteristics and control mechanisms of storage spaces, minerals, diagenesis, and paleoenvironments. The fractal dimensions can be separated into two different and valid parts including D1 (2.515–2.785, average 2.652) and D2 (2.424–2.562, average 2.485), and the correlation between them is negative rather than positive. The average pore diameters exhibit a positive correlation with D1 and a negative correlation with D2, and the storage space is positively correlated with D2 a...

A semi-analytical model to evaluate productivity of shale gas wells with complex fracture networks

With the increasing of clean energy demands and the maturing of shale gas extraction technology, multiple fractured horizontal well (MFHW) has become the most key technology for shale gas development. After hydraulic fracturing, fracture networks, which consist of natural fractures, hydraulic fractures and secondary fractures, are formed around the wellbore. Compared to conventional gas reservoirs, shale gas reservoirs are characterized by the complex fracture networks and gas adsorptions in shale matrix. Therefore, it is essential to propose a new productivity evaluation method for shale gas wells to handle these characteristics.In this paper, to account for special characteristics of MFHW, a complex fracture model for shale gas reservoirs is established. With the new method, shale reservoirs are depicted by De Swaan dual porosity model, where the secondary fractures and hydraulic fractures are characterized by discrete units. Therefore, together with micro-seismic data, fracture networks can be exactly described using this new model. With a well-depicted facture network, Green function and superposition method are then adopted to model the flow in the reservoir, and finite difference method is used to solve the equations of one-dimensional flow in fracture system. Besides, to deal with the complex flow in the fracture intersection, star-delta transformation is applied Finally, the equations of reservoir and fracture system, the solution in Laplace domain is obtained, which can then be transferred to real domain using the Stehfest algorithm.Comparisons were made between the results of the proposed model and that of a numerical model accomplished by commercial simulator Eclipse for a specific case to verify the accuracy of the model. Results show that the semi-analytical method is more efficient than numerical method by reducing the computing time without losing accuracy. Moreover, the semi-analytical productivity evaluation method can describe fracture networks more exactly. Then, a field case from Sichuan Basin of China is applied in the analysis. The results shows that desorption gas takes up 10%-30% of the total production in this case. Besides, the effects of storage capacity ratio and inter-porosity flow coefficient on type curves were analyzed based on the production decline curves. In addition, pressure profiles of different production times are obtained by the superposition of pressure potential.

Reservoir quality, natural fractures, and gas productivity of upper Triassic Xujiahe tight gas sandstones in western Sichuan Basin, China

The main target for hydrocarbon exploration in the western Sichuan Basin in China is the tight gas sandstone reservoir of the Upper Triassic Xujiahe Formation. Sandstones of the Xujiahe Formation are characterized as tight with ultralow porosity, ultralow permeability, and intensive heterogeneity. In this study, various techniques, such as scanning electron microscopy, X-ray diffraction, cathodoluminescence microscopy, casting thin-section, and fluid inclusion thermometry, were employed to investigate the composition, sedimentary facies, diagenesis history, diagenetic intensity, natural fracture characteristics, and their impact on reservoir quality. The results showed that subaqueous distributary channels and mouth bars with low rock fragment content are favorable for pore preservation and secondary pore development. Except for the medium to strong dissolution intensity, chlorite rim growth is also important for the development of high quality reservoirs. Intraformational shear fractures and horizontal shear fractures associated with tectonic movement increase pore space and improve the capability of transmitting fluids. Differences in gas productivity could be attributed to differences in reservoir quality, which were controlled by the sedimentary environment, diagenetic intensity, and fracture characteristics. A significantly positive correlation was found between total porosity and gas productivity of the tight sandstones. The high density fracture distribution was found owing to the fault system and structural deformation zone, which resulted in high gas productivity. The research results were successfully applied to improve production efficiency in the Xujiahe tight gas sandstones, and could be applicable to other similar fields involving tight gas.

Investigation of drill-in fluids damage and its impact on wellbore stability in Longmaxi shale reservoir

The stability of the horizontal long section wellbore is the key factor of restricting the efficient development of shale gas. High clay mineral content and developed microfractures of shale reservoir make the problems of formation damage and horizontal wellbore stability more complex. OBDF (Oil-based drill-in fluid) is widely used to control formation damage and prevent wellbore instability in shale gas wells. However, high cost and serious environmental problem severely restrict the economic development of shale gas. In order to meet the requirement of cost reduction and environmental protection during shale gas drilling operation, drilling horizontal well with WBDF (water-based drill-in fluid) instead of OBDF has become one of the engineering technology problems to be solved urgently. The Longmaxi shale in Sichuan Basin of China and the associated drill-in fluids at the site are the object of our research. Evaluation experiments on liquid damage and sealing capacity of drill-in fluids were conducted to recognize and optimize the properties of oil-based and water-based drill-in fluids in shale reservoir. Combining the methods of particle size distribution, friction coefficient testing, alkali erosion, linear expansion and immersion test, we investigated the effect of drill-in fluids on formation damage and wellbore stability. Results show that the damage degree of OBDF filtrate on shale is more severe than that of WBDF filtrate. Fracture sealing and bi-directional pressure containment capacity of WBDF is also stronger than that of OBDF. Due to the invasion of OBDF with high pH value, the friction strength of the fracture surface decreases and frictional sliding will take place, which can cause the wellbore instability. With the WBDF immersion, microfractures initiate and propagate along the bedding surface for the shale hydrate expansion, and lead to wellbore instability. The results of our analysis suggest that OBDF does not completely solve the problems of formation damage and wellbore instability in shale reservoir, and reinforcing the sealing fracture and inhibiting hydration capacity of WBDF will contribute to its wider application in shale reservoir. This study provides a theoretical guidance for drill-in fluid selection and optimization during the operation of shale gas well drilling.

3D Full-Field and Pad Geomechanics Models Aid Shale Gas Field Development in China

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper IPTC 18984, “Three-Dimensional Full-Field and Pad Geomechanics Modeling Assists Effective Shale Gas Field Development, Sichuan Basin, China,” by Liang Xing, PetroChina; Xian Chenggang, SPE, Schlumberger; Shu Honglin, PetroChina; Chen Xin, Schlumberger; Zhang Jiehui, PetroChina; Wen Heng, Schlumberger; Wang Gaocheng, PetroChina; and Wang Lizhi, Guo Haixiao, Zhao Chunduan, Luo Fang, and Qiu Kaibin, SPE, Schlumberger, prepared for the 2016 International Petroleum Technology Conference, Bangkok, Thailand, 14–16 November. The paper has not been peer reviewed. Copyright 2016 International Petroleum Technology Conference. Reproduced by permission. The oilfield-development plan (ODP) for a shale gas field at the southern edge of the Sichuan Basin in China started in early 2014. The first wells drilled in the field and its adjacent blocks experienced significant challenges, such as severe mud losses, stuck tools, losses in the hole, high treating pressure, and unexpected screenout. Because an accurate understanding of geomechanics and its roles at various scales is vital, 3D full-field and pad geomechanics models were developed for achieving efficiency and effectiveness in implementing the ODP. Introduction The Ordovician-Silurian Wufeng-Longmaxi hot shale is an emerging shale gas play in China. Currently, the major exploration and development activities of the play are in the Sichuan Basin and its adjacent areas. For shale gas development in the Sichuan Basin and its adjacent areas, using the megascale, high-density, and continuous and regular pad drilling as is used in North America is difficult because surface and subsurface conditions are significantly different from those of the well-known North American shale plays. The strong environmental and social constraints that typify the Sichuan Basin and surrounding area are shown in Fig. 1. Drilling pads for shale gas developments are commonly located in narrow valleys that are often home to farmland and residential villages with dense populations. Differences of elevation among neighboring pads can be from several hundred meters to more than 1000 m. To speed up development of marine shale gas in the Sichuan Basin and its adjacent areas with a minimized learning curve, a geoscience-to-production integration of research, engineering, and operation with its associated research and development, methodologies, and work flows must be applied. This geoscience-to-production integration aims to optimize both efficiency and effectiveness dynamically at single-well, pad, and field scales with systematic and continuous optimization of technologies and solutions and the accumulation of knowledge and experience to enhance well productivity. One shale gas field, which is the study area of this paper, is in the mountainous area at the southern edge of the Sichuan Basin. The first wells drilled in this field and its adjacent blocks experienced significant geomechanics-associated challenges, such as severe mud losses, tools or drillingpipe sticking, losses in the hole, high treating pressure while hydraulic fracturing, and unexpected screen out of fracturing stages. Having reliable yet evolving understanding of geomechanics and its role at various scales during the progress of the ODP is vital. This paper describes the development of 3D full-field geomechanics models and high-resolution 3D pad geo-mechanics models and their engineering applications.

Ground-based measurement of column-averaged mixing ratios of methane and carbon dioxide in the Sichuan Basin of China by a desktop optical spectrum analyzer

Remote sensing of the atmospheric greenhouse gases, methane (CH4) and carbon dioxide (CO2), contributes to the understanding of global warming and climate change. A portable ground-based instrument consisting of a commercially available desktop optical spectrum analyzer and a small sun tracker has been applied to measure the column densities of atmospheric CH4 and CO2 at Yanting observation station in a mountainous paddy field of the Sichuan Basin from September to November 2013. The column-averaged dry-air molar mixing ratios, XCH4/XCO2, are compared with those retrieved by satellite observations in the Sichuan Basin and by ground-based network observations in the same latitude zone as the Yanting observation station.

Swelling of Shales: A Multiscale Experimental Investigation

Shale swelling can cause a series of problems during the exploitation of shale gas. However, because of the complex fabric of shale, a thorough understanding of shale swelling has not been gained. In this work, an experimental multiscale approach is employed to characterize the swelling properties of a shale sample from Sichuan basin of China. Wetting/drying tests are performed by environmental scanning electron microscopy (ESEM), and deformation of the material is measured by analyzing the ESEM micrographs using digital image correlation (DIC) techniques. Investigations are conducted at three distinct scales, enabling the macroscopic behavior to be linked to the microscopic mechanisms (e.g., the role of inclusions, the behavior of clay particles). The macroscopic swelling of the tested shale is less than 2%. This limited swelling is mainly due to the presence of nonswelling inclusions as well as the low swelling capacity of the clay inside the shale. Microcracking is evidenced along both the wetting and ...

Significance of gypsum-salt rock series for marine hydrocarbon accumulation

With further exploration and research, the gypsum-salts rock series as good caprocks attracted a lot of attention. The gypsum-salt rock series played an important role during migration, preservation and trapping of hydrocarbons. Recently, major breakthroughs have been continuously made in marine petroleum exploration of gypsum-salt rock series in the eastern Ordos Basin, the central Tarim Basin and the western Sichuan Basin in China, and the high-evolution and low-abundance gypsum-salt rock series as hydrocarbon source rocks become possible. Besides research advances in the reservoir–caprock assemblage of gypsum-salt rock series, development and hydrocarbon-generation potential of source rocks in the gypsum-salt rock series were well studied in terms of source-rock development environment and hydrocarbon generation mechanism. Results showed that the gypsum-salt rock series, including high-evolution and low-TOC gypsum-salt rock series in China, could be regarded as good source rocks. This understanding was a breakthrough to previous traditional viewpoint that low-TOC gypsum-salt rock series could not act as effective hydrocarbon sources. The key to understand hydrocarbon-generation mechanism was that abundant and high-quality hydrocarbon-generation materials, large amount of hydrocarbon generation and conversion in geological history, and hydrocarbon-generation materials occurred in the form of carboxylates, were developed in the high-evolution and low-TOC gypsum-salt rock series.

DNA barcoding-based sexual association of Sovia lucasii and S. lii (Lepidoptera: Hesperiidae), with description of a new subspecies.

Both sexes of two sympatric and sexually dimorphic species, Sovia lucasii (Mabille, 1876) and S. lii Xue, 2015, are associated based on DNA barcoding using the COI (mitochondrial cytochrome coxidase I) gene. The females are thus identified for the first time, and their wing patterns and genitalia are described and illustrated for the convenience of morphological identification hereafter. A new subspecies, S. lucasii minor ssp. nov., from the northeastern and eastern parts of the Sichuan Basin of China, is reported. External and genital differences between the new taxon and the nominate subspecies, which is distributed in western Sichuan and newly discovered in northwestern Guangxi, are illustrated and discussed.

The hazard risk assessment of regional heavy rainfall over Sichuan Basin of China

In this study, predictors for regional disastrous rainfall events over Sichuan Basin and a conceptual model for assessing their associated hazard risk levels are developed using 104 daily rain gauge observations during the 43-year period of 1961–2013. An analysis of 636 regional disastrous rainfall events reveals that their daily mean, daily maximum, area coverage, and duration could be adopted as critical hazard predictors in a conceptual model for assessing their associated risk levels. Such a conceptual model is then constructed after performing some statistical analyses through normal distribution function, interval displacement processing, correlation coefficient and weighting as well as Euclidean distance functional calculations. Since this model has obvious resolvability to grading the regional disastrous rainfall events and since it is highly consistent with the number of heavy rainstorms recorded over Sichuan Basin, it has a great potential to be applied to operational heavy rainfall forecasts and the associated hazard risk assessments in the future.

Characterization of shale gas enrichment in the Wufeng Formation–Longmaxi Formation in the Sichuan Basin of China and evaluation of its geological construction–transformation evolution sequence

Shale gas in Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation in the Sichuan Basin is one of the key strata being explored and developed in China, where shale gas reservoirs have been found in Fuling, Weiyuan, Changning and Zhaotong. Characteristics of shale gas enrichment in the formation shown by detailed profiling and analysis are summarized as “high, handsome and rich”. “High” mainly refers to the high quality of original materials for the formation of shale with excellent key parameters, including the good type and high abundance of organic matters, high content of brittle minerals and moderate thermal evolution. “Handsome” means late and weak deformation, favorable deformation mode and structure, and appropriate uplift and current burial depth. “Rich” includes high gas content, high formation pressure coefficient, good reservoir property, favorable reservoir scale transformation and high initial and final output, with relative ease of development and obvious economic benefit. For shale gas enrichment and high yield, it is important that the combination of shale was deposited and formed in excellent conditions (geological construction), and then underwent appropriate tectonic deformation, uplift, and erosion (geological transformation). Evaluation based on geological construction (evolution sequence from formation to the reservoir) includes sequence stratigraphy and sediment, hydrocarbon generation and formation of reservoir pores. Based on geological transformation (evolution sequence from the reservoir to preservation), the strata should be evaluated for structural deformation, the formation of reservoir fracture and preservation of shale gas. The evaluation of the “construction - transformation” sequence is to cover the whole process of shale gas formation and preservation. This way, both positive and negative effects of the formation-transformation sequence on shale gas are assessed. The evaluation models based on this strategy would be more accurate, reliable and would avoid bias derived from indiscriminate and simplistic use of all parameters in the models.

Assessing the feasibility and CO2 storage capacity of CO2 enhanced shale gas recovery using Triple-Porosity reservoir model

The depletion of conventional energy sources is leading to increased demand for unconventional energy sources. Shale gas is an important unconventional energy source that has been successfully developed and utilized in the United States. CO2 enhanced shale gas recovery (CO2-ESG) is a promising shale gas extraction technology. Supercritical CO2 injection can enhance the shale gas recovery through competitive absorption between the methane and the CO2 while also providing CO2 geological sequestration. However, assessments of the feasibility of CO2 enhanced shale gas recovery in field scale trials is quite complicated given the complex pore structures in shale reservoirs and the ultralow permeability. This paper describes a triple porosity, dual permeability (TP-DK) model that includes the effects of the shale gas adsorption and desorption, the competitive adsorption and binary gas diffusion. The Sichuan basin in China is selected as the target reservoir. The key parameters in this simulation were determined by experimental measurements of shale samples from the Lower Silurian Longmaxi Formation (LSLF) shale in the Sichuan basin. The results show that the CO2 injection can significantly enhance the shale gas recovery. A 90m thick shale gas reservoir with a 1200m horizontal well absorb injections of CO2 captured from a large 1000 MWe coal-fired power plant for 2years. However, the volume flow rate of the CO2 sequestration decreased with time as the production pressure decreased. Both the production time and the production pressure should be considered on the synergy between the CO2 sequestration and the shale gas recovery.

Analysis of the Influencing Factors on the Well Performance in Shale Gas Reservoir

Due to the ultralow permeability of shale gas reservoirs, stimulating the reservoir formation by using hydraulic fracturing technique and horizontal well is required to create the pathway of gas flow so that the shale gas can be recovered in an economically viable manner. The hydraulic fractured formations can be divided into two regions, stimulated reservoir volume (SRV) region and non-SRV region, and the produced shale gas may exist as free gas or adsorbed gas under the initial formation condition. Investigating the recovery factor of different types of shale gas in different region may assist us to make more reasonable development strategies. In this paper, we build a numerical simulation model, which has the ability to take the unique shale gas flow mechanisms into account, to quantitatively describe the gas production characteristics in each region based on the field data collected from a shale gas reservoir in Sichuan Basin in China. The contribution of the free gas and adsorbed gas to the total production is analyzed dynamically through the entire life of the shale gas production by adopting a component subdivision method. The effects of the key reservoir properties, such as shale matrix, secondary natural fracture network, and primary hydraulic fractures, on the recovery factor are also investigated.

Insights Into the Morphology of the East Asia PM2.5 Annual Cycle Provided by Machine Learning.

The abundance of airborne particulate matter with an aerodynamic equivalent diameter of 2.5 µm or less (PM2.5) is a significant environmental and health issue. Many tools have been used to examine the relationship between PM2.5 abundance and meteorological variables, but some of the relationships are nonlinear, non-Gaussian, and even unknown. Machine learning provides a broad range of practical algorithms to help examine this issue. In this study, we use machine learning to classify the morphology of PM2.5 seasonal cycles in East Asia. Machine learning is able to objectively classify the seasonal cycles and, without a priori assumption, is able to clearly distinguish between urban and rural areas. We show an example of this in the Sichuan Basin of China. Furthermore, machine learning is also able to provide physical insights by identifying the key factors associated with each distinct shape of the seasonal cycle, such as highlighting the key role played by the topography and the built environment.