Preservation conditions for marine shale gas at the southeastern margin of the Sichuan Basin and their controlling factors

Hu, Dongfeng; Zhang, Hanrong; Ni, Kai; Yu, Gaoming

doi:10.1016/j.ngib.2014.11.009

Cited by 37 publications

(22 citation statements)

References 4 publications

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“…It is recognized that shale gas is composed of adsorbed gas, free gas, and a small amount of dissolved gas 14 . The strong tectonic destruction of the Sichuan Basin reveals that shale gas desorption is one of the key factors controlling the successful exploration and development of shale gas in the Sichuan Basin 15,16 . However, knowledge of the shale gas desorption is lacking, as it is mostly based on physical simulation experiments 17,18 .…”

Section: Introductionmentioning

confidence: 99%

Characteristics, capability, and origin of shale gas desorption of the Longmaxi Formation in the southeastern Sichuan Basin, China

Tang

Jiang

et al. 2019

Sci Rep

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Shale gas desorption and loss is a serious and common phenomenon in the Sichuan Basin. The characteristics, capability, and origin of shale gas desorption are significant for understanding the shale gas reservoir accumulation mechanism and guiding shale gas exploration. The shale gas of the Longmaxi Formation in the southeastern Sichuan Basin was studied based on a shale gas desorption simulation experiment, combined with mineral composition, total organic carbon, specific surface area, isothermal adsorption, and scanning electron microscope (SEM) data. Here, the shale gas desorption capability was quantitatively evaluated, and its controlling factors are discussed. The results show that the shale gas desorption process within the Longmaxi Formation varies significantly. The total time of the desorption process varies from 600 min to 4400 min, and it mainly occurs by the 98 °C desorption stage. The desorption capability of the lower Formation is markedly weaker than that of the upper Formation, and it is mainly determined by the shale properties. Organic matter (OM) is the most important controlling factor. As the OM content increases, the specific surface area, methane adsorption capacity, and OM pores increase, leading to a rapid decrease in shale gas desorption capability. In addition, feldspar exhibits a positive correlation with shale gas desorption capability due to its large pores but low specific surface area.

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Section: Introductionmentioning

confidence: 99%

Characteristics, capability, and origin of shale gas desorption of the Longmaxi Formation in the southeastern Sichuan Basin, China

Tang

Jiang

et al. 2019

Sci Rep

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“…In both exploration and production of shale gas, brittleness and ductility of shale are important evaluation parameters as they are closely related to natural shale fracture (Ding et al 2012), artificial hydraulic fracturing , drilling (Eshkalak et al 2015;Zeng et al 2015), permeability (Ghanizadeh et al 2013) and gas preservation (Yarali and Kahraman 2011;Gale et al 2014;Hu et al 2015;Liu and Sun 2015;Zeng et al 2015). Brittleness is one of the most important mechanical parameters of unconventional gas shale reservoir estimation when it comes to hydraulic fracturing (Gasparrini et al 2014;Holt et al 2015) and borehole wall stability assessment and gas preservation risk (Ingram and Urai 1999;Hu et al 2014;Zhou et al 2014). Brittle shales are more likely to be naturally fractured and will also be more likely to respond well to hydraulic fracturing treatments (Nobakht et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production

et al. 2017

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Brittleness and ductility of shale are closely related to shale gas exploration and production. How to predict brittleness and ductility of shale is one of the key issues in the study of shale gas preservation and hydraulic fracturing treatments. The magnitude of shale brittleness was often determined by brittle mineral content (for example, quartz and feldspars) in shale gas exploration. However, the shale brittleness is also controlled by burial depth. Shale brittle/ductile properties such as brittle, semibrittle and ductile can mutually transform with burial depth variation. We established a work flow of determining the burial depth interval of brittle-ductile transition zone for a given shale. Two boundaries were employed to divide the burial depth interval of shale brittle/ductile properties. One is the bottom boundary of the brittle zone (BZ), and the other is the top boundary of the ductile zone (DZ). The brittle-ductile transition zone (BDTZ) is between them. The bottom boundary of BZ was determined by the overconsolidation ratio (OCR) threshold value combined with pre-consolidation stress which the shale experienced over geological time. The top boundary of DZ was determined based on the critical confining pressure of brittle-ductile transition. The OCR threshold value and the critical confining pressure were obtained from uniaxial strain and triaxial compression tests. The BZ, DZ and BDTZ of the Lower Silurian Longmaxi shale in some representative shale gas exploration wells in eastern Sichuan and western Hubei areas were determined according to the above work flow. The results show that the BZ varies with the maximum burial depth and the DZ varies with the density of the overlying rocks except for the critical confining pressure. Moreover, the BDTZ determined by the above work flow is probably the best burial depth interval for marine shale gas exploration and production in Southern China. Shale located in the BDTZ is semi-brittle and is not prone to be severely naturally fractured but likely to respond well to hydraulic fracturing. The depth interval of BDTZ determined by our work flow could be a valuable parameter of shale gas estimation in geology and engineering.

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“… 23 Furthermore, previous studies that have investigated the preservation conditions regarding faults, uplift, tectonic styles, and sealing capacity of the roof and floor have concluded that good preservation conditions are key factors and prerequisites for shale gas enrichment. 24 , 25 A rigid framework, pressure shadow, and overpressure play crucial roles in preserving pores, 23 , 26 , 27 implying that changes in minerals and pressure in shales affect the preservation condition. Because the Qiongzhusi Formation shale was formed early and experienced complex diagenesis during burial, the minerals and pores in the shale are strongly modified.…”

Section: Introductionmentioning

confidence: 99%

Impact of Minerals and Sealing Systems on the Pore Characteristics of the Qiongzhusi Formation Shale in the Southern Sichuan Basin

Liu

Zhou

et al. 2022

ACS Omega

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The characteristics, distribution, and preservation of pores are vital in controlling the storage and distribution of shale gas. The Qiongzhusi Formation shales taken from different members with similar tectonic and thermal evolutions were used to evaluate the response of pore characteristics to minerals and sealing systems using field-emission scanning electron microscopy and gas adsorption. Because of differences in mineral structure and arrangement, feldspar, organic matter (OM)–clay, OM–rutile, and OM–apatite aggregates facilitate multiple types of pores in the shale and influence the relative proportions of surface porosity for different types of pores owing to differences in mineral structure and arrangement. Rigid frameworks and pressure shadows formed by rigid minerals and OM–mineral aggregates preserved OM and pores to some extent. The sealing capacity of the floor controls the sealing system and hydrocarbon expulsion efficiency of the Qiongzhusi Formation in different members. During thermal evolution, the amount of hydrocarbons generated and expelled affected the stress equilibrium state between the pore pressure and external stress, influencing the compaction intensity of shales. The OM pore development characteristics were evolved with variation in the stress equilibrium state in different sealing systems. Once the stress equilibrium state was disrupted, the OM pores deformed, narrowed, or even closed under the influence of compaction owing to the loss of overpressure support. The pore characteristics of the Qiongzhusi Formation shales responded significantly to different sealing systems. A few OM pores are flat and slitlike in the open system, whereas numerous OM pores are round and elliptical in the semiopen system. Meanwhile, the average diameter of the OM pores in the open system was reduced by approximately 40.2% compared with that of the semiopen system. Furthermore, the pore volume and specific surface area of the mesopores for open system shales were reduced by 38.4% and 37.7%, respectively, compared to the semiopen system. These findings will improve the understanding of the distribution and preservation of pore in shale and help assess the sweet-spot members for the Qiongzhusi Formation shale gas.

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Preservation conditions for marine shale gas at the southeastern margin of the Sichuan Basin and their controlling factors

Cited by 37 publications

References 4 publications

Characteristics, capability, and origin of shale gas desorption of the Longmaxi Formation in the southeastern Sichuan Basin, China

Characteristics, capability, and origin of shale gas desorption of the Longmaxi Formation in the southeastern Sichuan Basin, China

Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production

Impact of Minerals and Sealing Systems on the Pore Characteristics of the Qiongzhusi Formation Shale in the Southern Sichuan Basin

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