Quantifying the relative contribution and evolution of pore types to shale reservoir space: Constraints from over-mature marine shale in the Sichuan Basin, SW China

Hui, Shasha; Pang, Xiongqi; Chen, Zhuoheng; Hu, Tao; Shi, Kanyuan; Di, Guidong; Li, Min; Mei, Shuxing; Li, Maowen

doi:10.1016/j.jseaes.2023.105625

Cited by 5 publications

(5 citation statements)

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“…The earliest descriptive pore classification scheme for shale reservoirs was proposed by [12]; this shale pore system is divided into three categories: organic matter (OM) pores, intraparticle (IntraP) pores, and interparticle (In-terP) pores. The development degree of OM pores is influenced by the TOC content and OM type; the pores mainly develop in bitumen [53,63]. Therefore, this study mainly observes the development characteristics of OM pores in bitumen.…”

Section: Fe-sem Characteristics Of Shale Reservoirs With Different Bu...mentioning

confidence: 91%

“…The second type of shale gas content measurement is on-site desorption, including atmospheric [48,49] and pressure-holding coring measurement [50]. Because the coring time of shale gas wells is generally long, the level of natural gas loss could be large [51][52][53]. This has led to controversy over the results of atmospheric on-site desorption.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Studies on Pore Structure and the Gas Content Evolution Mechanisms of Shale Gas Reservoirs at Different Burial Depths in the Longmaxi Formation, Southern Sichuan Basin

Fu,

Zhang,

Jiang

et al. 2023

Applied Sciences

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Micro- and nano-scale pores develop in shale reservoirs, and the associated pore structure controls the occurrence state, gas content, seepage capacity, and micro-migration and accumulation mechanisms of shale gas. For this study, we mainly conducted tests, using field emission-scanning electron microscopy, of the isothermal methane adsorption of powder-sized samples under high temperatures (60–130 °C) and pressures (0–45 MPa), along with methane-saturated nuclear magnetic resonance tests of plug-sized samples under different temperatures (60–100 °C) and pressures (0–35 MPa). These samples were from Longmaxi shale cores from strata at different burial depths from the Zhaotong, Weiyuan, and Luzhou areas. As the burial depth increases, organic pores transform from complex networks to relatively isolated and circular pore-like structures, and the proportion of organic matter-hosted pores increases from 25.0% to 61.2%. The pore size is influenced by the pressure difference inside and outside the pores, as well as the surface tension of organic matter in situ. As the burial depth increases to 4200 m, the main peak of the pore size first increases from 5–30 nm to 200–400 nm and then decreases to 50–200 nm. This work establishes an NMR method of saturated methane on plug-sized samples to test the free gas content and develop a prediction model of shale reservoirs at different burial depths. The gas content of a shale reservoir is influenced by both burial depths and pore structure. When the burial depth of the shale gas reservoir is less than 2000 m, inorganic pores and microfractures develop, and the self-sealing ability of the reservoir in terms of retaining shale gas is weak, resulting in low gas content. However, due to the small pore size of organic pores and the low formation temperature, the content of adsorbed gas increases, accounting for up to 60%. As the burial depth increases, the free gas and total gas content increase; at 4500 m, the total gas content of shale reservoirs is 18.9 m3/t, and the proportion of free gas can be as high as 80%. The total gas content predicted by our method is consistent with the results of the pressure-holding coring technique, which is about twice our original understanding of gas content, greatly enhancing our confidence in the possibility of accelerating the exploration and development of deep shale gas.

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Section: Fe-sem Characteristics Of Shale Reservoirs With Different Bu...mentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Experimental Studies on Pore Structure and the Gas Content Evolution Mechanisms of Shale Gas Reservoirs at Different Burial Depths in the Longmaxi Formation, Southern Sichuan Basin

Fu,

Zhang,

Jiang

et al. 2023

Applied Sciences

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“…The mineral composition is also an important factor that influences shale pore development, which significantly affects the porosity and pore structure of shale [44,83]. The pore types of the FF shales are mainly intergranular and intragranular pores associated with mineral particles, and pore development is obviously controlled by mineral composition.…”

Section: Influence Of Mineral Composition On Shale Pore Developmentmentioning

confidence: 99%

“…The pore development of shale is critical for the accumulation of hydrocarbons in shale. Hydrocarbons exist in three main occurrence states, namely free, adsorbed, a dissolved, in nanometer and micrometer scale pores and fractures in shale reservo [2,82,83]. Free hydrocarbons primarily exist in the macropores and fractures of sha which is the most favorable occurrence state for shale oil and gas exploitation.…”

Section: Implications For Shale Oil Exploration and Developmentmentioning

confidence: 99%

Pore Structure and Geochemical Characteristics of Alkaline Lacustrine Shale: The Fengcheng Formation of Mahu Sag, Junggar Basin

Li,

Hu,

Cao

et al. 2023

Minerals

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Shale oil and gas are currently the major fields of unconventional hydrocarbon exploration and development. The Fengcheng Formation (FF) shale in the Mahu Sag of the Junggar Basin is an alkaline lacustrine organic-rich shale with an extremely prospective shale oil potential. However, its strong heterogeneity and complex pore structure greatly influence the development of shale oil. It is significant to investigate the pore and geochemical characteristics of shale reservoirs for shale oil extraction. In this study, the pore structure and geochemical characteristics of FF have been investigated using core analysis, Rock-Eval pyrolysis, X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), mercury injection capillary pressure (MICP), low-temperature gas adsorption (LTGA), and X-ray computed tomography (X-ray CT). The results show that the shale of FF has moderate organic matter abundance, and the kerogen is mainly of Type II, which is now at the peak of oil generation. Shale minerals are mainly composed of carbonate (dolomite and calcite) and siliceous (quartz and feldspar) minerals, with extremely low clay mineral content. The pore types are mainly intergranular pores (inter-P), intragranular pores (intra-P), and microfractures associated with mineral particles. The pore space is contributed predominantly by micropores of 0.5–1.2 nm and mesopores of 10–50 nm, whereas macropores are underdeveloped. The pores are mostly ink bottle- and slit-shaped, and the pore connectivity is relatively poor. The pore development of shale in the FF is influenced by organic matter abundance, thermal maturity, mineral composition, etc. Organic matter content (TOC), thermal maturity (Ro), and carbonate minerals have a positive effect on pore development, and the pore volume (PV) increases with TOC, Ro, and carbonate minerals. While clay minerals show a negative effect, the PV decreases with clay minerals. Additionally, the influence of the clay mineral content on the pore morphology of shale should not be ignored. This study investigates the pore structure and geochemical characteristics of the alkaline lacustrine shale of FF in Mahu Sag, which is significant to deepen the understanding of alkaline lacustrine shale and to improve the production of shale oil.

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“…Using classification schemes such as that previously proposed [10], researchers categorize these pores into interparticle pores, intraparticle pores, and organic matter (OM) pores for indepth analysis. Image analysis effectively utilizes high-resolution SEM images to determine various properties of different pore types, including their number, size, geometric shape, and area [21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Differential Development Mechanisms of Pore Types under the Sequence Stratigraphic Constraints of the Wufeng–Longmaxi Formation Shale from the Upper Yangtze Platform

Wang,

Xi,

Yan

et al. 2023

Processes

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Various types of pores, including organic and inorganic variations, exhibit distinct impacts on the storage capacity of shale gas reservoirs and play a significant role in shale gas occurrence. However, there is a limited number of studies that have quantitatively addressed the developmental characteristics of these diverse pore types and their primary controlling factors. This paper explores the development of inorganic pores, specifically interparticle pores and intraparticle pores, as well as organic matter (OM) pores within the shales of the Wufeng–Longmaxi Formation in the Upper Yangtze region. Parameters such as areal porosity, pore diameter, and pore number based on the FE-SEM and image digitization are discussed. Additionally, the influence of the sedimentary environment on the development of various pore types through integrated wavelet transform techniques and geochemical analysis are analyzed. This analysis reveals the distinctive mechanisms governing the development of pore types under the sequence stratigraphic constraints. The findings reveal that the Wufeng–Longmaxi Formation within the study area can be classified into four systems tracts (transgressive systems tracts TST1 and TST2, and highstand systems tracts HST1 and HST2). Within TST1+HST1, OM pores emerge as the predominant pore type, contributing to over 65% of the porosity. TST2 similarly displays OM pores as the dominant type, comprising over 45% of the total porosity, with an average OM areal porosity of 7.3%, notably lower than that of TST1+HST1 (12.7%). Differences in OM pore development between TST1+HST1 and TST2 shales are attributed to variations in OM abundance and type. In HST2, inorganic pores are the dominant pore type, primarily consisting of interparticle pores associated with clay minerals, contributing to more than 50% of the porosity, while OM pores remain almost undeveloped. The frequent sea level fluctuations during the sequence stratigraphic evolution caused variations in sedimentary environments across different depositional sequences. These differing depositional environments lead to varying OM content and types, mineral genesis, and content, ultimately resulting in disparities in the development of shale pore types within different sequences.

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Quantifying the relative contribution and evolution of pore types to shale reservoir space: Constraints from over-mature marine shale in the Sichuan Basin, SW China

Cited by 5 publications

References 76 publications

Experimental Studies on Pore Structure and the Gas Content Evolution Mechanisms of Shale Gas Reservoirs at Different Burial Depths in the Longmaxi Formation, Southern Sichuan Basin

Experimental Studies on Pore Structure and the Gas Content Evolution Mechanisms of Shale Gas Reservoirs at Different Burial Depths in the Longmaxi Formation, Southern Sichuan Basin

Pore Structure and Geochemical Characteristics of Alkaline Lacustrine Shale: The Fengcheng Formation of Mahu Sag, Junggar Basin

Differential Development Mechanisms of Pore Types under the Sequence Stratigraphic Constraints of the Wufeng–Longmaxi Formation Shale from the Upper Yangtze Platform

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