Organic matter enrichment mechanism of Youganwo Formation oil shale in the Maoming Basin

Zhao, Difei; Guo, Ying-Hai; Wang, Geoff; Zhou, Xueqing; Zhou, Yuanyuan; Zhang, Jiaming; Ren, Guohao

doi:10.1016/j.heliyon.2023.e13173

Cited by 5 publications

(6 citation statements)

References 35 publications

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“…where Sg is the gas saturation, %; Tsc is the ground standard temperature, 298.15 K; Z is the gas compressibility factor; φ is the porosity, %; Psc is the ground standard pressure, 0.101 MPa; ρr is the density of gas-bearing rocks, in g/cm 3 ; T is the formation temperature, K; P is the formation pressure, MPa.…”

Section: Traditional Methodsmentioning

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: Traditional Methodsmentioning

confidence: 99%

“…Due to the rapid growth in energy demand and progress in exploration technologies, shale reservoirs have become a valuable target for the production of natural gas and oil around the world [1][2][3]. The matrix of shale reservoirs is tight, with extremely low porosity and permeability, and a large number of nanopores are developed [4,5].…”

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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“…During the adsorption and desorption processes, temperature, relative pressure range (P/P 0 ), and equilibrium interval are set to 77.35 K, 0.005~1.0 and 30 s, respectively. Quantitative pore volumes were calculated by the Density Functional Theory (DFT) according to Gregg & Sing (1982) [30]. To characterize macropores, solid samples were cut into 1 cm 3 to measure high-pressure mercury intrusion carried on the AutoPore IV 9500 Micrometeric instrument at the China University of Geoscience (Wuhan).…”

Section: Sampling and Methodsmentioning

confidence: 99%

Paleo-Environment Induced Full-Scale Pore Variation in the Low Matured Shale: A Case Study of the Third Member of the Jiufotang Formation at the Lujiapu Rift Basin, Northeast China

Li,

Guo,

Liu

et al. 2023

Minerals

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Shale in the third member of the Jiufotang Formation at the Lujiapu Rift Basin is a new potential target for shale oil exploration and has rarely been studied before. In order to study pore structure and its controlling factors, shale compositions are mainly analyzed by X-ray Diffraction (XRD), and the characterization of full-scale pore structures is studied by the field-emission scanning electron microscope (FE-SEM), low-temperature N2 adsorption, and high-pressure mercury intrusion porosimetry (high-pressure MIP). According to composition and micro-texture, shale samples in the third member of the Jiufotang Formation are classified into three types: laminated organic matter-lean shale (TOC < 2%), unlaminated organic matter-intermediate shale (2% < TOC < 4%) and laminated organic matter-rich shale (TOC > 4%). Most shale samples are dominated by interparticle pores, with many of them filled by diagenetic minerals. All the shale samples are most developed in mesopores, whose development is mainly controlled by quartz content. And macropores with a diameter of 10,000 nm~100,000 nm are the secondary developed pores, which are influenced by both the paleoenvironment and diagenesis (especially clay transformation). Full-scale pore variations in laminated organic matter-lean shale, unlaminated organic matter-intermediate shale, and laminated organic matter-rich shale are ultimately related to their paleoenvironments.

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“…For example, regarded the paleoproductivity of surface water and the relatively stable anoxic environment as the main factors controlling the enrichment of organic matter in the Lucaogou Formation [27]. A case study carried out by Zhao et al (2023) proposed that the relatively high bio-productivity of water and low input of detrital matter were favorable for the preservation of OM [114]. However, these previous studies did not relate the mechanism of organic matter enrichment to cyanobacterial blooms.…”

Section: Mechanism Of Organic Matter Enrichment Under Cyanobacterial ...mentioning

confidence: 99%

Permian Cyanobacterial Blooms Resulted in Enrichment of Organic Matter in the Lucaogou Formation in the Junggar Basin, NW China

et al. 2023

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The Permian Lucaogou Formation in the Junggar Basin, NW China is the target layer for shale oil exploration, but its hydrocarbon precursors have remained the focus of debate. In this study, we investigated the Lucaogou source rocks throughout Well J10025 by conducting detailed petrological, paleontological, and geochemical analyses for the purpose of revealing the occurrence of cyanobacterial blooms as specific hydrocarbon events in the upper Lucaogou Formation. The morphological characteristics of the microfossils and the geochemical signatures of the microfossil-bearing layers support a biological affinity with Microcystis, a kind of cyanobacteria. Microcystis observed as colonial forms embedded in the upper Lucaogou Formation are of great abundance, indicating the presence of cyanobacterial blooms. They were further evidenced by cyanobacteria-derived biomarkers including low terrestrial/aquatic ratio, high 2α-methylhopane index values, and high abundance of 7- and 8-monomethyl heptadecanes. The blooms occurred in a semiarid and brackish paleoenvironment with anoxic to suboxic water conditions and intermittent volcanic eruptions. Permian Microcystis blooms contributed to the enrichment of organic matter in the upper Lucaogou Formation in two main ways: by directly promoting the accumulation of algal biomass and by creating an oxygen-depleted environment for better preservation of organic matter. This study adds a new record to the geological occurrences of cyanobacterial blooms in the Permian, and provides unique insight into the hydrocarbon generation of Jimsar shale oil in the Junggar Basin.

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Organic matter enrichment mechanism of Youganwo Formation oil shale in the Maoming Basin

Cited by 5 publications

References 35 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

Paleo-Environment Induced Full-Scale Pore Variation in the Low Matured Shale: A Case Study of the Third Member of the Jiufotang Formation at the Lujiapu Rift Basin, Northeast China

Permian Cyanobacterial Blooms Resulted in Enrichment of Organic Matter in the Lucaogou Formation in the Junggar Basin, NW China

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