Factors influencing microstructure and porosity in shales of the Wufeng-Longmaxi formations in northwestern Guizhou, China

Cao, Taotao; Xu, Hao; Liu, Guangxiang; Deng, Mo; Cao, Qi; Yao, Yiyu

doi:10.1016/j.petrol.2020.107181

Cited by 35 publications

(20 citation statements)

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“…Sichuan Basin is currently a primary target area for shale gas exploration in China, with the lower Paleozoic Silurian Longmaxi Formation marine shale as the principal target strata. − The Longmaxi Formation in southeastern Sichuan Basin, China, possesses such natural advantages for shale gas development as wide distribution area, great effective thickness, and moderate burial depth. , Unlike conventional gas reservoirs, shale gas has the characteristics of “in situ accumulation”. Typically, shale gas is distributed in nanoscale pores and adsorbed on the surfaces of organic matter and mineral particles using “free state”, “adsorbed state”, and “dissolved state”. − Among them, contents of free gas and adsorbed gas are dominant, which are major types of shale gas exploitation at this stage. , Regardless of the form of shale gas, organic matter and inorganic minerals are hosting carriers of gas, which directly controls the development of reservoir spaces and the gas content of shale. , The mineral composition of shale is complicated, typically composed of quartz, clay minerals, feldspar, and calcite with a certain amount of pyrite.…”

Section: Introductionmentioning

confidence: 99%

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Qin

et al. 2021

Energy Fuels

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Influences of the characteristics of organic matters and mineral compositions on the development of shale microscopic pores were discussed through performing low-temperature nitrogen adsorption, whole-rock "X" diffraction, and field emission scanning electron microscope on black organic-rich shale samples of Longmaxi Formation in the Dingshan area, southeastern Sichuan Basin, in combination with the characteristics of shale organic matters. The shale in the Dingshan area has complex mineral composition, which is mainly quartz and clay minerals. Both contents range from 23% to 72% and 36% to 70%, respectively. The vertical variation is obvious, and there are few feldspar and carbonate rocks; the pyrite content is more than 2%. The bottom shale has high brittleness and gradually decreases in the vertical direction. The brittleness index is between 0.481 and 0.627 and is concentrated above 0.5. It shows strong compressibility and is easy to form a complex network system in hydraulic fracturing. Quartz and feldspar mainly provide secondary dissolved pores, intercrystalline mineral pores, and nanoedge gaps in contact with organic matter. They have no obvious correlation with the specific surface area of shale but have a weak correlation with pore volume. They mainly control the development of macropores. Organic matter develops many hydrocarbon-generating pores, which strongly correlate with the specific surface area and a weak correlation with pore volume. It mainly controls the development of micromesopores. Clay minerals mainly provide a large number of interlaminar pores and interlayer fractures in the clay. The intergranular pores of clay and clay have a weak correlation with pore volume and specific surfaces. They contribute to the development of shale micropores, mesopores, and macropores. Pyrite mainly provides intercrystalline pores and mold pores. By restricting the interaction with organic matter, the development of shale pores is promoted within a certain content range. When the content exceeds this range, the development of micropores is inhibited. The conversion threshold in the Dingshan area is 5.0%.

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Section: Introductionmentioning

confidence: 99%

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Qin

et al. 2021

Energy Fuels

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“…However, after applying the kerogen corrections, the corrected porosity ranging from 5 to 10% gives more accurate results that can be well-compared with core porosity (Table 2 and Figure 7). Moreover, the clay minerals also affect the pore structure of shale that directly affects the water saturation [37,38]. The Goldwyer shale also consists interparticle pores influenced by illite that may change the water saturation (Figure 6).…”

Section: Resultsmentioning

confidence: 99%

Porosity and Water Saturation Estimation for Shale Reservoirs: An Example from Goldwyer Formation Shale, Canning Basin, Western Australia

Iqbal

Rezaee

2020

Energies

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Porosity and water saturation are the most critical and fundamental parameters for accurate estimation of gas content in the shale reservoirs. However, their determination is very challenging due to the direct influence of kerogen and clay content on the logging tools. The porosity and water saturation over or underestimate the reserves if the corrections for kerogen and clay content are not applied. Moreover, it is very difficult to determine the formation water resistivity (Rw) and Archie parameters for shale reservoirs. In this study, the current equations for porosity and water saturation are modified based on kerogen and clay content calibrations. The porosity in shale is composed of kerogen and matrix porosities. The kerogen response for the density porosity log is calibrated based on core-based derived kerogen volume. The kerogen porosity is computed by a mass-balance relation between the original total organic carbon (TOCo) and kerogen maturity derived by the percentage of convertible organic carbon (Cc) and the transformation ratio (TR). Whereas, the water saturation is determined by applying kerogen and shale volume corrections on the Rt. The modified Archie equation is derived to compute the water saturation of the shale reservoir. This equation is independent of Rw and Archie parameters. The introduced porosity and water saturation equations are successfully applied for the Ordovician Goldwyer formation shale from Canning Basin, Western Australia. The results indicate that based on the proposed equations, the total porosity ranges from 5% to 10% and the water saturation ranges from 35% to 80%. Whereas, the porosity and water saturation were overestimated by the conventional equations. The results were well-correlated with the core-based porosity and water saturation. Moreover, it is also revealed that the porosity and water saturation of Goldwyer Formation shale are subjected to the specific rock type with heterogeneity in total organic carbon total clay contents. The introduced porosity and water saturation can be helpful for accurate reserve estimations for shale reservoirs.

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“…Zhang et al explored the influences of shale maturity on porosity and considered the effects of investigating organic and inorganic porosities by NMR . On the basis of microstructure features, Cao et al analyzed the factors influencing porosity in shale at the Wufeng–Longmaxi Formation in Guizhou . Krzyżak et al related the low-field NMR approach to quantitatively and precisely determine the movable porosity .…”

Section: Introductionmentioning

confidence: 99%

Estimation of Porosity in Gas Shale Using ¹H NMR Measurement: Implications for Enhanced Shale Gas Recovery

Yang

et al. 2021

Energy Fuels

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The identification of shale porosity is of fundamental significance for evaluating reservoir quality in gas-shale plays, where the various methods rarely discern the adsorbed porosity and free porosity. Comprehensive measuring campaigns, as well as reliable isothermal adsorption data sets, show that the adsorbed porosity and free porosity can be validly identified by using 1 H NMR (nuclear magnetic resonance) and isothermal adsorption experiments. Here, we show that the T 2 distribution of individual T 2 peaks in "CH 4 -saturated shale", adsorbed film density, and Boyle's law can be applied to calculate the adsorbed porosity, free porosity, and total porosity. We estimated the adsorbed porosity and found that NMR measurements have remarkable capacity dynamics for characterizing CH 4 saturation in shale samples. Furthermore, the adsorbed film density can be optimized by isothermal adsorption data. The novel method established in this paper directly computes the adsorption film density according to the physical characteristics of the measured isotherm adsorption. The purpose of this investigation is to unravel some of the mysteries surrounding the assessment of the adsorbed and free porosities of unconventional hydrocarbon development. The integrated analysis of these measurements helps us to better understand the adsorbed porosity, free porosity, and total porosity of samples from conventional and unconventional shale plays.

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Factors influencing microstructure and porosity in shales of the Wufeng-Longmaxi formations in northwestern Guizhou, China

Cited by 35 publications

References 74 publications

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Porosity and Water Saturation Estimation for Shale Reservoirs: An Example from Goldwyer Formation Shale, Canning Basin, Western Australia

Estimation of Porosity in Gas Shale Using ¹H NMR Measurement: Implications for Enhanced Shale Gas Recovery

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Factors influencing microstructure and porosity in shales of the Wufeng-Longmaxi formations in northwestern Guizhou, China

Cited by 35 publications

References 74 publications

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Influence of Mineral Compositions on Shale Pore Development of Longmaxi Formation in the Dingshan Area, Southeastern Sichuan Basin, China

Porosity and Water Saturation Estimation for Shale Reservoirs: An Example from Goldwyer Formation Shale, Canning Basin, Western Australia

Estimation of Porosity in Gas Shale Using 1H NMR Measurement: Implications for Enhanced Shale Gas Recovery

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Estimation of Porosity in Gas Shale Using ¹H NMR Measurement: Implications for Enhanced Shale Gas Recovery