Brittleness evaluation of Wufeng and Longmaxi Formation high-quality shale reservoir in southeast of Chongqing

Liu, Yisheng; Zhu, Zhengping; Pan, Renfang; Hei-Zhi, Wu; Jin, Jineng

doi:10.1007/s12665-022-10274-3

Cited by 4 publications

(1 citation statement)

References 5 publications

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“…Among them, the clay minerals are mainly illite and illite/smectite mixed beds, with an average interbed ratio of 25%. The rocks of the Shahejie Formation are hard and brittle mudstones with a high content of brittle minerals. − For this hard brittle mudstone, it is easy to produce microfractures under a high external force environment. At the same time, the mineral composition and content of interbedded sand and mud are analyzed.…”

Section: Methodsmentioning

confidence: 99%

Study on the Mechanical Properties and Failure Law of Rocks with Interbedded Sand and Mud

et al. 2022

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In view of the borehole instability during the drilling process of the thin sand and mud interbedded sections in the Shahejie Formation, the physicochemical and mechanical properties of sand and mud interbed rock were studied through a series of laboratory tests to determine the main factors influencing the formation instability. The effects of fracture development of interbed sand and mud, mechanical weak plane, borehole trajectory, and seepage effect on borehole stability were evaluated and analyzed through the established model. The results indicated that the microcracks are developed on the lithologic interface due to the change of lithology of the sand–mud interbed. The anisotropy of the mechanical properties of the rocks with interbedded sand and mud is obvious, which leads to the great mechanical weak plane effect on the wellbore stability. The bottom-hole pressure difference leads to the seepage effect, which reduces the effective supporting force of the drilling fluid on the borehole wall and promotes rock sliding and failure along the lithologic interface developed by the sand–mud thin interbedded layer. Considering the influence of the borehole trajectory, mechanical weak plane, and seepage effect, the recommended drilling fluid density in the deviated section is 1.69 g/cm3. The wellbore stability is the best when drilling along the direction of the minimum horizontal principal stress in the horizontal section. Further strengthening the plugging performance of the drilling fluid, drilling through the microfractures vertically on the interbedded lithologic interface, and reducing the lateral vibration of the drilling tools as far as possible are necessary. The research results provide a theoretical basis for the safe drilling of thin sand and mud interbedded strata.

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Section: Methodsmentioning

confidence: 99%

Study on the Mechanical Properties and Failure Law of Rocks with Interbedded Sand and Mud

et al. 2022

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Mechanical behavior and constitutive model of shale under real-time high temperature and high stress conditions

Guo

Cai

et al. 2022

J Petrol Explor Prod Technol

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The high temperature and high in-situ stress geological environment can significantly affect the mechanical properties, failure modes, and deformation characteristics of deep shale reservoirs. In this study, real-time high temperature triaxial compressive tests simulating the deep shale formation environment (temperature: 25–150 °C, confining pressure: 0–100 MPa) are carried out. The GSI-strength degradation and constitutive models are derived based on the Hoek–Brown criterion. The results show that in low confining pressure conditions, the mechanical behavior of shale is greatly influenced by temperature. Compared with shale at 25 °C, the compressive strength of shale at 150 °C decreases by up to 13.7%, and the elastic modulus decreases by up to 36.9%. The peak strain was increased by a factor of up to 1.4, and the yield stress level was advanced by as much as 7.4%. However, in high confining pressure conditions, the shale plasticity characteristics are significantly enhanced and the failure mode is relatively single. The GSI-strength degradation model can well characterize the variation law of shale strength with confining pressure under high temperature conditions. The statistical damage constitutive model matches the actual stress–strain curve very well, and it can fully reflect the deformation and failure characteristics of deep shale. The findings of this study can help us better understand the variation of mechanical properties of deep shale.

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Quantitative characterization of the brittleness of deep shales by integrating mineral content, elastic parameters, in situ stress conditions and logging analysis

Luo,

Wang,

Chen

et al. 2024

Int J Coal Sci Technol

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Deep shale reservoirs (3500–4500 m) exhibit significantly different stress states than moderately deep shale reservoirs (2000–3500 m). As a result, the brittleness response mechanisms of deep shales are also different. It is urgent to investigate methods to evaluate the brittleness of deep shales to meet the increasingly urgent needs of deep shale gas development. In this paper, the quotient of Young’s modulus divided by Poisson’s ratio based on triaxial compression tests under in situ stress conditions is taken as SSBV (Static Standard Brittleness Value). A new and pragmatic technique is developed to determine the static brittleness index that considers elastic parameters, the mineral content, and the in situ stress conditions (BIEMS). The coefficient of determination between BIEMS and SSBV reaches 0.555 for experimental data and 0.805 for field data. This coefficient is higher than that of other brittleness indices when compared to SSBV. BIEMS can offer detailed insights into shale brittleness under various conditions, including different mineral compositions, depths, and stress states. This technique can provide a solid data-based foundation for the selection of ‘sweet spots’ for single-well engineering and the comparison of the brittleness of shale gas production layers in different areas.

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Brittleness evaluation of Wufeng and Longmaxi Formation high-quality shale reservoir in southeast of Chongqing

Cited by 4 publications

References 5 publications

Study on the Mechanical Properties and Failure Law of Rocks with Interbedded Sand and Mud

Study on the Mechanical Properties and Failure Law of Rocks with Interbedded Sand and Mud

Mechanical behavior and constitutive model of shale under real-time high temperature and high stress conditions

Quantitative characterization of the brittleness of deep shales by integrating mineral content, elastic parameters, in situ stress conditions and logging analysis

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