古龙页岩力学特征与裂缝扩展机理

doi:10.11743/ogg20230402

Abstract

Abstract:

The Gulong shale oil represents China’s first attempt at large-scale exploration and exploitation of the oil contained in shale sequences without intercalations. Clarifying the rock mechanical characteristics and fracture propagation mechanisms of the Gulong shale is vital for guiding the selection of landing zones and fracturing design and engineering parameter optimization. In this study， the mineral distribution， thin section observation and rock mechanics tests are performed to clarify the Gulong shale as “fine layered” texture in mechanics and reveal the fracture propagation mechanisms under the control of multiple geological and engineering factors. It is shown that the Gulong shale is characterized by high clay mineral content （Avg. 46.6 %）， strong plasticity， a foliation intensity of up to 1 000～3 000 stripes per meter and strong mechanical anisotropy. Unlike the brittle fracturing of conventional shale， the typical rock samples from Gulong exhibit high-frequency fluctuation in mechanical property， with a fluctuation frequency of 3.33 times per cm for a compressive strength greater than 20 MPa. The fracturing process is observed as a steady gradual process with a slow post-peak stress decline， and along a random path in a zigzagged shape. Meanwhile， in the case of high-density foliation fractures， the hydraulic fractures in the Gulong shale are of complex morphology， with their height and length being significantly constrained. The limited vertical and horizontal extension of hydraulic fractures has been a major constraint for the effective stimulation of the Gulong shale oil reservoir. It is thereby suggested that the hydraulic stimulation of the Gulong shale oil reservoir should follow the principle of controlling near-wellbore fracture branching and further extending distal fracture networks， while placing the fracturing treatment under more effective control to suppress the development of near-wellbore fractures and boost the extension of main fractures to sufficiently expand the stimulated reservoir volume.

Key words: mechanical characteristics, elastoplasticity, fracture propagation, heterogeneity, shale oil, Gulong shale, Songliao Basin

CLC Number:

TE122.2

He LIU, Siwei MENG, Suling WANG, Kangxing DONG, Liu YANG, Jiaping TAO, Lihao LIANG. Mechanical characteristics and fracture propagation mechanisms of the Gulong shale[J]. Oil & Gas Geology, 2023, 44(4): 820-828.

Figures/Tables 12

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材料	均质性系数	弹性模量/GPa	抗压强度/MPa	渗透率/μm²
基质	8	18	90	10^-5
层理	8	12	60	10^-4

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Mechanical characteristics and fracture propagation mechanisms of the Gulong shale

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