ABSTRACT:

The commingling production is widely used in Coal Measure Shale Reservoir (CMSR) to reduce the drilling cost and increase production efficiency. The mechanics characteristics of different rocks play an important role during the exploitation of coal measure shale reservoir. Therefore, it is necessary to investigate the mechanical properties and in-situ stresses situation of CMSR. In this paper, the mechanical parameters, deformation characteristics and in-situ stress tests in coal measure shale reservoir are studied, thus the vertical difference of different rock, including coal, shale, mudstone, limestone could be obtained. The results show that the heterogeneity between layers of coal measure shale reservoirs is strong and the characteristics of natural fractures are significantly different. Coal and shale show obvious plastic characteristics under high uniaxial pressure and high confining pressure, and the plastic characteristics of rocks increase with the increase of confining pressure, and the increase range of plastic characteristics of different rocks also has obvious difference. The tensile strength and fracture toughness of different rocks vary greatly, the tensile strength of mudstone is up to 11.456 MPa and the lowest tensile strength of coal is 0.296 MPa. The in-situ stress distribution of different layers on the vertical of the reservoir is obtained. which indicates that the maximum horizontal in-situ stress difference between layers reaches 7 MPa. The results give a deep understanding of the longitudinal variation characteristics of such complex coal series shale layered reservoir.

1. Introduction

With the improvement of oil and gas reservoir exploitation technology and the increase of oil and gas resource demand, unconventional oil and gas resources are increasingly attracting attention, and gradually become an important strategic resource and powerful supplement, among which coal measure shale gas is one of the important types of unconventional natural gas (Zou et al, 2018). Coal measure shale reservoirs in China is rich in shale gas and coal-bed methane, which have high content of coal, shale, mudstone and limestone rocks, reservoir stratification, small single layer thickness, the cumulative thickness is big, staggered superimposed, vertically into continuously, the gas bearing alternate development, the development difficulty is high, the engineering general selecting a layer by means of the fracture on the vertical communication more set of comprehensive development of coal reservoir of coalbed methane and shale gas (Hou et al, 2019; Zhang et al, 2020).

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