Poroelastic solution of a wellbore in a swelling rock with non-hydrostatic stress field  

作　　者：Mohsen S.Masoudian Zhongwei Chen Christopher Leonardi 

机构地区：[1]Beck Engineering Pty.Ltd.,Chatswood,New South Wales,2067,Australia [2]School of Mechanical and Mining Engineering,The University of Queensland,St.Lucia,Queensland,4072,Australia

出　　处：《Journal of Rock Mechanics and Geotechnical Engineering》2022年第2期303-314,共12页岩石力学与岩土工程学报（英文版）

基　　金：supported by the Advance Queensland Industry Research Fellowship (mid-career) scheme;the University of Queensland (UQ),and the proponents of the UQ Centre for Natural Gas (Australia Pacific LNG, Santos, and Arrow Energy)。

摘　　要：The stress distribution around a circular borehole has been studied extensively. The existing analytical poroelastic solutions, however, often neglect the complex interactions between the solid and fluid that can significantly affect the stress solution. This is important in unconventional gas reservoirs such as coalbeds and shale formations. In order to address this limitation, this paper presents the development of a poroelastic solution that takes into account the effect of gas sorption-induced strain. The solution considers drainage of the reservoir fluid through a vertical wellbore in an isotropic, homogenous,poroelastic rock with non-hydrostatic in situ stress field. The sorption-induced shrinkage of coal is modelled using a Langmuir-type curve which relates the volumetric change to the gas pressure. The redistributed stress field around the wellbore after depletion is found by applying Biot’s definition of effective stress and Airey’s stress functions, which leads to a solution of the inhomogeneous Biharmonic equation. Two sets of boundary conditions were considered in order to simulate the unsupported cavity(open-hole) and supported cavity(lined-hole) cases. The implementation was verified against a numerical solution for both open-hole and lined-hole cases. A comparative study was then conducted to show the significance of the sorption-induced shrinkage in the stress distribution. Finally, a parametric study analysed the sensitivity of the solution to different poroelastic parameters. The results demonstrate that the developed solution is a useful tool that can be employed alongside complex flow models in order to conduct efficient, field-scale coupled hydro-mechanical simulations, especially when the stressdependent permeability of the reservoir is of concern.

关 键 词：Poroelasticity Coupled geomechanics Analytical solution Wellbore Cavity expansion Coalbed methane(CBM) 

分 类 号：TU45[建筑科学—岩土工程]