Development of linear-element boundary element method for inverse solution from induced far-field displacements to reservoir loading source

Abstract

An inverse solution strategy using linear element of Boundary Element Method(BEM)was developed, which will become a novel application base to potentially reflect the equivalent mechanical effect around reservoir corresponding to CO2 spreading during its injection process. Firstly, a linear-element BEM code was studied to improve the accuracy in analyzing the connection between induced ground minute deformations and underground inner loading. Secondly, the space regularization was adopted to deal with the ill-posed problem during the optimization to inverse problem solution. The boundary conditions of a near-field structure as active source were reversely figured out in an efficient numerical way based on its passive deformation that was sampled at a few specific positions at far field. Meanwhile, the effectiveness of linear-element BEM in solving inverse problems was demonstrated. Finally, based on the implementation of hydraulic fracturing in a coal seam in Alberta, Canada, the monitored data of its induced surface displacements was input to invert the equivalent internal pressure onto are-opened fracture within reservoir. The results show that the proposed inverse solution workflow and programmed algorithm are applicable to effectively guiding hydraulic fracturing interpretation so as to further facilitating coal bed methane recovery.