Permeability evolution of the lamina induced fractures (LFs) during the triaxial compression rupture phase

Abstract

Laminated sandstone is abundant in tight reservoirs filled with the hydrocarbon fluid that flows through the lamina induced fractures (LFs). To study the fracture permeability evolution during the rupture phase in the triaxial compression process of laminated sandstone, we tested 12 column samples with different lamina angles in a particular experimental apparatus during the triaxial compression process. This study proposed a permeability model for the lamina induced fractures, which is composed of a variable of radius strain and three critical parameters, including the lamina angle, the initial rupture radius strain, and the rupture stress difference. The model was built based on the Palmer and Mansoori's fracture permeability model (the P-M model), the modified Tien and Kuo's LF failure criteria (the T-K criteria), and the redefined rock compressibility (the change rate of porosity with the radius strain). In this research, the simulation agreed well with the test results. The permeability evolution lines were characterized by two phases: a rapidly increase phase and a following stable phase. The samples with the medium lamina angles were usually characterized by a more rapidly increasing phase and a higher stable fracture permeability, indicating a preferential hydraulic fracturing target for the tight oil exploration. Furthermore, to satisfy the flow principle of the lamina induced fractures, it is proposed that horizontal wells of the laminated tight sandstone reservoir should be designed in a polyline or oblique trajectory which should be intersected with the formation lamina to create a proper perforating direction.