Comparative study of shale parallel/vertical laminar shear fracture inflow characteristics
In shale gas extraction,shear fractures in the reservoir serve as critical seepage channels and show different inflow characteristics depending on the direction of shale stratification.To investigate the influence of laminations on the conductive properties of shale shear fractures,shear fractures with parallel and perpendicular laminations were created in the Longmaxi Formation shale in the Fuling area of Chongqing,China.The surface of the fractures was characterized using a three-dimensional morphology scanner to analyze their initial morphology and mechanical openness.Gas conduction experiments were conducted under different effective stresses using a three-axis rheological experimental system to analyze the conductive properties of the fractures.The results show that vertical shear fractures have a rougher surface,a larger standard deviation of the opening distribution,and more small opening fractures(＜200 μm).When the effective stress is lower(＜8 MPa),the equivalent hydraulic openings of vertical shear fractures(17-100 μm)are higher than those of parallel shear fractures(22-66 μm),indicating that vertical shear fractures have a stronger flow-conducting ability.As the effective stress increases,parallel shear fractures exhibit higher flow-conducting ability than vertical shear fractures.The parallel shear fracture also demonstrates stronger flow conductivity with increasing effective stress.The critical Reynolds number of the vertical shear fracture(3.1-15.6)is larger than that of the parallel shear fracture(4.2-8.5),making it less likely to occur under the same conditions of nonlinear flow.Gas flow analysis reveals that vertical shear fractures exhibit laminar,transitional,and turbulent flows,while parallel shear fractures only exhibit transitional and turbulent flows.
rock mechanicsshale laminaeshear fracturesfracture openinginfusion abilitygas flow patter
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