Hydraulic Fracture Nonplanar Propagation Mechanism In Multi-Layered Reservoir

There are a lot of challenges in scheme design for reservoir stimulation in multilayered reservoir for last several decades because it is difficult to understand the law of fracture propagation,especially in multi-layers combined with shale gas,tight gas and coal bed gas.The vertical propagation range of the hydraulic fracture is one of the important consideration in multi-layered fracturing design,which affects the efficiency of the hydraulic fracturing and is the key of the success in fracturing operation.It is difficult to understand the fracture propagation law in composite reservoir,which brings great challenges in making scheme for reservoir stimulation.Thus,a prediction of the fracturing vertical propagation range and whether the fracturing will penetrate the cover is necessary to determine property fracturing parameters.Based on These questions,the main contents are as follows:1 Experimental Investigation on Hydraulic Fracture Propagation in Mixed Layers.The natural outcrop rocks from the eastern margin of Ordos Basin are selected and mixed in a certain way to carry out the physical simulation experiments with true tri-axial fracture system.The effects of differential stress,differential elastic modulus and cleats on the hydraulic fracture initiation and propagation are studied.The result shows that the stress condition and location of fracture initiation commonly control the propagation direction of hydraulic fracture.2 Propose a viable method on hydraulic fracturing simulation based on discontinuum mechanicsApplied the discrete element method to the study the hydraulic fracture propagation mechanism.Tri-axial experiments are simulated to verify the reliability of mechanics and to calibrate the mechanical parameter,while a steady seepage test is simulated to verify the reliability of fluid flow algorithm and to calibrate permeability.3 Simulation of hydraulic fracture propagation using discrete element method in multilayered reservoir.Based on discontinuum mechanics,a discrete element method is employed for numerical simulation to analyze the effect of some critical parameters on multi-layers fracturing.The result shows,in most cases,that the stress condition and natural weak plane of interface control the propagation direction of hydraulic fracture.The increasing displacement and fluid viscosity would compensate the influence of the interface.