Large-scale Physical Simulation of Hydraulic Fracturing under True-triaxial Conditions and Analysis of Fracture Propagation

Abstract

ABSTRACT In order to study the effect of in-situ stresses and natural fractures in coal seam on fracture initiation, fracture propagation, fracture morphology and fracture width, a large-scale sample made of similar materials with inner artificial fracture was applied to conduct large-scale true triaxial hydraulic fracturing simulation experiment. Initial angle and final angle of fractured sample were measured by protractor. Fracture width in fracturing process was tested by displacement meter timely. The experimental results indicated that fracture initiation, fracture propagation path and fracture morphology are affected greatly by in-situ stresses and natural fractures in coal reservoir, in-situ stresses is the major influencing factor. Initial angle of hydraulic fracture is mainly affected by the angle between perforations and maximum horizontal stress. Natural fracture is an important factor influencing fracture propagation, which results in leak-off of fracturing fluid and formation of fracture network, but hydraulic fractures gradually turn to the direction of perpendicular to minimum horizontal stress. When vertical stress and minimum horizontal stress are constant, fracture width decreases and fracture length increases with the increasing of maximum horizontal stress. The research results are consistent with existing fracturing theory (fracture width reduces with the increasing of horizontal stress difference) and would provide reference for the improvement of hydraulic fracturing technology and theory.