Study on vertical multifracture propagations in deep shale reservoir with natural fracture network

Abstract

Building a complex fracture network in a deep shale gas reservoir during multicluster hydraulic fracturing is challenging. On the one hand, hydraulic fractures tend to propagate along shale bedding planes, thus leading to a limited hydraulic fracture height; on the other hand, under the effect of high in situ stress and weak plane of fractures, multihydraulic fractures can hardly initiate and propagate uniformly. All of these will jeopardize the performance of hydraulic fracturing. This paper considers the influence of natural fracture network, shale beddings, fracturing-fluid leakage, and high in situ stresses, and builds a numerical model to simulate multifracture propagations along vertical direction during hydraulic fracturing in deep shale reservoirs. The model is developed based on the theory of solid-fluid coupling and finite element method with pore pressure cohesive element technique are used to simulate multicluster fracture initiation and propagation. Moreover, the model is verified by published experiment data, and a good agreement between model and experiment results is observed. The influences of pump rate and fracturing-fluid viscosity on fracture geometry are discussed, and the flow dynamics around each perforation cluster under different perforation parameters are also studied. Finally, suggestions to improve overall outcome of multicluster hydraulic fracturing are also provided.

Multiwell Fracturing Characteristic in Layered Heterogeneous Formation and the Optimization of Stimulated Reservoir Volume

“…With the continuous injection of fracturing fluid, the normal stress keeps growing linearly until it reaches the material tensile strength and then initializes the damage. The initial linear elastic relation can be written as bold-italict = { true t n t s t t } = [ true E n n E n s E n t E n s E s s E s t E n t E s t E t t ] { true ε n ε s ε t } = bold-italicE bold-italicε where E is the stiffness matrix of the cohesive element during elastic response stage.…”