Abstract
Jointed rocks are typical examples of heterogeneous materials with joints. The existence of joints influences the physical properties of rock mass and propagation of fractures, which can affect production operations in engineering. A series of simulations is performed to understand the failure patterns and fracture propagation behavior of jointed rocks in hydraulic fracturing. Three points, that is, dip‐angle joint, joint strength, and complex joints, are considered in the simulations. Results demonstrate three basic kinds of hydraulic fractures on jointed rock, namely, along the joint, across the joint, and partly along the joint and partly across the joint. The maximum principal stress is the control factor of fracture propagation in global scale, and the joint plane is the control factor of fracture propagation in local scale. In the propagation path, when the dip angle is small or the joint is weak, the fracture propagates along the joint; otherwise, the fracture propagates across the joint. In the multijoint interconnection models, hydraulic fractures propagate along joints in the tensile stress regions near the propagating fracture tip without dip angle limitation. Subsequently, the fractures connect with one another to form a complex fracture network based on the joint morphology.
Highlights
Joint is a structural plane of discontinuities formed by sedimentation
To understand the hydraulic fracture propagation behavior of the joint strength specimens, a dip angle of 60° is considered on the basis of the first group simulation, that is, the hydraulic fracture propagation of the 60° dip model is simultaneously controlled by the joint plane and the maximum principal stress
Given the weak cementation effect and small fracture toughness of the joint material, some secondary fractures propagate along the joint planes when the main fracture propagates. is finding suggests that hydraulic fracture propagation is controlled by the joint plane in local scale
Summary
Joint is a structural plane of discontinuities formed by sedimentation. Jointed rock masses are commonly encountered in civil, mining, and petroleum engineering because they are universally distributed over the earth’s surface. As a control factor of rock mass stability [1], joints influence rock failure patterns and fracture propagation behavior. Hydraulic fracturing was used for jointed rock masses of sandstones, mudstones, shales, and coal seams to form complex fracture networks and improve the permeability of unconventional reservoirs [3,4,5]. Extensive experimental and numerical studies on the actual kinematics of hydraulic fracture propagation of jointed rocks were performed by researchers all over the world [6,7,8,9,10,11,12]. A study on the mechanical influence of joints and the growth process of hydraulic fractures of jointed rocks is essential, and it is even helpful in determining efficient fracturing scenarios or production designs in field operations. Failure Process Analysis (RFPA)2D2.0-Flow. e RFPA is a code to simulate fracture propagation following the continuum damage principle [13, 14] of heterogeneous rock materials. e RFPA has been used extensively, and the creditability of its simulations has been proven many times since its development [15,16,17,18,19,20,21,22,23]
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