A Numerical Simulation Study On Hydraulic Fracturing Of Horizontal Fractures

Hydraulic fracturing is one of the most important technologies for increasing production in oil and gas industries. Horizontal fracture or vertical fracture may develop. Horizontal fracture is the most common fracture configuration during hydraulic fracture treatments in reservoirs at shallow depth. Most studies of vertical well are focused on the vertical fractures. However studies on horizontal fracture are seldom found in the literature. Horizontal fracture is studied by the Finite Element Method in this thesis. The presence conditions of horizontal fractures are conducted theoretically. The propagation process of horizontal fractures are simulated by the Finite Element Method using the commercial FEM code ABAQUS and some important conclusions are obtained. The implement of horizontal fracture and corresponding control technique can refer to these conclusions.First in this thesis, the hydraulic fracturing technology is introduced in the view of engineering and mechanics. The control equations of this physic process and traditional solution are presented. The history of the theory models for hydraulic fracturing and the present research development are briefly reviewed. Then the hydraulic fracturing is analyzed using Finite Element Method and the control equations of the nonlinear fliud-solid coupling problem are derived. The discrete form of the equations that can be used in programming is brought out and the corresponding solution strategy is discussed.The analytical solution of the stress distribution on wall of non-perforated and single perforated well is conducted. For the complex situation of helical perforated well, the formation fracture initiation pressure is studied by the numerical method. The hydraulic fracturing process of the horizontal fracture is simulated by the commercial FEM code ABAQUS and user self-developed subroutines. The fluid-solid coupling elements are used to describe the mechanical behavior of rock while cohesive elements are employed to simulate the process of fracture initiation and propagation in the formation. The results obtained from numerical simulation are compared with the field measurement data for a fractured oil well with horizontal fracture. Based on the simulation of the selected oil well, the influences of different parameters on horizontal fracture propagation are analyzed. The layer by layer fracturing process of an oil well is simulated either. The simulation of preceding fractures closes on the proppant is implemented by the user self-developed subroutines. The results obtained from the numerical simulation are compared with the field measurement data. Based on the simulation of the layer by ayer fracturing process of a selected oil well, the fracturing processes under different fracture spacings are simulated. The interference among horizontal multi-fractures are studied from the fracture geometry, pressure and the post-fracture flow rate. The propagations of horizontal fractures under helical perforated conditions are studied by numerical and experimental methods. Fracture geometry and treatment pressure are obtained.Several conclusions are drawn from the simulation results.1. The analytical solution of the stress distribution on wall of non-perforated and perforated well is conducted. The occurrence conditions of horizontal fractures are given. The conclusions can be used in engineering to predict the fracture geometry mode. For the conditions of helical perforation that analytical solution can not be obtained, the formation fracture initiation pressure is calculated by the numerical method FEA. The influences of helical perforation parameters on fracture initiation pressure are analyzed and the optimization method is given.2. The hydraulic fracturing process of an oil well in a reservoir is simulated. Based on the consistency between numerical simulation and field measurement data, the influences of different parameters on horizontal fracture propagation are analyzed. The design and implement of horizontal fracture can refer to these conclusions.3. The layer by layer fracturing process of poor and thin formations is studied. Using the user self-developed subroutines, the preceding hydraulic fractures supported by the proppant is modeled and the change of original in-situ stress and pore pressure by the preceding fractures are considered. The results obtained from numerical simulation is consistent well with field measurement results, based on which the interference among horizontal multi-fractures are studied from the fracture geometry, pressure and the post-fracture flow rate. The influences of different fracture spacings on horizontal multi-fractures interference are obtained. The concept of effective fracturing spacing is proposed.4. The horizontal fractures geometry and propagation pressure under different helical perforation parameters are obtained by numerical and physical methods. The optimization for parameters of helical perforation is given. This thesis presents a comprehensive study on the hydraulic fracturing of horizontal fractures. And the conclusions supply the mechanism of hydraulic fracture of horizontal fractures.