| A comprehensive review on the state of the art in the hydraulic fracturing technology is presented. Though in the last decades, substantial effort has been devoted to develop effective hydraulic fracturing technology, there are still many problems remain. Since the hydraulic fracturing process is very complicated, there is tremendous challenge in modeling hydraulic fracturing process, and any analytic solution is impossible. In this thesis, the finite element method is adopted to model the hydraulic fracturing process. The mechanism of fracture initiation and propagation can be explained, and the fracture geometry can be predicted by numerical simulating of hydraulic fracturing with the finite element method, which is of great value in theory and application.Damage mechanics theory is adopted to study the mechanism of fracture initiation and propagation. During the injection of fracturing fluid, part of the fracturing fluid permeates into the formation, the other remains in the fractures. The two parts of the fracturing fluid together increase the effective stress at the fracture tip. Once the effective stress at the fracture tip reachs the corresponding tensile strength, as the further increasement of damage, the value of the effective stress that the fracture tip can hold decreases as the opening displacement increases, until compete damage occurs.From the equilibrium equations of the solid skeleton and continuity equations of fluid for saturated porous media, a mathematical model of reservoirs is constructed. In the model, Jaumann stress rate formula is introduced to address the finite deformation effect of the solid skeleton of porous media. The parameters including the in-situ stress, initial pore pressure, initial fluid density and initial porosity of a reservoir layer are also taken into account in the model. With finite element discretization in the space domain and implicit differential discretization in the time domain, an instantaneous nonlinear fluid-solid coupling incremental finite element formula is derived based on the weighted residual formula for the equivalent equations of the mathematical model. The degrees of freedom of the finite element formula include nodal displacements and nodal pore pressures. This model gains its generality due to few simplification hypothesis and comprehensive factors being taken into account.An axisymmetric model is contructed by the FEA software ABAQUS, numerical simulation study is carried out on four oil wells in Daqing Oilfield with the model. Among the four oil wells, one is staged fractured, and the others are limited entry fractured. The model consists of perforation, wellbore, cement casing, oil layer, micro-annulus and transverse fracture. The effect of volume fraction of sand on the properties of fracturing fluid is modeled with the user subroutine UFIELD of ABAQUS. The numerical simulations yield the results including stress, strain, displacement, pore pressure, fracture geometry, and history curves of pressure at the facture mouth.For staged fracturing, since the number of perforations is large, the perforation friction is negligible, and the pressure at the fracture mouth equals to bottomhole pressure. The pressures at bottomhole and on surface for staged fracturing can be directly measured in filed treatment. The pressure curve at the fracture mouth putputed from numerical simulation fits well with corresponding field data, which validates the model. In this paper, the drag ratio formula is adopted to calculate the pipe string friction by combining field treatment curves and correcting corresponding coefficient of drag ratio formula. From the obtained data of the pipe string friction, a formula calculating the pipe string friction by inverse seeking the parameters in the drag ratio formula is proposed. There is a good coincidence between simulated pressure at the fracture mouth and field measured bottomhole pressure, which verifies the correctness of the proposed formula of pipe string friction. For limited entry fracturing, the perforation friction is significant. A calculation formula for perforation friction based on the calculation methods of discharge coefficient and perforation diameter is derived. In limited entry fracturing, only the surface pressure can be obtained from field measured data, the surface pressure can be got from simulation results. The agreement of surface pressures from field treatment and numerical simulation validates the calculation formula of the proposed discharge coefficient and perforation diameter.By adjusting the parameters in the aforementioned model, a parametric study is carried out to ascertain the effect of the parameters. The parameters includes the rock permeability, the elastic modulus, the fracture energy, the magnitude and direction of in-situ stress as well as the viscosity coefficient of fracturing fluid. The mechanism of parameters effect on simulation results is presented.Furthermore three-dimensional finite element numerical simulation technology is carried out for simulating the staged fracturing process of an oil well in Daqing Oilfield with FEA software ABAQUS. The proposed numerical model includes perforation, wellbore, cement casing, oil layer, barrier layer, micro-annulus and transverse fracture. Micro-annulus fracture and transverse fracture generate simultaneously and a typical T-shaped fracture occurs at the early stage of treatment history, then the micro-annulus disappears and only the transverse fracture remains and propagates. The simulation results are in good coincidence with field measurement data.The effect of geographic and petrophysical parameters of oil and barrier layers under the layered geographic condition on the fracture geometry (especially the fracture height), bottomhole pressure and pore pressure of the formation is studied. These parameters include the in-situ stress, elastic moduli and tensile strengths in barrier layer, and the viscosity of the fracturing fluid. The mechanism of the effect of these parameters on simulation results is analyzed.
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