A Novel Dynamic Model to Simulate Waterflood Induced Fractures in Low Permeability Reservoirs

Abstract

In China, a number of low permeability reservoirs have few fractures at the first stage of development, such as Ansai Oilfield in Changqing and Xinmin Oilfield in Jilin. However, they show fracture influenced characteristics gradually with the processing of waterflood later on. It could be attributed to the waterflood induced dynamic fractures generated during the waterflood process. The presence of the dynamic fractures could lead to volcanic water flooding and directly impact the effectiveness of reservoir development. Based on abundant field data and laboratory data, a new dynamic model to simulate waterflood induced fractures in low permeability reservoirs is established. Compared with the existing models of dynamic fracture, this new model describes the dynamic variation of morphology and permeability of the fractures changing with the formation pressure simultaneously. Thus, this model gives higher reservoir simulation accuracy. In this thesis, the influences of dynamic fractures on water cut of production well, the water injection timing and the water injection pressure are discussed respectively. Simulation results show that dynamic fractures significantly influence the development effects of low permeability reservoirs. This model can predict the development results of low permeability reservoirs with dynamic fractures. It gives guidance to adjust the strategy of injection wells and production wells in time. Thus, oil recovery and economic benefits could be increased.

Influence of Mineral Composition on Initiation Pressure of Waterflood-Induced Fractures in Tight Sandstone Reservoir

“…By evaluating the strength factor at the fracture tips, the dynamic characterization of fractures can help determine the static fracture conditions (static, closed, or extended) at different time steps. − The second model uses the increment of fracture length to present and simulate the extension process of WIFs for simplification. During the fracture initiation simulation, the current formation pressure of blocks needs to be evaluated if it reaches the critical pressure with the preassumed fracture extension direction, and the evolution process of WIFs is simulated by establishing the equations for dynamic change of fracture permeability with both increasing and decreasing formation pressure. − The third model divides the simulation area into homogeneous reservoir and fracture equivalent areas. This homogeneous reservoir is a low permeability formation with constant permeability, and the conventional oil–water relative permeability curve is applied for the porous flow.…”

An Improved Embedded Discrete Fracture Model with Fracture Growth for Water-Induced Fracture Simulation in Low Permeability Reservoirs

“…In recent years, the discrete fracture model (DFM) was used to realize the dynamic changes of fractures [14,15] but was limited to the complexity of grid division. A dynamic fracture model framework was established in which the opening and closure of fractures were reflected by permeability change of grids [16,17]; however, the model oversimplifies the characterization of fractures. So far, analytical fracture models coupling with traditional reservoir numerical simulator were used to simulate water-induced fractures by most scholars; some innovative solutions such as dynamic DFM and dynamic fracture model were proposed in recent years, but shortcomings exist when dealing with fracture propagation.…”