| Description |
Fluid production from tight and shale gas formations has increased significantly, and this unconventional portfolio of low-permeability reservoirs accounts for more than half of the gas produced in the United States. Stimulation and hydraulic fracturing are critical in making these systems productive, and hence it is important to understand the mechanics of the reservoir. When modeling fractured reservoirs using discrete-fracture network representation, the geomechanical effects are expected to have a significant impact on important reservoir characteristics. It has become more accepted that fracture growth, particularly in naturally fractured reservoirs with extremely low permeability, cannot be reliably represented by conventional planar representations. Characterizing the evolution of multiple, nonplanar, interconnected and possibly nonvertical hydraulic fractures requires hydraulic and mechanical characterization of the matrix, as well as existing latent or healed fracture networks. To solve these challenging problems, a reservoir simulator (Advanced Reactive Transport Simulator (ARTS)) capable of performing unconventional reservoir simulation is developed in this research work. A geomechanical model has been incorporated into the simulation framework with various coupling schemes and this model is used to understand the geomechanical effects in unconventional oil and gas recovery. This development allows ARTS to accept geomechanical information from external geomechanical simulators (soft coupling) or the solution of the geomechanical coupled problem (hard coupling). An iterative solution method of the flow and geomechanical equations has been used in implementing the hard coupling scheme. The hard coupling schemes were verified using one-dimensional and two-dimensional analytical solutions. The new reservoir simulator is applied to learn the influence of geomechanical impact on unconventional oil and gas production in a number of practical recovery scenarios. A commercial simulator called 3DEC was the geomechanical simulator used in soft coupling. In a naturally fractured reservoir, considering geomechanics may lead to an increase or decrease in production depending on the relationship between the reservoir petrophysical properties and mechanics. Combining geomechanics and flow in multiphase flow settings showed that production decrease could be caused by a combination of fracture contraction and water blockage. The concept of geomechanical coupling was illustrated with a complex naturally fractured system containing 44 fractures. Development of the generalized framework, being able to study multiphase flow reservoir processes with coupled geomechanics, and understanding of complex phenomena such as water blocks are the major outcomes from this research. These new tools will help in creating strategies for efficient and sustainable production of fluids from unconventional resources. |
