Browsing by Subject "Hydrocarbon reservoirs--Simulation methods"
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Item Iteratively coupled reservoir simulation for multiphase flow in porous media(2008-05) Lu, Bo, 1979-; Wheeler, Mary F. (Mary Fanett)Fully implicit and IMPES are two primary reservoir simulation schemes that are currently used widely. However, neither of them is sufficiently accurate or ef- ficient, given the increasing size and degree of complexity of highly heterogeneous reservoirs. In this dissertation, an iterative coupling approach is proposed and developed to solve multiphase flow problems targeting the efficient, robust and accurate simulation of the hydrocarbon recovery process. In the iterative coupling approach, the pressure equation is solved implicitly, followed by the saturation equation, which is solved semi-implicitly. These two stages are iteratively coupled at the end of each time step by evaluating material balance, both locally and globally, to check the convergence of each iteration. Additional iterations are conducted, if necessary; otherwise the simulation proceeds to the next time step. Several numerical techniques are incorporated to speed up the program convergence and cut down the number of iterations per time step, thus greatly improving iterative model performance. The iterative air-water model, the oil-water model, and the black oil model are all developed in this work. Several numerical examples have been tested using the iterative approach, the fully implicit method, and the IMPES method. Results show that with the iterative method, about 20%-40% of simulation time is saved when compared to the fully implicit method with similar accuracy. As compared to the IMPES method, the iterative method shows better stability, allowing larger time steps in simulation. The iterative method also produces better mass balance than IMPES over the same time. The iterative method is developed for parallel implementation, and several test cases have been run on parallel clusters with large numbers of processors. Good parallel scalability enables the iterative method to solve large problems with millions of elements and highly heterogeneous reservoir properties. Linear solvers take the greatest portion of CPU time in reservoir simulations. This dissertation investigates advanced linear solvers for high performance computers (HPC) for reservoir simulation. Their performance is compared and discussed.Item Nitrogen injection into naturally fractured reservoirs(2007-05) Vicencio, Omar Alan, 1966-; Sepehrnoori, Kamy, 1951-Naturally fractured reservoirs are complex and constitute a large amount of the world’s oil reserves. Their complexity usually is represented by numerical models based on conceptual abstractions. When most recoverable oil is present in low-permeability rocks, the dual porosity model appears to be the most efficient approach for simulating naturally fractured reservoirs. The rhythms of exploitation in a fractured reservoir can cause field pressure to decline drastically and be reflected in the reduction of oil production rates and the formation of a secondary gas cap. Therefore, field pressure maintenance using gas injection can be an attractive method from technical and economical points of view. A similar approach has been implemented in Cantarell field, the largest oil field in Mexico, characterized as a dual porosity system with a black oil fluid. The simulation of the largest nitrogen injection project in the world for a giant naturally fractured reservoir was carried out to perform a detailed study of the nitrogen injection by using a conceptual model. The objectives of this research are 1) Study the impact of nitrogen injection on oil recovery and nitrogen distribution by injecting nitrogen through different scenarios, and using simplified models with homogeneous and heterogeneous properties; 2) Study the injection of different gases at the same reservoir conditions; 3) Determine the variations of temperature that mainly occur in the gas cap and oil zone using a thermal compositional case study; 4) Study the impact of nitrogen distribution by injection at surface and elevated temperatures; 5) Study the nitrogen injection based on uncertain properties that impact the nitrogen distribution and the oil recovery under the gravity drainage mechanism; 6) Investigate the effects of matrix subgridding in vertical and horizontal directions on total oil production by using a stacked conceptual model; and 7) Develop an analytical model that describes the advancement of the nitrogen front through a fracture system for a gas-oil phase equilibrium system under reservoir pressure maintenance. Since the data used for this research is based on black oil fluid characterization and the fractures are responsible for fluid transport, our starting point was the construction of a single porosity case study using a black oil formulation considering only the fracture pore volume. Subsequently, we increased complexity of the modeling to determine the variations of temperature in the reservoir and to investigate the impact of nitrogen distribution by injecting nitrogen at standard and elevated temperatures. Finally, we developed a simple analytical model that describes the movement of nitrogen injected front by using basic equations for fluid-flow in permeable media such as the Buckley Leveret theory. The development of the analytical model will help reservoir engineers to better understand the problem of gravity drainage in fractured carbonate reservoirs and also to grasp the dynamics of fluid-flow in naturally fractured reservoirs.Item Nitrogen injection into naturally fractured reservoirs(2007) Vicencio, Omar Alan; Sepehrnoori, KamyNaturally fractured reservoirs are complex and constitute a large amount of the world’s oil reserves. Their complexity usually is represented by numerical models based on conceptual abstractions. When most recoverable oil is present in low-permeability rocks, the dual porosity model appears to be the most efficient approach for simulating naturally fractured reservoirs. The rhythms of exploitation in a fractured reservoir can cause field pressure to decline drastically and be reflected in the reduction of oil production rates and the formation of a secondary gas cap. Therefore, field pressure maintenance using gas injection can be an attractive method from technical and economical points of view. A similar approach has been implemented in Cantarell field, the largest oil field in Mexico, characterized as a dual porosity system with a black oil fluid. The simulation of the largest nitrogen injection project in the world for a giant naturally fractured reservoir was carried out to perform a detailed study of the nitrogen injection by using a conceptual model. The objectives of this research are 1) Study the impact of nitrogen injection on oil recovery and nitrogen distribution by injecting nitrogen through different scenarios, and using simplified models with homogeneous and heterogeneous properties; 2) Study the injection of different gases at the same reservoir conditions; 3) Determine the variations of temperature that mainly occur in the gas cap and oil zone using a thermal compositional case study; 4) Study the impact of nitrogen distribution by injection at surface and elevated temperatures; 5) Study the nitrogen injection based on uncertain properties that impact the nitrogen distribution and the oil recovery under the gravity drainage mechanism; 6) Investigate the effects of matrix subgridding in vertical and horizontal directions on total oil production by using a stacked conceptual model; and 7) Develop an analytical model that describes the advancement of the nitrogen front through a fracture system for a gas-oil phase equilibrium system under reservoir pressure maintenance. Since the data used for this research is based on black oil fluid characterization and the fractures are responsible for fluid transport, our starting point was the construction of a single porosity case study using a black oil formulation considering only the fracture pore volume. Subsequently, we increased complexity of the modeling to determine the variations of temperature in the reservoir and to investigate the impact of nitrogen distribution by injecting nitrogen at standard and elevated temperatures. Finally, we developed a simple analytical model that describes the movement of nitrogen injected front by using basic equations for fluid-flow in permeable media such as the Buckley Leveret theory. The development of the analytical model will help reservoir engineers to better understand the problem of gravity drainage in fractured carbonate reservoirs and also to grasp the dynamics of fluid-flow in naturally fractured reservoirs.