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Numerical Simulation of Fluid Flow in Fracture-Cave System Dominated Carbonate Reservoirs: Taking Akekule Nosing Structure (North Tarim Basin, China) for Example


Tahe oilfield, lying in Akekule nosing structure of North Tarim Basin, is the most prolific oilfield demonstrated in the marine formations in China. The reservoir spaces are mainly independent dissolved cave systems in the Ordovician carbonate formations. Although the hydrocarbon development has been proceeded for almost two decades of years there, it is still an open question about the control and distribution of the oil and gas accumulations. In this research, the model of episodic flow induced by cyclic stress is proposed as the mechanics of oil and gas migrating in the fracture-cave systems. In the model, the fracture networks form the channels for flow, and the fluid pressure in caves caused by the stress on the cave walls provides the driving force. This conceptual model is applied to Akekule nosing structure by numerical simulation. The methods for determination of fracture density and flow velocity are reviewed, and the related constitutive equations are introduced. The geological model is critical for simulation of stress field so that the divided elements and the set of elastic moduli should be able to reflect the heterogeneity of the modeled geologic body. A method of quais-3D geological model is developed to simulate the structure configuration underground. The simulation results about flow velocity have supplied significant information on the flow trend in different tectonic stages. Combining with the locations of hydrocarbon sources, the oil and gas charge history and the total charge amount, a general pattern is advanced about multi-stage oil and gas charge and distribution in the Ordovician of Akekule nosing structure.