A Well Test Model for Composite Reservoir with Resistance Force on Interface

ABSTRACT

Tazhong No.1 gas field is a typical vug-fractured carbonate gas condensate reservoir with the characteristics of high heterogeneity and complex geological and dynamics. A physical and effective hole-diameter mathematical model for well test in the composite reservoir is established, which considers the resistance force on interface. Specifically, the following factors are involved, including wellbore storage and skin factor of inner boundary, fracture open of interface, and infinite boundary of outer boundary. Moreover, the exact solution of wellbore pressure is obtained in terms of ordinary Bessel functions in the Laplace space. The numerical computation of the solution is obtained by using the Stehfest numerical inversion method, and the behavior of the system is studied as a function of various interface parameters. Results show that the composite radius controls the time of the interface performance. The larger the composite radius, the later the interface performance begins. In addition, the condition of open fracture has a heavy impact on the transitional zone performance. Resistance force on the interface disguises the influence of the condition of the open fracture, which is more apparent with larger resistance force. Comparisons with the regular well test model shows that the new model can improve the data utilization, reduce multiple solutions of well test analysis and increase the accuracy on the identification of formation parameters and evaluation stimulation. The method is useful for the reservoir dynamic description.

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