Abstract

Naturally fractured reservoirs (NFRs) always have flow networks that are more or less irregular, discontinuous, or clustered. NFR with such spatially non-uniform distribution of fractures is called partially naturally fractured reservoir (PNFR). An improved understanding of pressure response is required to characterize PNFR. This paper presents a better understanding of well test pressure response of PNFR.

Stochastic modeling was used to generate various geological models with different fracture intensities. Single phase liquid flow through stochastically generated reservoirs is simulated by a numerical reservoir simulator. Dual-porosity / dual-permeability model was selected to simulate PNFR. A vast database of pressure transient responses of the reservoirs with varying fracture intensity, matrix permeability and fracture porosity is presented in this paper. Pressure derivative was used to analyze the pressure transient responses.

Pressure derivative analysis indicates multiple V-shapes representing various sets of fracture intensities. It is observed that with the increase of fracture porosity V-shape become more pronounced. It is also observed that with the increase of matrix permeability, the duration of composit radial flow is prolonged. The shapes of pressure drawdown plots indicate the level of fracture connectivity of the reservoir. Whereas the fracture connectivity is related to the fracture intensity (FI). The critical value of fracture intensity is observed around 60 percent which results in the formation of connected fracture network.

The interpretation of pressure responses of PNFR becomes very difficult and challenging because the available simplified models do not relate to reality of reservoirs. This paper quantifies the fracture intensity for a broad range of PNFR with the use of pressure transient responses. This quantification is a major contribution to the present literature.

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