Analysis of Capillary Pressure Effects on Well Tests in Solution Gas-drive Reservoirs.

摘要

The effect of capillary pressure on well test is investigated. Solution gas-drive, homogeneous and naturally fractured reservoirs are considered. A numerical simulator, with a Warren and Root formulation for the case of fractured reservoirs, is used to generate synthetic data. For homogeneous reservoirs the procedures of Perrine-Martin and pseudo-pressure are evaluated under the presence of capillary pressure. As expected the influence of capillary pressure is more pronounced in buildup tests than in drawdown tests. A capillary pressure number is proposed to evaluate the importance of capillary forces over viscous forces in different regions in the reservoir. For naturally fractured reservoirs, the effects of including capillary pressure in the fracture and matrix systems are investigated. It is observed that, under certain conditions, both drawdown and buildup tests show capillary pressure effects in different flow periods under transient conditions. Also, the influence of capillary pressure on the flow transfer between matrix and fracture is documented, observing that the oil flow rate per unit volume from the matrix to the fracture system is lower when capillary pressure is taken into account.