Analysis of Pressure Buildup Tests in Naturally Fractured Reservoirs: Field Cases

Abstract

ABSTRACT Field cases of pressure build-up tests are presented for two reservoirs which showed existence of fractures on cores. The nature of the pressure build-up data on these tests have shown the importance of preparing various cross-plots to diagnose the existence of fractures in the reservoir. In many cases presented, 2 parallel straight lines with transition in between were noticed on Horner plot. In some cases, the pressure build-up tests conducted in the early life of the well were typical of a homogeneous system with afterflow and skin, although linearity of data points was obvious on Δ p vs square root of shut-in time plot. Subsequent pressure build-up tests of the well, however, showed 2 parallel lines with transition in between on Horner plot. The tests with 2 parallel slopes, showed unique trend on Pollard plot since it yielded two intersecting straight lines after early period, not reported earlier. The storativity ratios are estimated to be rather high in spite of the large matrix block height estimated, perhaps due to high matrix permeability. These facts underscores the importance of using all available evidences to derive physically consistent parameters for analysis of naturally fractured reservoirs.