A New Method for Determination of Reservoir Pressure

Abstract

Abstract This paper presents a simple and practical technique for determination of reservoir pressure from pressure buildup tests. The technique is based on the wellbore pressure solutions to an instantaneous source, including wellbore storage (afterflow) effects. The new technique is applicable to different flow regimes, such as cylindrically and spherically radial. The technique is sufficiently general that it may be applied to a wide variety of well/test configurations such as DST and wireline formation tester as well as vertical and horizontal wells. The new technique is compared with the well-known Horner method. If the flow rate is well stabilized and the producing time is sufficiently long before the buildup test, the technique gives the same results as the Horner method. However, the new technique works better than the Horner method if the producing time is short, the flow rate is unstable and/or flow regimes are not fully developed. Well tests in low-permeability (tight) or low-pressure reservoirs are well suited for this new technique because frequently they do not flow to the surface or sustain the flow rate long enough so that the conventional interpretation methods can be used. The technique can also be applied readily to wells in unconsolidated formations that produce sand, which usually plugs the wellbore during flow periods. For these cases, the technique will provide good estimates for permeability, skin, and reservoir pressure. A few buildup test examples are presented for the application of the technique.