New approaches for analyzing transient pressure from oil and water two-phase flowing reservoir

Theory and practice in the past on well testing reservoir with multi-phase flow such as oil and water system achieved limited success. Methods include multi-phase pseudo-pressure, pressure squared and total compressibility, total mobility, i.e. Perrine-Martin (P-M) method. As recognized by the industry, multi-phase pseudo-pressure approach was flawed, while only P-M method is applicable in strictly oil-water system. Multi-phase flow well testing research subject attracted the oil industry's interest again is purely due to the onset of permanent down hole gauge (PDG), which made long term multi-phase flow transient pressure data at every stage available. This paper explored in depth the problem of well testing in oil-water two-phase flowing system further. Four types of flow mechanisms were modeled and studies were conducted through numerical well testing. These are: (1) dispersed flow with uniform saturation; (2) dispersed flow with non-uniform saturation; (3) oil-water segregated flow and (4) oil reservoir with aquifer-support. Case (1) is an ideal case, where oil and water assumed to be fully dispersed across the entire reservoir thickness. But in practice, water saturation is non-uniform in reservoir, so it is in fact the case (2). Case (3), segregated flow occurs when gravity forces are dominating, leading to complete segregation of oil overlying water. Such situation can also be due to early water breakthrough in layered reservoir with high permeability formation. Case (4) characterizes the situation where the well is completed in part of the formation away from the water formation in order to prevent water coning. This will create a different flow problem due to spherical flow. Transient data were generated through numerical experiments for every defined flow mechanisms above. Considering relative permeability curves, traditional P-M method was fully examined and modified to obtain the true reservoir properties such as absolute permeability in these situations. Following the numerical well testing procedures, interpretation issues due to the difference between the theory and practice were addressed much more properly and clear. Copyright 2009, Society of Petroleum Engineers.