Abstract
This study presents a pressure transient analysis technique for determining the initial oil-in-place and the ratio of initial gas to oil, within the drainage area of the test well. The method is based on a combination of the material balance equation, the cumulative production history, individual well rate history and PVT data of the reservoir, with limited well test pressure data. The solution method considers the variable rate production history of each of the wells and combines this data with a global pressure data analysis approach as opposed to the usually employed approach of applying each method in isolation, which often produces erroneous results.
The analysis procedure allows every detail of the reservoir development, rate changes at every well from inception, global (reservoir wide) and local (individual well) fluctuations in pressure to be included in the overall results. Local variations in reservoir rock properties at the well locations are also accommodated in the method. By modifying the analysis technique used for solving the linear material balance, a method is derived that allows the simultaneous determination of the original oil-in-place, and the initial ratio of free gas to oil in the reservoir, without the previous knowledge of one or the other from an independent source, a requirement that is often needed for such solution. A Dynamic Material Balance Program (DMBP), a Visual Basic based program, was developed to implement the solution procedure presented in this paper.
