Comparative analysis and practical application of abnormal pressure gas reservoir models using a mature abnormal gas reservoir

In the early portion of production from a gas reservoir, reliable knowledge of initial gas-in-place is vital for any gas field development from the economical and technical point of view. On dealing with abnormally high pressure gas reservoirs, two distinct slopes are observed when p/z vs. cumulative gas production is plotted as a preliminary tool to predict reserves. In this case, the second slope is steeper than the first one, but usually the gas-in-place is estimated based on the early behavior. Unfortunately, an accurate estimate of GIIP will be only determined after observing the second slope due to production. To overcome this difficulty, several material balance models have been proposed to calculate the GIIP in abnormally pressured gas reservoirs using only the early production data. In this article, these proposed models and their applications are briefly, but mathematically reviewed. Moreover, the production, pressure and reservoir data of an Iranian abnormally high pressure gas reservoir are used to investigate these existing models for this case study. The point in our published data is that the production data is from both the first (abnormal) and the late (normal) portion of the gas reservoir life, hence, the actual GIIP can be correctly estimated. To be more exact, a range for this actual GIIP is defined to make sure that this estimated actual GIIP is the true GIIP, as the reference value for evaluation. Therefore, the advantages and disadvantages of the suggested models, their compatibility and predictability can be validated with available data from this mature abnormal gas reservoir. (orig.)