Modifying rock compressibility to analyze the production data of non-volumetric gas and gas condensate reservoirs

Abstract

Production data analysis, particularly the flowing material balance method, has been used for many years as an efficient, practical, and significant method to obtain important reservoir parameters. Many studies have been done to develop the flowing material balance method in different types of reservoirs which in most of them, the main limitation is that the reservoir has been considered to be volumetric. Therefore, despite being widely used, this method has not been well developed for non-volumetric water drive reservoirs. In the present work, an extremely simple yet very accurate method was introduced to obtain an excellent estimation of average pressure and gas in place of non-volumetric dry gas and gas condensate reservoirs. In our proposed method, a modified rock compressibility parameter was presented to modify current flowing material balance equations which have been developed for volumetric dry gas and gas condensate reservoirs previously. Using the proposed compressibility, the modified flowing material balance equations can be used for non-volumetric dry gas and gas condensate reservoirs producing with constant bottomhole pressure during the boundary-dominated flow period. Moreover, the iterative procedures to estimate average pressure and gas in place of these kinds of reservoirs were presented in detailed steps. Also, the validity of the proposed flowing material balance equations was performed using a commercial numerical reservoir simulator. The obtained results prove the efficiency of the proposed method. Furthermore, due to the high amount of uncertainty in aquifer parameters, an uncertainty analysis has been performed on aquifer parameters using Monte-Carlo simulation. The results of the study indicated that the determination of appropriate aquifer parameters has a significant impact on the estimation of reservoir parameters which can be obtained using a combination of uncertainty analysis and the proposed flowing material balance technique.