Predicting Gas Well Performance Coning Water in Bottom-Water-Drive Reservoirs

Abstract

ABSTRACT Depletion strategy of a gas reservoir underlain by an active water drive requires careful thought and planning. Producing rate and completion interval are the apparent key considerations in a depletion scheme because of the potential water coning that may affect the ultimate recovery. As this study indicates, both the considerations are relatively unimportant from the stand point of theoretical ultimate recovery. The primary purposes of this investigation are to develop an analytical solution for the water coning problem and to provide guidelines on the depletion strategy in thin reservoirs (< 60 ft). A systematic study of the variables indicates that permeability and pay thickness are the most important variables governing coning phenomenon. Other variables such as penetration ratio, horizontal to vertical permeability ratio, well spacing, producing rate, and the impermeable shale barriers have very little influence on both the water-gas ratio response and the ultimate recovery. Generalized analytical solutions that are developed in graphical form, using a numerical coning simulator, allow a multitude of calculations. These calculations include predicting a well's behavior with or without a production history, determining an economical withdrawal rate, generating a rate-time profile, and estimating a breakthrough time. The type curves could also be used as a diagnostic tool to identify possible completion problems.