Researches on calculation methods of aquifer influx for gas reservoirs with aquifer support

Abstract

Abstract The existence of aquifers in gas reservoirs has important influences on the development of gas wells. Water will invade into gas reservoirs when formation pressure decreases during the production of a gas well and then change the well production characteristics severely. It is very important to research the aquifer invasion mechanisms and evaluate the aquifer influx for good knowing and exploring the gas reservoir. In this paper, we have conducted three methods to research the aquifer influx characteristics by evaluating the value of aquifer influx and aquifer influx rate that vary with the production time. Three methods are the Blasingame method, the FMB (Flowing Material Balance) method and the MBE (Material Balance Equation) method. Based on the Blasingame conventional type-curves, the normalized well production data of a gas well influenced by aquifers can be divided into three influx periods: no-aquifer, early-aquifer and middle-late-aquifer influx period. The no-aquifer influx period production data are used to determine well initial gas in place and as a base, and the early-aquifer influx period production data are used to obtain aquifer influx and aquifer influx rate quantitatively. The novel three methods presented can elucidate the aquifer influx characteristics clearly and determine aquifer influx rate quantitatively just using well dynamic production data based on the Fetkovich model. Meanwhile, a simple numerical simulation model was built to verify the three methods, which shows that these three methods are reliable and really have strong practicability in developing gas field reservoirs with aquifer support.