Abstract: This paper presents two methods for easy determination of water influx in reservoirs based on the material balancetheory of reservoirs, i.e., the Net Production Volume Curve, and the Production Index Curve. These methods can be used for esti-mation of water influx in reservoirs without any assumption of aquifer shape and size by applying the production performancedata. Hence the tedium of the conventional trial-and-eror calculations and obvious uncertainty could be overcome in applicationof the easy and practical new methods.

Key words: reservoir, edge water, bottom water, water influx, mat erial balance method