Abstract:

Dynamic reserve evaluation is a critical step for reservoir internal adjustment and potential development. For gas reservoirs with single-well production, the traditional material balance method is commonly used. In this method, dynamic reserves are calculated using the average formation pressure and cumulative gas production obtained by extrapolating single-well pressure buildup curves. However, in multi-well production scenarios, inter-well interference exists, and pressure buildup after shut-in often exhibits an abnormal trend of rising first and then declining, making it difficult to accurately determine the average formation pressure. As a result, dynamic reserves predicted by the material balance method may have significant errors. To more accurately evaluate dynamic reserves under inter-well interference conditions, an inter-well interference coefficient was introduced. By coupling the pseudo-steady-state productivity equation of a single well within a rectangular boundary of constant volume (with evenly distributed wells) with the material balance equation, a new method for calculating dynamic reserves was developed using only single-well flowing bottom-hole pressure, gas production rate, and cumulative gas production. Relationship curves were plotted between the pseudo-pressure difference per unit gas production of a single well and the total material balance time, where the inverse of the curve slope represented the dynamic reserves. Given an initial estimate of dynamic reserves, iterative calculations were performed using the curves, and the resulting reserve value was obtained until the error between the calculated and estimated values was sufficiently small. Case studies demonstrated that under inter-well interference conditions, the new method only required single-well flowing pressure, production rate, and reservoir cumulative gas production, without the need for shut-in pressure measurements, showing stronger applicability than the traditional material balance method. It improved calculation accuracy by 12.6% and better aligned with actual production conditions. Additionally, the new method yielded consistent dynamic reserve values when applied to any two connected wells, enabling the determination of inter-well connectivity. The research findings hold significant practical value for improving dynamic reserve calculation accuracy and assessing well connectivity under inter-well interference conditions.

Key words: inter-well interference, dynamic reserves, pseudo-steady-state productivity equation, material balance method, inter-well connectivity