Understanding well performance with surveillance data

Abstract This study presents an inception-to-maturity data acquisition philosophy and deriving value from such surveillance. Specifically, translating wellhead pressures (WHP) to bottomhole pressures (BHP) allowed many reservoir-engineering calculations during the flow period. While conversion of WHP to BHP proved feasible during a flow test, measurements showed that shut-in tests do not lend themselves for such treatment because of rapid heat dissipation of a low-heat-capacity fluid, such as gas. Therefore, we relied upon flow-after-flow (FAF) tests that were embedded in monthly variable-rate production measurements to obtain average reservoir pressure and absolute open-flow potential. These average pressures enriched those that were obtained with downhole gauges from shut-in tests for the material-balance analysis. The resultant time-dependent inflow–performance relationship (IPR) and absolute-open-flow potential helped understand well performance. Indeed, evolution of declining IPR slope led to the identification of gradual wellbore blockage in one of the wells completed openhole. Downhole video recording confirmed mechanical issues in two openhole completions. Production logging showed preferential flow from the upper section of the thick carbonate interval in two wells. However, residual doubts remained about possible flow up the annulus in the openhole/slotted liner completions. Analytic modeling confirmed that the notion of preferential flow up the annulus is untenable.