Time Lapse Pressure Transient Analysis ForWells Near Edge Water Drive

Abstract Uncertainties of aquifer size/strength in a field simulation study often results in a poor match for prediction of water breakthrough at wells which in field context can lead to irreversible loss of production and lack of preparation time for associated field planning. Additionally, the pressure transient analysis (PTA) data can be interpreted inaccurately before and after the water breakthrough at wells. It is known that time-lapse PTA can be used for estimation of reservoir flow capacity and detection of fluid contact movements. This paper deals with investigations of extended PTA through numerical models under a range of mobility ratio conditions to reduce uncertainties in the estimation of well production rates, proximity of a fluid contact to well, and accurate reservoir characterization in edge water drive (EWD) systems. Several local-grid-refinement schemes are tested and optimized for run time and improved accuracy. Time-steps are selected to enable understanding of pressure transient data for varying mobility ratio scenarios. Time-lapse pressure build-up, well bottom-hole pressure, average reservoir pressure and reservoir-aquifer boundary pressure are studied for each mobility ratio case. A synthetic data set was employed for time-lapse PTA and including the log-derivative response for each mobility ratio and water cut. The transient pressure is analyzed for its unique characteristics and behavior. Time-lapse PTA response for wells in EWD systems is discussed in detail. There is an indication of productivity loss and increase in skin after water breakthrough and is also observed in log-log derivative response. A practitioner may inadvertently select false infinite-acting radial flow line for PTA analysis after water breakthrough leading to pessimistic estimates of formation capacity and productivity. All the build-ups after water breakthrough show changes of slope in the middle-time region which provides an indication of productivity loss due to edge aquifer. A typical dip in middle time region of derivative curves is also observed at high water cuts greater than 25%. A new dimensionless breakthrough time (tDBT) is introduced in this paper. This is found to be useful concept in understanding breakthrough behavior under non-unit mobility ratio conditions relative to unit mobility ratio. The unit mobility ratio at breakthrough and pressure transient behavior can be computed with high precision both analytically and numerically. The study presents new results of the time lapse pressure transient behavior for varying mobility nature at different water cut levels at a well near an edge water contact.