Analytical Approach to Predict Water Breakthrough Time Using Time-Lapse Pressure Transient Analysis: Application to Single Gas Well Reservoirs

Abstract Water breakthrough time (WBT) prediction is crucial for effective reservoir management with significant impact on field life and recovery. Time-Lapse Pressure Transient Analysis (PTA) can be used as one of the tools to predict WBT based on aquifer boundary movement over time. This paper aims to propose a simple yet effective approach for predicting WBT and cumulative gas production at WBT for gas reservoirs with single producer based on boundary movements observed in consecutive pressure build-ups (BUs). BUs conducted over the span of three years were analyzed using appropriate analytical boundary models for each well. For consecutive BUs, upward shift in derivative during late time region indicated aquifer boundary movement towards the well. For each BU, equivalent radius corresponding to aquifer boundary was calculated based on PTA boundary distances. Correlation between equivalent radii and cumulative gas production was then established. WBT equivalent radius was calculated from the intersection of reservoir top and horizontal plane through the well bottom. Corresponding to WBT equivalent radius, cumulative gas production at WBT was found from the correlation. WBT can then be back calculated from cumulative gas based on gas production targets. WBT was predicted for multiple wells for multi-reservoir gas field with single producers. Actual WBT closely matches with the predicted WBT validating the proposed methodology for future applications. This methodology provides vital inputs for optimizing production strategy and surveillance plan to extend the field life and improve recovery. This methodology is found particularly useful in dealing with the field with multiple reservoirs with single producer where managing life of each well is critical. Since this methodology is based on analytical approach, it does not account for reservoir heterogeneities, interference with other wells, coning, fingering etc. Regardless of the limitations, this method can effectively predict water-breakthrough time in single well reservoirs. This novel water-breakthrough prediction method uses analytical model instead of numerical models proposed earlier. Hence, this approach requires limited inputs and simplified workflow. Considering reasonably accurate prediction of WBT, it can be used as primary input for optimizing production strategy. Further integration with the reservoir simulation model will be advantageous.