Loss and restoration of water coning control – field case history and prediction
Andrew K. Wojtanowicz, Lu Jin
Vol. 35, no. 1 (2018), pp. 343-359, [1]
It is well known that water coning is a difficult-to-solve problem in heavy oil reservoirs with bottom water. A promising solution is offered by the downhole water sink (DWS) technology – a dual well completion technique for water coning control in reservoirs with bottom aquifer. In the field case addressed in this study, a DWS well was installed in a heavy oil reservoir underlined by thin water zone – notorious for severe water coning problem. Initially, the two well’s completions had no separating packer; Later, the well was recompleted with packer and displayed much improved oil productivity and water coning control. However, after accidental shutdown of the bottom (water sink) completion and continuing production from the top (oil pay) completion the well was rapidly watered out and shut down. In this study, the well’s production history is analyzed to better understand dynamics of water coning control with packer-less DWS and the effect of temporary water sink shut-down. The analysis is performed with a radial grid-based simulation model using the reservoir properties and well production data. An adequate history match is achieved by tweaking reservoir properties within their uncertainty range – mostly the relative permeability and capillary pressure curves. The packer-less completion displays steady invasion of water to the top oil completion through the gravel pack with no separating packer. The analysis also confirms detrimental effect of sole temporary shutdown of the water sink (bottom) production that caused rapid buildup of water saturation in the oil pay zone around the well. This work also evaluates possible restoration of oil productivity by putting the well back on production after a dormant period of time (when water cone might subside) and the contribution of the bottom water drive (aquifer strength) to the restored productivity. A 25-year production performance forecast is performed for three scenarios of well’s operation after the water sink completion’s shut-down for one month: (a) no shut-down and continuing production as DWS well; (b) one-month shut down and conversion to a conventional single-completed well; (c) one-month shut down and continuing production as DWS well. The results reveal that the watered-out well could be revived as an oil producer only by restoring its DWS operation [scenario (c)] as the conventional well operation [scenario (b)] would produce only water. Moreover, detrimental effect of temporary water-sink shut down would irreversibly reduce well's productivity by more than 10 percent. It is also shown that stronger aquifer stimulates DWS well productivity improvement of up to 20 percent in case of strong bottom water drive.