Waterflood Pilot in a Mature Fractured Carbonate Reservoir

摘要

This study focuses on a giant fractured carbonate field in thernMiddle East where large undeveloped oil volumes reside in arnreservoir that is currently producing via Gas-Oil-Gravity-rnDrainage. An inverted five spot pilot is planned to address thernviability of waterflooding this reservoir, to increase productionrnrates and ultimate recovery.rnThree issues determine the success of waterflooding thisrnreservoir. Firstly, there is a sharp contrast between thernrelatively homogeneous and unfractured low-permeablernbottom part of the reservoir, which is the main target for waterrnflooding, and the heterogeneous, highly fractured upper part.rnSecondly, the ongoing GOGD development and the associatedrngas injection have resulted in considerable uncertainty in therncurrent oil and gas saturation distribution in the fractures andrnthe matrix. Finally, the uncertainty on vertical to horizontalrnpermeability has a major impact on the waterflood recovery inrnthe bottom part of the layer.rnReservoir simulation of a pattern element shows scope forrnan additional 20 % recovery in unfractured reservoir units.rnThis is limited mostly by the reduction in sweep efficiency duernto water shortcutting through the high permeable layer.rnAnother key uncertainty is free gas production caused by thernongoing GOGD development.rnThe results of the element model simulating a field widernpattern were compared with the results of a second unconfinedrnreservoir model representing the pilot five spot.rnThe unconfined pilot will show lower production rates thanrnthe full pattern development due to insufficient pressurernsupport. Not appreciating this phenomenon can causernunderestimation of expected pattern water drive performance.rnOn the other hand pattern drive performance can bernoverestimated on the basis of the pilot, since gas will migraternout of the unconfined pilot area and oil mobility in the pilot isrnless affected by the presence of free gas in the pilot.rnThe pilot five spot is currently being drilled and its resultsrnwill be used to predict performance of the full field patternrnwaterflood scheme.