ABSTRACT Early water breakthrough due to pressure depletion is often attributed to a strong water drive and must be established to avoid wrong reserves estimation and planning. In this study, we evaluated the Safsaf C reservoir, an undersaturated oil reservoir in North Africa that experienced early water breakthrough at 62 days after the commencement of oil production. To establish or disprove the presumption of it producing under a strong water drive, we critically analyzed the reservoir using the Material Balance Equation (MBE) coupled with the pot aquifer water influx model. The Campbell plot showed a weak aquifer, and the Solution plot confirmed aquifer presence. The pot aquifer plot gave the original aquifer in place an estimate of about 28.42 mmRB, which is about half the size of the estimated hydrocarbon pore volume of 51.15 mmRB. Water influx plots produced improved Oil initially in place (OIIP) estimates in the range of 11.50 to 12.20 mmSTB. The aquifer influx profiles show that water encroaches into the reservoir at a rate of 742 rbl/d. This approach is suitable when little is known about the aquifer and provides reliable estimates of OIIP and the degree of aquifer support for reservoirs bounded by small aquifers.
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