The paper presents a case study to improve recovery in a heterogeneous depletion drive oil reservoir by pressure maintenance through waterflooding, which was designed by analyzing seismic attribute and well tests data and incorporating it in a reservoir simulation model.

X Field is an undersaturated oil field which has been accessed by two wells. It is an extremely heterogeneous reservoir with X-1 being a prolific producer while X-2 having no production due to significant facies variation in the reservoir over a short distance (~2km). The field displays depletion drive behavior with rapid pressure decline over low recovery. A reservoir simulation study was undertaken to improve recovery and arrest pressure decline. Attribute analysis and well tests data helped address heterogeneity of the reservoir by predicting the facies distribution throughout the reservoir. These learning's were incorporated into a reservoir simulation model and a line drive water injection pattern was determined as the optimal method to improve recovery in X Field. A new well, X-WIW, was drilled to start injection and sidewall cores were acquired from it. Multiple lab tests were performed on these cores to confirm injected water compatibility with the formation while the well's injection rates and surface parameters were closely monitored to help minimize reservoir damage and achieve continuous injection.

Using seismic attribute analysis, a good facies zone was identified for drilling X-WIW for line drive water injection pattern. Well results showed good quality sand which laid further credence to the facies distribution model. MDT showed depleted pressure in X-WIW, therby confirming connectivity between X-1 and X-WIW. Sidewall cores were obtained and multiple tests performed, including Capillary Suction Test (CST), XRD Analysis, Sludge Test and Core Flow Test, which showed no presence of swelling clays and good formation compatibility with injection water. Prior to injection, X-1 was shut in to preserve reservoir energy and current bottomhole reservoir pressure was measured. Upon receiving these lab results, injection was initiated successfully, with X-WIW injecting 2500 bwpd while keeping X-1 shut-in. Periodic measurements of bottomhole pressure were taken at X-1 to observe injection response. The pressure at X-1 was measured to be steadily increasing indicating successful voidage replacement. The most significant new finding was the accurate prediction of the pattern of variation of petrophysical properties through seismic attribute analysis and well tests data which enabled X-WIW to be a successful injector and helped in improving the recovery of X Field.

Prior to this water injection project, X Field was predicted to have a recovery factor of 21% which has now been improved to 35%. This significant increase in recovery was made possible by the successful implementation of the water flooding project in a heterogeneous and stratigraphically complex field.

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