Experience of Low Salinity Water Flooding in Mumbai High Field - First Offshore Field in India to Implement Enhanced Oil Recovery Technique

Abstract

Abstract Low Salinity water flooding (LSWF) is a potential method for enhanced oil recovery (EOR). Lab and simulation studies of U-III reservoir in Mumbai High field indicates that the reduction of injection water salinity results in significant increase in oil recovery. On the basis of these studies, LSWF has been started in large pilot area in carbonate X1 layer of U-III reservoir in Mumbai offshore. In Mumbai High Field, U-III reservoir has been under conventional sea water flooding for pressure maintenance and better volumetric sweep which has yielded nearly 30% recovery over the past 4 decades. In search of feasible EOR process for further increase in recovery, numerous studies have been taken up in the past but high temperature, high salinity and pressure were major challenges in application of conventional EOR towards field implementation in Mumbai High. In addition, offshore conditions and multilayered reservoir with vertical and horizontal heterogeneity makes implementation of any EOR process even more challenging. After screening many EOR processes, low salinity water flooding was found to be most feasible solution which is environment friendly, cost effective and comparatively easy to implement in offshore conditions considering vast network of injection infrastructure (pipelines, facilities) already existing in Mumbai High. Over the past two decades there has been significant growth in evidence supporting the use of low salinity water flooding as a viable EOR method. LSWF unlocks oil by improving microscopic and macroscopic displacement efficiency. It involves physical (such as fines production that can block high permeable zones thereby increasing sweep efficiency) and/or geochemical process involving complex Crude Oil-Brine-Rock (COBR) interactions. Decrease in residual oil saturation is due to resultant change in rock wettability (more water wet) thereby enhanced oil recovery. In cases worldwide, LSWF can improve the oil recovery by almost 5 to 10% as per core displacement studies and few field pilot tests. This paper discusses the entire workflow adopted starting from EOR screening, Core studies, identification of Pilot area, Simulation studies and subsequent field implementation as a multiwell pilot. Further, the surveillance mechanism has also been discussed in this paper. The results of this pilot project will be a torch bearer for ONGC to implement LSWF in entire Mumbai High field in future.