Marginal Field Water Flood Management Combining Strategic Planning and Cost-Effective Solutions

Abstract The case study relates to a marginal green field located in the shallow waters, offshore Abu Dhabi. The target reservoir consists of layered and heterogeneous Jurassic carbonates encountered at about 10,000ft subsea. The field is a four-way structural closure with about 26km2 area and 340ft structural relief, with a weak edge aquifer. After three years of primary recovery, the field is under peripheral water flood for the past two years. It is currently in the voidage filling stage; downhole gauges supporting a correction of the pressure decline experienced during the natural depletion. Integrated waterflood management deployed the following processes and technologies: Filtration treatment of source waterStrategic revision to injector placementWaterflood monitoring by tracers, ILT/PLTs and downhole pressure gaugesFluid compatibility and core flood experiments for potential formation damageProduced water management through disposal well Sea water was treated by membrane filtration technology to the following specification:98% removal of particle size 2 micron and aboveturbidity 0.1TSS 0.1 mg/lMillipore 6 l/30 minOxygen content 10 ppb Injection support and pressure maintenance was monitored by downhole gauges. Zonal flow contribution was assessed utilizing injection/production logging tool. Low cost and environment friendly inter-well chemical tracers were deployed to monitor injector-producer connectivity and water breakthrough. The results and findings presented below are expected to benefit the practicing engineers and geoscientists while developing marginal fields. Peripheral injection and injection into the water leg was found less effective. This offered suboptimal energy support due to i) deteriorated aquifer properties, and ii) injected water requiring to travel long distance causing delay in pressure support. Subsequent injectors were placed in the mid-flank region inside the oil leg to mitigate the effect of areal and vertical heterogeneity. Barring the initial flow line debris, the filtration treatment had maintained the water quality to specification. Zonal time-lapse pressure data suggested the field was well connected laterally, however individual layers were depleting and flooding differentially due to strong permeability contrast. Core flood experiments and mixing of injection and formation brines did not reveal any risk of permanent pore throat damage due to scaling or fines migration. Inter-well tracers offered exceptional means to monitor the injector-producer connectivity, identify source well and time of injection water break through. Water breakthrough was observed at 75 to 545 days after injection and correlated with the well spacing and voidage fill. Water loading in the producers was complemented by onset of a declining pressure trend. Hall plots showed variable injection efficiency with some wells showing stable injection and others with positive skin or injection out of zone, requiring further investigation and remedial. Produced water was disposed to a shallow subsurface stratum to minimize cost and environmental impact.