Abstract

Sabiriyah Upper Burgan is a multilayer clastic reservoir in North Kuwait under active water flood since 2000, which has been rated as one of the most heterogenous reservoirs as per analogous studies in the past. With five major flow units, poor sweep efficiency often results from spatial variation and/or heterogeneity in the permeability of the reservoir rock, usually resulting in an irregular displacement front of the injected fluid. The initial completion design did not address the injection profile control. Also, conventional techniques to improve vertical conformance did not give desired results. The objective of using Water Flooding Regulator (WFR) is flooding all the units so as to improve the overall sweep efficiency.

To optimize vertical & areal sweep efficiency and enhance production from the uncontacted portions of this reservoir, a paradigm shift in water flood strategy was adopted for selective injection strings using WFR. These devices[RAJ1] enable to control injection rates in specific layers irrespective of the reservoir pressure, permeability, skin damage or any other factors that would normally affect flow, focusing where the oil needs to be swept. The new completion design with WFR was installed in one of the water injector wells, thereby recompleting the well, switching from the conventional to the straddled packer completion, grouping five flowunits into three zones with WFR, rationalizing the splits as per needs per layer vis-a-vis to the perforations in nearby producers.

Prior to the installation of the WFR, surveillance actions such as re-perforation, ILT and injectivity test, were conducted. Workover rig was deployed with an integrated plan for running the completion. Since three units have been grouped in one zone, allocating the water in each unit during the design stage itself was done as per the best reservoir management practice involving all stakeholder teams.

The first implementation of WFR in Kuwait, has proved the concept of improving vertical injection profile by enabling higher injection rates into layers that never received water before and regulating the distibution into all layers. As most of the water injected into the well (more than 90%) was traversing through one zone only before the job, the vertical distribution of injected water due to WFR approach resulted in choking the flow through this layer to about 60% and improve the flow through the remaining uncontacted layers. In the long term, this approach is likely to to add to production, reserves and ultimate recovery factor.

Based on comprehensive evaluation, a campaign of completing nine more vertical injector wells with this selective-string design is planned by Kuwait Oil Company (KOC)[RAJ2][JMAR3]. The re-engineering of injection profile has paved the way for application of this technique in other similar reservoirs of Kuwait.

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