--> Generating Value Through New Logging Technology and Analytical Methods — Case Study From Offshore West Africa

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Generating Value Through New Logging Technology and Analytical Methods — Case Study From Offshore West Africa

Abstract

The West Africa basin encompasses a vast diversity of geological depositional settings, in and from which hydrocarbons are being explored and produced. Offshore, Cretaceous aged turbidity slope-channels and fan systems still prove to contain volumetrically significant oil and gas reservoirs. An intelligent petrophysical evaluation is essential to enable most adequate development and production strategy to be deployed. The siliciclastic rock units can be structurally heterogeneous, the reservoirs distribution and quality highly variable, making it hard for conventional logs data to pick potential reservoirs with pay. The paper illustrates remarkable examples of intelligent logging assessments in highly complex reservoir units with focus on successful application of novel technology deployed in effective and efficient fashion. This reservoirs have variable thickness and generally medium permeability (200-800 mD); but silt and clay laminations and tight material are affecting the reservoir quality in some layers, resulting in changes in the well productivity and sweep properties. The fresh to very fresh formation water environment diminish the contrast of water to hydrocarbon making it difficult for any salinity based measurement technique, like resistivity to easily unravel hydrocarbon bearing intervals. Besides, some of the reservoirs are stacked sand bodies with varying salinity values among the different hydraulic units and cannot be accessed by conventional logging open hole conveyance. Novel dielectric dispersion and high definition spectroscopy technology are game changers in their respective range of applications. Whether run in combination with other measurements and analyzed in integrated approach or as standalone analysis if need arise, the appropriate use of those techniques highly reduce uncertainty of hydrocarbon volume and net producible fractions. Comparison of the formation evaluation results to actual well testing confirms the improvements in reservoir description from the addition of the advanced logging measurements (at early stage of reservoir development) into reservoir models. The information provided guide optimal perforation and completion design and help defining future field development plans.