--> Impact of Geological Heterogeneity on Recovery Efficiency in Deep-Water Reservoirs: Insights From an Integrated Subsurface (Wilcox Fm.) and Outcrop (T. Karoo) Study

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Impact of Geological Heterogeneity on Recovery Efficiency in Deep-Water Reservoirs: Insights From an Integrated Subsurface (Wilcox Fm.) and Outcrop (T. Karoo) Study

Abstract

Over the past decade several hydrocarbon discoveries have been made in the subsalt Palaeogene Wilcox play (Gulf of Mexico). Oil production exceeding expectations have commenced for a few years but a large part of the prospective area is situated below a vast and thick salt canopy severely limiting imaging and characterization of the producing units. Defining and distinguishing critical architectural styles (lobes vs. channels) is crucial for predicting the lateral continuity and vertical connectivity of deep-marine reservoirs. Submarine lobes are volumetrically the most significant building blocks in the basin floor Wilcox deposits but unfortunately these sheet-like units are hard to characterize based on seismic data alone. Other techniques such as well and core-based reservoir characterization and utilization of analogues are therefore essential. In this contribution we present how conceptual models for channelized lobes and criteria for interpretation of depositional environments can be tested in the distal Wilcox setting. Further we show how such an interpretation can help interpret production data and potentially simplify extensive history matching of reservoir parameters. The analysis was made using outcrop-based geological models where subsurface data from a Wilcox field have been coupled with outcrop data from Tanqua Karoo area, South Africa. The models were built using novel reservoir modeling techniques which enabled realistic representation of both the hierarchical build-up and the compensational stacking pattern of lobes. Sub-models reflecting proximal, lateral and distal depositional settings were selected and used to study how the character, geometry and spatial arrangement of depositional facies control reservoir performance. The aim was to test how production could vary depending on where in the fan system the reservoir is located, and understand if the wells are producing from sweet-spots, poor zones or intermediate areas. The results show that depositional settings and resultant facies types have significant impact on production/injection rates, optimal number and location of wells and recovery factor. The study show that identifying the good quality facies (sweet spots) is important to optimize well placement and increase the recovery as there is a severe economic limitation on the number of wells a project can support in deep-water setting.