Delineation of the Key Architectural Elements a Deep-Water Leveed Slope Channel Complex With Offset-Stacked Channel Elements, Tano Basin, Ghana: Development of an Integrated Geological and Geophysical Workflow for Reservoir Model Implementation

Abstract

The Enyenra field is located in the deep-water Tano Block offshore Ghana. The field, on production since August 2016, utilises a line-production system of alternating water injectors and producers. Most wells have vertical trajectories which intersect highly-heterogeneous, stacked sand-prone channel axis, thinner-bedded channel margin, and fine-grained channel levee deep-water facies, in a narrow (<2km) and long (>30km) belt with highly sinuous channel complex reaches alternating with straight ones. NW-SE orientated, buried Aptian faults exerted significant control on the planform channel sinuosity. The Upper-Turonian channel belt has intertwined, often highly sinuous, shoestring channel axis bodies with either vertical or high angle lateral stacked trajectories, causing significant challenges for designing water flood strategies and optimal hydrocarbon extraction. Rock Physics analysis of the reservoir and sealing facies indicated that an EEI80 impedance volume would serve as a strong lithology discriminator. Seismic imaging of the reservoir section, with overburden complexity, was optimised by Kirchoff TTI PSDM data processing. However, instances of non-flatness and distorted amplitude response of traces within gathers remain. This impacts the accuracy of the inverted data, which is the key tool for gross sand package delineation and net sand prediction. An integrated workflow was developed whereby axis, margin and levee facies belts could be confidently delineated along the full extent of the Enyenra channel complex: Well control, stratal surfaces and geo-morphological detail gleaned from the near-stack seismic (PaleoScan), and the EEI80 lithology discriminator, were used to demarcate facies belts on strike sections. These picks were further refined by using them to guide mapping of the respective facies belts, in a spatially-consistent manner, on stratal slices through the reservoir section. The facies belts, demarcated as polylines, were uploaded to the static model as a basis for the geo-statistical population of petrophysical parameters, appropriate to each of the respective facies belts. Interpretational uncertainty was incorporated by means of “mid-” and “high-case” scenarios to define the extent of margin facies on each flank of the channel complex. The strength of the workflow is the combination of high-end geophysical techniques with strong geological conceptual steer to derive products directly to a static reservoir model.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018