Complex Deepwater Reservoir in the Niger Delta

Geological and geophysical uncertainties account for most of the challenges encountered during the placement or geosteering of high-angle and horizontal wells in deepwater environments. Structural uncertainties could result from the targeted subsurface structure that is folded, undulating and faulted. Lateral discontinuity of sand bodies, lateral variations in sand thickness, multiple beds, and formation heterogeneities are some of the more common sedimentological uncertainties. Geophysical uncertainties include the vertical depth of the seismic data and seismic reservoir characterization. These uncertainties make increasing the likelihood of success during geosteering not only dependent on the integration of geologic and seismic reservoir characterization techniques, but also on the application of a robust reservoir navigation scheme. This is a case study of the geosteering of a horizontal producer well in a complex reservoir in the deep offshore Niger Delta. The reservoir consists of highly faulted channelized turbidites. The lateral discontinuity of sand bodies and the variations in sand thickness have been calibrated by other producer wells in the field. For efficient geosteering, geological and geophysical well planning was complemented by the availability of scenario modeling, a suitable drilling strategy, the availability of fit-for-purpose drilling and formation evaluation tools, robust software, and a multidisciplinary team with the right mix of experience for effective reservoir navigation. An extra-deep azimuthal resistivity tool was used, and the inversion was performed with Multi-Component While Drilling (MCWD) software. The study reviews the geological and geophysical strategies employed during the geosteering, examines the role the extra-deep azimuthal resistivity inversion modeling and borehole imaging played in understanding the nature of the reservoir.