The knowledge of structural geology and depositional environment plays an important role in the success of any geosteering job. The bedding type, bedding dip and dip direction, faulting, localized folding, lateral facies change and continuity of sand bodies, sand-shale ratio of the deposits are some critical factors to consider in the planning of a geosteering job. These factors determine the predrill geosteering strategy and the real-time decision-making steps. The resolution of seismic data, the limited number of offset wells and their lack of proximity to the planned well, contribute uncertainty to the knowledge of these factors before drilling commences. This is a case study describing the geosteering of a complex deepwater turbidite reservoir in the Niger Delta. The reservoir is a sandy lobe deposit and is faulted. The well objective was to drain the required intervals in the sand compartments and geosteering was needed to support real-time decision making by estimating the throw of major faults, determining the presence of sub-seismic faults, interpreting near-wellbore structural geology, stating the proximity of conductive boundaries and describing reservoir heterogeneity. The geosteering was successful with the trajectory draining all planned sand bodies, providing improved structural interpretation of the reservoir geology in real time and achieving over 500m of net sand. The aim of this paper is to review the real-time decisions taken to achieve the well objective of placing a drain section in a sandy lobe deposit, describe the near-wellbore structural geology of a turbidite reservoir in the Niger Delta, and review some geological factors to consider while geosteering in deepwater Niger Delta reservoirs.

Variable reservoir thickness, heterogeneity, and presence of geological truncations are some of the challenges inherent in draining complex reservoirs. These challenges affect the depth of detection of some formation evaluation tools, the ability to optimally place the well in the target horizon, and the ability to remain in the sweet spot throughout the drain length. To mitigate these challenges, reservoir navigation service with fit-for-purpose tools and robust software is required. This paper is a case study of the application of the VisiTrak™ tool and Multi-Component-While-Drilling (MCWD) inversion software (Sviridov et. Al., 2014) in the geosteering of Well-X. VisiTrak is an extra deep-reading azimuthal propagation resistivity tool. MCWD is software that essentially creates a geological earth model from the readings of azimuthal propagation tools. It is multi-layer inversion software. Well-X is located in offshore Niger Delta and the target reservoir consists of several individual turbidite complexes and stacked channels. The successes recorded in this geosteering case include accurate subsurface structural interpretation, reservoir characterization, and achieving well objective in terms of net sand drilled. This paper demonstrates the importance of reservoir navigation in accurate well placement, the benefits fit-for-purpose tools bring to geosteering complex reservoirs in the Niger Delta and shows the value of data integration in reservoir navigation service.

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