Integrated Approach in Optimizing Well Placement within Complex Turbidite Channels-Levee Systems in the Niger Delta Basin

Abstract

Well placement within thin and discontinuous reservoirs continues to prove challenging in present-day field development. Some geological objectives require draining accumulations within discontinuous reservoir fairways with thin true vertical depth (TVD) thickness (<7 m). The ability to geosteer within these complex systems using modern azimuthal tools has provided some solutions; however, there are multiple other elements contributing to successfully landing a drain with such reservoir scenarios. Turbidite channels are common within the offshore Niger Delta systems and in many other basins. The Niger Delta Basin is predominately a clastic system, and the reservoir targets in this fairway are a mix of structural and stratigraphic traps made up of sand and shales deposited during the Early Pliocene period. These systems are generally described as turbidite channellevee complexes. This paper discusses a case study using two recently drilled wells to analyze the technique/approach used for a successful and safe well placement operation. This approach involves two parts: the use of technology (geosteering tools) and the role of communication for a successful well placement operation. The primary tool used was azimuthal deep resistivity, which uses resistivity contrast within beds to help geosteer and stay within reservoir bodies, hence optimizing well placement. Guided by azimuthal resistivity imaging, it was possible to determine the well direction relative to the beddings using oriented binned data and resultant images. The communication aspect involved prejob, on-the-job, and post-job elements that contributed extensively to successful operations. A closed-loop approach to decision making was implemented whereby azimuthal resistivity data (and geosignal ratio curves) were measured and transmitted in real time, then analyzed by a team in the office collaboration room who transmitted information back to the rigsite for implementation. This paper also documents the uncertainties associated with the measurements and the processes available to mitigate them as well as lessons learned. Two wells were placed within undrilled fairways with reservoir and depth uncertainty. With the help of pilot holes 6 and 7-m TVD thick, hydrocarbon sands were discovered. Drains of 400 and 700 m were placed within these fairways, and each well exhibited good productivity. Interpretation of geosignals measured while drilling along with real-time follow-up on the seismic and knowledge of the geological setting were instrumental in the successful placement of these producing wells. The decision-making and analysis process was optimized, thereby achieving operational excellence (health, safety, and environment and timing) and cost savings. The most significant element of these operations is communication. The ability to analyze information and implement decisions rapidly involved all essential disciplines from service company personnel to drilling and completions to geosciences. Advancements made in geosteering technology and lessons learned from this case study can be applied to future well planning for geological targets originally assumed to be difficult, impossible, or too thin to be successfully drilled to increase field productivity.