Thin Sand Development Made Possible through Enhanced Geosteering and Reservoir Planning with While-drilling Resistivity and NMR Logs: Example from Niger Delta

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe horizontal well placement within a thin sand with structural dip and economically produce these reserves are a challenge for the oil industry. New Reservoir Management and Formation Evaluation techniques are making these very thin hydrocarbon sands accessible and economic for development. Upfront planning by multi functional team to define well placement, uncertainty management and tool selection are key. Next execution of landing and lateral require maximum flexibility and accuracy from tools and team.In this paper, two case studies are presented where Logging-While-Drilling (LWD) resistivity and Nuclear Magnetic Resonance (NMR) were utilized to geosteer a horizontal section through a thin sand and to geo-stop the horizontal well after drilling an optimal drain hole length.Resistivity and NMR-LWD provides critical formation evaluation information such as resistivity at bit, up and down resistivities, structural dip, formation porosity, bound-fluid volume, free-fluid volume and permeability.Obtaining this information while drilling has a significant impact on drilling and completion decisions in Niger Delta. In the first case study, based on the information of NMR LWD from a pilot hole, a horizontal sidetrack was optimised in the high permeable section of the thin reservoir. In addition, NMR logs demonstrate the horizontal section was placed generally within the sweet spot of high free fluid section.Drawing experience from the first case study, a more difficult situation of drilling a horizontal well with a six feet window was addressed. The objective was to place the well within the sand and drill an optimal length that will meet hydrocarbon deliverability. First, resistivity at bit was used to restrict the well within the target sand. Within this heterogeneous sand, the while-drilling resistivity image and up and down deep Resistivity measurements allowed the geosteering team to stay in the "sweet spot" of the reservoir.Concurrently, permeability was estimated from the NMR log. Based on this permeability, hydrocarbon producibility was computed and decision was reached to drill the optimal length. This novel approach combining geosteering techniques using flexibly LWD tools are key to future development of thin hydrocarbon reservoirs.