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.
A preliminary sequence-stratigraphic framework for the Late Jurassic to Early Cretaceous section is interpreted using a regional 2-D seismic grid, four 3-D surveys and five deep wells. In local stratigraphy, the studied section covers the Middle Jurassic Dhruma, Sargelu and Najmah formations, the Upper Jurassic Gotnia and Hith formations, and the Lower Cretaceous Makhul, Ratawi Oolite and Ratawi Limestone formations. A total of eight sequences have been interpreted. After the detailed sequence interpretations, isopach maps of all the sequences are made. Based on these isopach maps, the stratigraphic relationships observed on seismic and well data, the interpreted sequences could be grouped into Sargelu-Najmah transgressive/highstand composited sequences, Gotnia-Hith lowstand composite sequences, and Makhul-Ratawi transgressive-to-highstand composite sequences. The isopach map of the Sargelu-Najmah composite sequences showed that a local carbonate platform in the southwestern part of PZ area was built-up on a potentially low-relief high on a previous ramp setting. The platform kept up with the sea-level rises and eventually a highrelief platform was formed. The Gotnia-Hith composite sequences are mainly composed of salt and anhydrite, which filled the topographic lows and pinched out against the Sargelu-Najmah carbonate platform. A subsequent transgression and highstand during the Makhul-Ratawi depositional time further flattened the topography, and a ramp setting was formed again. As a result of this study, depositional facies, the history, and reservoir distributions could be better interpreted with the calibration with wells. The results showed that most of the depositional facies distributions within this period were not affected by current local structures, consistent with the conclusions made by Kelsch et al. (2013) that the current structures hosting the major fields in the PZ area were actually generated by middle-late Cretaceous age tectonics.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.