Geosteering within thin clastic reservoirs can be extremely difficult due to their varying thicknesses, lateral facies changes and changing channel geometry. The efficiency of traditional triple-combo tools does not help achieve this objective due to their lack of azimuthal sensitivity. This paper presents a case history of reservoir navigation within a clastic reservoir in Saudi Arabia utilizing deep azimuthal resistivity, reservoir navigation modeling, and multi-component while drilling (MCWD) resistivity inversion.A number of challenges needed to be overcome for this well to become a successful oil producer. Firstly, the development and lateral continuity of the reservoir sand was not guaranteed. Reservoir sand developed at the bottom of the formation in all nearby offset wells. The development in the upper part of the target formation however, varied throughout the field. In addition, further uncertainty was present regarding position of the oil-water contact (OWC).A reservoir navigation strategy was devised utilizing a full triple combination of logging while drilling (LWD) tools that included deep azimuthal resistivity and azimuthal density. In addition, MCWD resistivity inversion software was used to ascertain the resistivity of the shoulder beds through inversion of real-time resistivity and azimuthal resistivity curves. The reservoir navigation strategy comprised maintaining a well inclination of 85 degrees until a clean reservoir sand was penetrated. MCWD would provide the first indication of the approaching reservoir, and well inclination would be increased in anticipation of reservoir entry. Upon entry in the reservoir, the deep azimuthal resistivity data, used in conjunction with reservoir navigation, would keep the well in the reservoir until TD or until the sand pinched out. In addition, MCWD would be used to ascertain the lower conductive boundary resistivity, either shale or water.This strategy was successfully implemented and resulted in 1,400 ft of reservoir contact, achieving 100% Net: Gross. The deep azimuthal resistivity prevented reservoir exit in spite of higher-than-anticipated formation dip and a thinning reservoir towards the toe of the well. MCWD successfully proved that the lower conductive boundary was shale, not water, and confirmed the distance to the boundary results from the deep azimuthal resistivity tool.

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Reservoir mapping is growing rapidly, especially for complex reservoir systems, due to the global need for enhancing fields' production. For mature fields, the uncertainties in the geological structure and water encroachment in the active reservoirs are two major concerns in field development programs. Both play important roles in reducing the overall hydrocarbon production potential of wells and can result into a drastic recovery drop due to premature drainage of the reservoirs.Al-Khafji Joint Operations has drilled several wells in its main offshore field targeting a fluvial channel depositional environment that consists of alternating beds of sandstone and shale and reveals high lateral heterogeneity in reservoir position as described by existing log correlations. Moreover, some wells show a water signature within the main hydrocarbon-bearing interval although the addressed water contact is much deeper. These wet intervals are attributed to water fingers and can hardly be correlated throughout the field.Remote identification of the reservoir characterization and successful wellbore placement relative to the water encroachment would extend the production life for those related producers. Placing and completing horizontal wells within this complex reservoir system without the plan to drill pilot wells poses a particular challenge. The existence of laterally complex heterogeneity will make it very difficult to place the well even a short distance away from an existing offset well.Deep directional resistivity measurements of up to 100 ft radially from the wellbore have helped to overcome the challenges of placing wells and characterizing the reservoirs within such structural, stratigraphic, and fluid uncertainties and added to the completion strategy. Practicing this technique has helped to eliminate pilot wells without impacting the success of the delivery of these wells, thus increasing the time and cost efficiency of the overall drilling operations. Oil columns ranging between 20 and ϩ80 ft thickness with underlying water contacts were mapped along with reservoir and fault geometry. The reservoir mapping application therefore facilitated improved understanding of the overall reservoir; structure, fluids, and lateral heterogeneity.