First Dual-Target Horizontal Appraisal Well-Geosteering in Thin Siliciclastic Reservoir of the Mauddud Formation, Sabriyah Oil Field, North Kuwait

Abstract

Since, the discovery of the Mid-Cretaceous Mauddud formation in the Sabriyah and Rhaudhatain fields of North Kuwait, there has been an interest to systematically produce the thick (> 400 ft) carbonate-dominated section, which has a complex geological setting that influences the performance of these reservoirs. Several wells have been drilled in the past-deviated, vertical, and horizontal wells focusing solely on the carbonate-dominated reservoir section with little emphasis on the siliciclastic shoreface facies of the lower Mauddud formation.The use of state-of-the-art real-time logging-while-drilling (LWD) data from the distance-to-boundary (DTB) resistivity mapping technique coupled with normal triple combo LWD formation evaluation log measurement and real-time pressure and mobility estimations provides insight into the lateral facies changes and the heterogeneity of the MaH reservoir layer for the first time.The predominantly carbonate Mauddud formation stratigraphically overlies the greater Burgan member. It was deposited in a low-to high-energy shallow marine ramp setting. The high-energy facies at the base is punctuated with out-of-sequence siliciclastic influence marking the waning of the deltaic Burgan sand influx. The upper part of the Mauddud formation is a highly diverse suite of low-energy carbonate facies characterized by highly bioturbated and reworked massive beds of wackestone and packstone with few depositional textures. This section is overlain by the prograding clastic sediments of the Wara formation and capped by the extensive transgressive shale of the Ahmadi formation.Well A (SA-0X05), the appraisal well, was planned to cut across all the Mauddud 10 reservoir layers and go lateral into the MaH reservoir with 100% NTG, thus yielding maximum reservoir contact (MRC) to evaluate this sand body for the first time. The results from porosity measurement validated the static model for this interval, and the pressure regime and mobility where inline with predicted values considering vertical variations. Lateral facies changes were observed showing coarsening-upward, clean-grained facies towards the base and the fine-grained glauconitic facies on top. Although an approximate20-ft thickness of sand was observed as a correlatable sequence from offset wells, in reality, geosteering revealed that the lower 15 ft of section was mostly distal in origin and changed to a more marine offshore facies below.