The CACT Operators Group planned to drill an extended-reach horizontal well to recover reserves in a thin reservoir layer approximately 2 m thick. This well, which was designed to complement an existing well, was to be landed in the structure's flank while turning. Then the well's horizontal section was to be drilled eastward, following the structural slope, for 400 m, the distance required to achieve the well's economic limit.
The biggest challenge was meeting the directional steering and well placement goals to land the 300-m section within the thin target zone. Drilling would be along a downdip followed by an updip and then leveling off at the minimum depth required for setting the 7-in casing shoe. The team had to avoid drilling into the tight calcite cemented streak in the upper part of the reservoir. Doing so could cause an instant drilling torque increase that would make it impossible to drill the production interval to the planned 400-m length.
The team used rotary steerable systems and advanced LWD technology, including PeriScope bed boundary mapping, EcoScope LWD, and adnVISION services. While drilling the landing section, PeriScope deep azimuthal measurements kept them informed about the distance to the reservoir boundaries, and EcoScope density images provided real-time formation evaluation and structural dip interpretation. In the horizontal section, the adnVISION service was used for formation evaluation, and the PeriScope mapper's ability to simultaneously delineate multiple boundaries enabled accurate wellbore placement within the thin pay zone without drilling into the upper reservoir hard streak—despite the structural uncertainties.
The actual structure updip began much sooner after the landing section entered the reservoir than the predrill model had indicated. However, using real-time PeriScope bed boundary mapping and EcoScope fullbore density images, the drilling team was able to adjust the trajectory smoothly with relatively low dogleg severity. This smooth adjustment minimized the accumulation of high drilling torque while keeping the trajectory within the porous zone and avoiding entering the tight calcite cemented streak in the upper part of the reservoir.
The actual structure found in the well's horizontal section varied significantly from the original predrill model, but the PeriScope mapper provided clear identification and delineation of the reservoir's top and bottom boundaries. This information made it possible to keep the well trajectory 0.5 m below the top of the pay zone without exceeding the drilling torque limit of 42,000 lbf.ft. After drilling 290 m of the lateral section, total drilling torque had reached nearly 41,000 lbf.ft. However, the well placement team extended the section an additional 125 m within the remaining 1,000-lbf.ft drilling torque window—15 m beyond the planned 400-m lateral length—by avoiding unnecessary trajectory adjustments.
Precise placement of the lateral producing section resulted in 100% net to gross, ensuring optimum reserve recovery. The well has been producing 2,000 bbl/d of oil with 0% water cut. Well test data showed that the well could have produced up to 4,000 bbl/d of oil, but CACT elected to limit production for reservoir management purposes.
