Coiled Tubing Sidetrack: Slaughter Field Case History

Abstract

Summary The paper describes the successful sidetrack of an oil well in the Slaughter Field in West Texas using coiled tubing (CT). Several first-time CT operations performed during this workover include: Setting a whipstock in casing on CT Cutting a window with CT Using measurement-while-drilling (MWD) with CT in a "real" well Use of a fluid-operated orientation tool for in-hole tool face changes Successful use of an "autodriller" to maintain weight on bit while drilling Directional control of the sidetracked hole proved to be ineffective due to a surface software problem. The resultant wellbore was not horizontal as planned, but instead closely paralleled the original well for much of its length. However, the previously non-productive well flowed 1000 barrels of fluid per day (BFPD) from the sidetrack following the workover. Introduction The Slaughter Field is located in Cochran County, Texas, approximately 50 n-tiles southwest of Lubbock (Figure 1). Production is from the San Andres formation (dolomite and anhydrite) at true vertical depths (TVD) of 5000 - 5200 ft. Most producing wells are on rod pump. The subject well, H.T. Boyd 59X, had been drilled to a total depth of 5245 ft MD (measured depth) in 1989 as the center well (producer) in a five-spot waterflood pattern. The well failed to produce significant fluid volumes during initial completion attempts. Stimulation with acid and a subsequent fracture treatment failed to significantly open the well up. It tested 64 BFPD with 6% oil cut following stimulation (producers in the area generally produce in the 400 BFPD range) and was shut in until initiation of sidetrack operations in July, 1992. PLANNED ACTION Using CT, it was planned to sidetrack the well to a bottom hole location (BHL) approximately 700 ft. to 900 ft. NNW of the original BHL. A build rate of 15/100 ft. would be required to yield 500 ft. of horizontal section in the pay zone. Planned TD was 5850 ft. MD (5052 ft. TVD) (Figure 2). The 3.75 inch hole was to be left uncased and the well produced on rod pump, as required by most wells in the reservoir. DESCRIPTION OF THE CASE HISTORY WELL Prior to the workover, the Boyd 59X well was cased with 5-1/2 inch outside diameter (OD), 15.5 pounds per foot (ppf), J-55 casing set at 5245 ft. A cast iron bridge plug had been set at 5030 ft. with +90 ft. of cement on top of it following unsatisfactory completion attempts in the interval 5082 ft. - 5165 ft. MD. The well had an inclination of approximately 14 at the projected window depth of 4845 ft. MD. Direction of the wellbore at this depth was 3461 (Figure 3) DISCUSSION OF FIELD OPERATIONS Rigup A detailed CT drilling plan for the sidetrack was prepared by the coiled tubing service company and the operator.