A FEASABILITY STUDY OF EXTENDED REACH WELL, VARG 15/12-A-11 A
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This report is an analysis of an extended reach drilling (ERD) well planned to be drilled from Varg A to the Rev East reservoir in the North Sea. It is a continuation on the torque and drag (T&D) analysis “Torque and Drag Analysis for Extended Reach Well 15/12-A-11A” written by the same author. Proper T&D analysis is determining for good ERD drilling practices. The T&D analysis is showing that torque values in the 8 ½” section are substantially high and that buckling of the drillstring is likely to occur in that same section. However, ERD challenges are numerous and not only limited to T&D. To create a more realistic picture of the well it is essential to perform a hydraulics analysis including other elements such as hole cleaning, equivalent circulating density (ECD) management, the running and cementing of casing and standpipe pressures. They are all key issues that must be planned for and evaluated in order for the well to be a success. The software WELLPLAN has been utilized to do a proper hydraulics analysis of 15/12-A-11 A. The report is set out to present this complex well analysis as simply and structured as possible. 15/12-A-11 A is an 8000 m, almost horizontal well which means higher torque, more drag, more complex hole cleaning, higher surface pressure and higher ECD fluctuations. One of the main purposes of this report is to identify what special operational demands are set to the rig drilling 15/12-A-11 A when looking at hydraulic and T&D requirements. By doing simulations in WELLPLAN the goal is to capture the best practices for complex ERD planning and drilling of 15/12-A-11 A. Drilling this well would require excellent engineering skills, alternative drilling strategies and significant planning to implement real optimization to the drilling performance. New achievements in ERD drilling are demonstrating that it is possible to exceed the current ERD experience with existing technology. Relevant technology for 15/12-A-11 A is being evaluated in this report. After the T&D study in “Torque and Drag Analysis for Extended Reach Well 15/12-A-11A”, high torque in the last 8 ½” section was considered the major operational challenge. However, after performing a hydraulics analysis of 15/12-A-11 A it is found to be more than one major challenge for drilling this complex ERD well. Several different well scenarios have been modeled with focus on standpipe pressures, ECD and flowrates for efficient hole cleaning.The major risks with respect to hydraulics found for 15/12-A-11 A are high ECD fluctuations in the reservoir section, exceeding standpipe pressure and challenging hole cleaning due to thehigh well inclination and a small annular flow area. The well was initially planned with only two hole sections, the 12 ¼” and 8 ½” section. However, due to the low reservoir pressure at Rev and the high ECD in the 8 ½” section,another hole section has been suggested added to the existing well profile. This is in order to reduce the high ECD in the 6” reservoir section allowing for a lower drilling fluid weight, hence reducing the high over balance in the reservoir and minimizing the risk of fracturing the formation. An extended T&D analysis, together with procedures for running and cementing the casing and the two liners have been included in the final analysis of 15/12-A-11 A.