Coiled Tubing as Initial Production Tubing: An Overview of Case Histories

ABSTRACT From January, 1993 through July, 1994 Marathon Oil Company completed ten newly drilled gas wells using coiled tubing as the initial production string. This paper reviews the operational aspects of each job and summarizes the areas where improvements in equipment and technique were implemented. The use of coiled tubing allows the tubing size to be closely matched to the performance of these relatively low rate wells, minimizing the tubular costs and improving the well's ability to stay unloaded. The main areas of improvement from one job to the next involved the use of a pressurized, hydraulically operated access window, ensuring that all frac sand was cleaned out prior to landing the coiled tubing and employing a "hot cut off" system to make the final cut on the coil tubing. Lessons learned include keeping the coiled tubing size large enough to run smaller coiled tubing through it for clean out and slickline work, care in closing the BOP rams to avoid damaging the pipe and the use of wellhead equipment specifically designed for coiled tubing. This technique is especially suited to low pressure and water sensitive reservoirs where loss of fluid is of concern. An additional benefit is the cost savings from reducing the hole and casing sizes to match the reservoir potential. This completion technique is often quicker than using a conventional completion rig and jointed tubing. INTRODUCTION Marathon has used coiled tubing for initial production tubing in several wells in order to match the tubing to the well productivity, unload frac fluids as quickly as possible and to minimize cost by reducing the time the drilling rig stays on location. An additional benefit is that no fluid is lost to the formation during the completion.