Hybrid System Brings Flexibility of CT to Long, Extended-Reach Wells

Abstract

This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 142769, ’New Hybrid System Brings the Flexibility of Coiled Tubing to Long, Extended-Reach Wells,’ by F. McNeil, SPE, S.D. Lindsay, SPE, R. Lyons, and R.P. Gracey, Halliburton, prepared for the 2011 SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, The Woodlands, Texas, 5-6 April. The paper has not been peer reviewed. The number of long extended-reach wells being drilled in the oil and gas industry continues to increase. These wells present complex challenges in completion and intervention procedures because operators demand the same level of performance achieved on shallower wells while providing a cost-effective and safe solution. To reach deep target depths with coiled tubing (CT), smaller coil must be used because of reel capacity, which limits pumping rates because of pressure and velocity limitations. As an alternative, jointed pipe can be used; however, using jointed pipe reduces the overall efficiency of the process because continuous pumping cannot be achieved. A new hybrid system uses both CT and jointed pipe in a single work string. The system incorporates a unique flapper safety valve that enables seamless functioning of the string in a live well. The hybrid system enables larger CT and jointed pipe to be deployed, which results in higher pumping rates and greater depths. Large CT Reel Capacity. A major hurdle when considering large lengths of CT is reel capacity. For example, the maximum length of coil that can be stored on a standard reel [assuming 144-in. reel outer diameter (OD)] is as follows: 1¾-in.-OD CT: 19,670 ft 2-in.-OD CT: 14,795 ft 2⅜-in.-OD CT: 10,151 ft Lockup. Another important consideration in the design of any CT job in a highly deviated deep-reach well is lockup. Lockup occurs when CT forms a helix inside the casing and high wall-contact forces prevent any additional forward movement. While this effect will occur in all CT, smaller CT is more susceptible to complete lockup at shallower depths than larger CT. Therefore, larger CT is more likely to reach target depths. Wellbore Cleanouts. Accumulation of sand and solids in wellbores significantly impairs oil and gas production; an influx of sand can impair or stop the flow of oil from a reservoir. This is commonly dealt with by CT intervention; in fact, nearly half of all CT operations involve well cleanouts. Conventional CT units are limited to small-OD coil when performing remedial operations on deep wells because of limitations in reel size, as well as local laws regarding width, height, length, and weight restrictions.