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. Many areas have road weight restrictions that will also dictate the size and length of CT that can be used. As an alternative, jointed pipe can be used; however, using jointed pipe reduces the overall efficiency of the process, as continuous pumping cannot be achieved.The new hybrid system uses both CT and jointed pipe in a single workstring. 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 depths. This reduces the overall job time, while improving safety and efficiency for deeper well applications, including multizone stimulation, cleanouts, drilling, and mill-outs. This paper presents the hybrid system design and benefits in multizone stimulation, drillouts, cleanouts, and other wellintervention applications. Also included is a case history to demonstrate the success of the system when applied in a multizone fracture-stimulation treatment. IntroductionCT is a vital tool for oil and gas operators to achieve safe, efficient, and effective well-intervention operations. Typically ranging beyond 25,000 ft in length and from 1 to 2.875 in. in outside diameter (OD), these continuous strings of pipe are uncoiled into live wells to perform milling, drilling, cementing, logging, perforating, fracturing, completion, or maintenance operations. Deeper well completions with extended-reach horizontal laterals have presented some unique problems to those seeking to perform well-intervention operations.
As the industry strives to maximize production in US shale plays, the number of extended-reach horizontal wells being drilled continues to increase in efforts to optimize reservoir contact and increase fracture intensity. Because operators demand the same level of performance achieved on shallower wells while providing a cost-effective and safe solution, these wells present complex challenges for completion and intervention operations. Coiled tubing (CT) enables an efficient means to deploy tools and perform pumping operations, such as drilling out plugs, wellbore solids cleanout, and matrix or fracture stimulation in a continuous manner. In any well-intervention operation, the CT size is maximized to achieve the desired level of operational efficiency and effectiveness. To reach the target depth of these extended-reach wells, smaller CT must be used because reel capacity is limited. This not only limits the pump rate that can be achieved, but smaller CT is more susceptible to helical lockup and could require costly assistance to achieve depth. Also, many roadway authorities have established size and weight restrictions that can dictate the size of CT used. A new hybrid solution is now being used to combine the benefits of both CT and jointed tubing (JT) in a single work string. The solution presents many cost benefits while extending the depth of reach that can be accomplished to perform continuous-pumping operations using the optimum diameter tubing and pipe. The system incorporates unique well-control tools that enable seamless functioning of the string in a live well, thus providing considerable time and cost savings. This paper presents the benefits of the hybrid unit and discusses the enabling technology while providing an overview of field trials of multizone stimulation treatments in the Bakken and Marcellus reservoirs.
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