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.

No abstract

The coiled-tubing (CT) industry has evolved from using smaller pipes with lower-grade materials to bigger pipes and high- strength materials. However, the offshore installations and equipment still need to catch up with increased weight and handling demands. A tapered outer-diameter (TOD) string is one solution that provides the benefits of larger string while keeping size and weight at manageable levels. This paper presents a study and analysis of using a spoolable connector (SC) to join strings of two different outer diameters (ODs). A TOD string requires an 8- or 10-ft long “transition section” so that the string can pass through specially retrofitted injectors. The transition section is milled, from one diameter size to another, using a cold-working process. This transition section needs to be welded to the two strings and requires a manual butt weld. As an alternative, a transitional spoolable connector is being developed and virtually tested using finite element analysis (FEA), thus eliminating the need for a specially milled, butt-welded transition section. One challenge with TOD-connection systems is that they tend to fail at the butt-weld between transition and core end of string. A 10-ft long SC was designed to transfer this high-strain area away from the transition where it would be less detrimental to fatigue life. SCs for regular pipes have been designed and tested in variety of sizes from 1.5- to 2.875-in. OD CT. The test data provided a base to compare the performance of this new transitional connector. Results from a 2- to 1.75-in. tapered OD string are presented. One complete bending event of a 20-ft long assembly was simulated on a drum using FEA, and results were compared with actual and virtual test data from pipe with SC and a TOD string with transition section.

As things progress each year in the oil industry, there is a much greater emphasis on safety. Live well-intervention operations are challenging because of inherent risks and require detailed risk analysis and appropriate mitigation, such as redundant safety devices. This paper presents details of the development, testing, and successful field deployment of a newly designed safety valve that can be used on coiled tubing (CT), jointed tubing (JT), and CT-JT hybrid string applications. This safety valve, located at the junction of the CT and JT, is a key component of the CT-JT hybrid string. Once the CT is connected to the JT, the valve can be pressure actuated to close or open the flow path to the wellbore. This allows the hybrid string to be run in hole (RIH) and pulled out of hole (POOH) with complete wellbore-pressure control. Various methods can be used to activate the valve, such as using surface hand pumps, pressuring between blowout preventers (BOPs), or remotely with pressure differential downhole. Double-flapper check valves have typically been part of a standard well-intervention bottomhole assembly (BHA). However, integrity of these valves is always in question after heavy pumping operations, especially with sand-laden fluids. This new safety valve incorporates a protective sleeve that keeps the flapper assembly covered and in pristine condition in its normally open position, helping to ensure a more reliable seal on closure. Chemical compatibility of elastomers, along with low- and high-pressure sealing reliability, are some of the challenges involved with conventional designs. Considering these limitations, the new safety valve offers a true metal-to-metal, non-elastomeric, spherical-to-spherical, flapper-closure mechanism with low- and high-pressure sealing capability based on ISO 10432/API 14A specifications. The flapper valve is designed and manufactured based on award-winning subsurface safety-valve technology. The safety valve was virtually tested using computational fluid dynamics, followed by functional testing on a full-scale prototype. Validation testing for functional, pressure, and sealing capabilities was conducted at an API type test facility. The safety valve was subsequently deployed and successfully passed field-trial operations.

Due to limited crane capability, some coiled tubing (CT) strings are transported in two or three sections to offshore locations, requiring the use of welding or mechanical connectors for reassembly. CT utilization subsequently can be hampered by welding issues as well as lack of integrity of the connectors. Field welding techniques and commercially available spoolable connectors can decrease the fatigue life of CT string to 35-70% of the base tube. This paper describes the development of a mechanical spoolable connector with a fatigue life as good as that of the base pipe. The connector was designed using extensive nonlinear finite element analysis (FEA) design iterations. The connector pressure rating is equal to that of the pipe, and the connector maintains its sealing ability throughout the fatigue life of the pipe—even on very aggressive radius drums and tubing guides. The connector conforms very well when spooled to the drum without "sticking out." The connector assembly OD fits flush with the CT string, providing continuous gripper engagement. Single or multiple connectors can be used to join sections of coiled tubing in the yard or on location. The new connector uses material certified for sour wells and acid jobs, and its seals are compatible with a variety of chemicals, acids, and sour service conditions. In addition, the testing of the connector is discussed. The connector design performed very well according to several prototype tests on a fatigue machine and full-scale yard test. The results demonstrate that the new spoolable connector can increase the utilization of CT with various configurations and enable operations previously not deemed feasible due to various limitations imposed by other joining techniques. Introduction As the offshore industry has moved to accessing deeper reserves, the coiled tubing (CT) work strings required for intervention operations have become longer and heavier. By far, the largest and heaviest component of a CT unit is the coiled tubing itself and the reel on which it is handled. Often, due to the weight of a CT reel and the inability of a crane or other device on the offshore location to lift it, the CT must be placed on multiple reels before being transported to the job. Because coiled tubing work is based on a continuous string of tubing, the CT work string must be assembled before the job is initiated. For onshore jobs, the weight of the CT reel usually is not a significant problem since cranes able to handle single high-capacity reels are typically available. Offshore, weight handling presents a bigger challenge as many platforms are not designed to lift the heavy CT reels off the workboats and onto the platform. Once the coiled tubing is delivered to the platform on multiple reels, another major challenge is joining the CT sections together into a continuous string. Until recently, the preferred method has been to connect the CT sections by butt-welding the ends of the CT; however, this can be an expensive and time-consuming proposition. First, welding specialists are required to set up the operation and, in most situations, a special work permit is required and a discrete area on the rig must be used. Second, in many instances the well(s) must be shut in for the duration of the welding job for safety reasons. Finally, the welds have to be X-rayed by other specialists with more equipment. Ideally, a mechanical, spoolable connector should have the same fatigue life as the base tubing, while maintaining mechanical strength similar to that of the base tubing. The best results published thus far in fatigue life tests are 50 to 60% of the base tubing (Luft, Laun, and Thov 2004). This paper discusses the design and testing of a novel mechanical spoolable connector having a fatigue life equal to that of the base tubing.