Recent advances in horizontal drilling technology have allowed drilling longer horizontal sections in the reservoir more efficiently and economically. While operators benefit from the well-known advantages of horizontal drains, such benefits cannot be maximized during the lifetime of the well without a viable well intervention means for well service and monitoring operations. Coiled tubing has been recognized as an effective technique for such interventions but with limitation on the total length that can be accessed especially in extended reach wells. This paper summarizes the utilization of innovative coiled tubing Tractor technology to improve coiled tubing accessibility in long horizontal wells .
The paper discusses the aspects of well intervention using coiled tubing (CT) and coiled tubing tractor technology on four (4) open hole horizontal water injection wells and one (1) cased hole oil producing well. The results presented show that the use of a coiled tubing Well Tractor combined with coiled tubing along with proper well selection, design and planning can result in a significant improvement in Well accessibility both in cased hole and open hole .
For a well to be accessible with coiled tubing, the coiled tubing need to be run to the end of the horizontal section and no "lock-up" should happen before reaching TD. Lock-up occurs when no weight can be transmitted to the end of a coiled tubing and hence no progress into the horizontal section is possible. Coiled Tubing simulation software is available that can predict the depth at which this lockup is reached and whether it will occur. Such simulations are often used in the planning stage of a coiled tubing Intervention to decide on the type of coiled tubing pipe to be used (diameter and thickness). The following factors are taken into account in the simulation : Well trajectory, coiled tubing pipe variables (OD, thickness, strength, length), Diameter (s) in the wellbore, friction coefficients (cased/openhole), Well fluid type, temperature, pressure, and wellhead flowing conditions. Many techniques can enhance coiled tubing accessibility into the wellbore : The use of larger pipe, pipe straighteners, vibrating tools, pumping of Nitrogen, pumping of friction reducers or a combination of the above. A lot of literature has been published and is available about these techniques. Figure (1) shows coiled tubing Lockup depth using a typical output of a Well Intervention simulation program [refer to point A on the graph]. This is the "theoretical" Lockup point. Actual Lockup point can only be found when the coiled tubing is run into the hole.
The advantage of using a coiled tubing Tractor at the end of coiled tubing is that it provides a concentrated downhole force that can delay or prevent lockup by "pulling "the coiled tubing from its end. This often results in improving well accessibility on extended reach wells. It is thought that when the CT locks up, a spiral type of form takes place at the end of the coiled tubing section; having a concentrated point load acting at the end of the coiled tubing will make this event unlikely thus improve the accessibility. Figure (1) shows the new lockup depth predicted by the well intervention Simulation program [refer to point B on the graph] after applying a concentrated force of 4000 lbs by the Tractor at the end of the coiled tubing as per the well intervention simulation.