Intervention Operations in Long Horizontal and Multilateral Wells Using Coil Tubing

Once the extended reach horizontal and multilateral wells are drilled, the access to perform any intervention in those types of wells is possible with the use of coil tubing most of the time.

?Multilateral Entry Tool

?The demanding conditions of the multiple laterals in terms of geometry and reach make access to this type of well a challenge. For any operator, the goal is to have access to the laterals any time after they have been drilled, allowing them to perform any clean-out, stimulation, or data recording operations. If the access for multiple laterals in a single run is achieved, that reduces considerably the lengthy amount of time to perform an individual intervention and then pull out of the hole to retrieve tools and run new ones, targeting the other laterals. Getting access to all laterals in a single run allows saving in terms of resources and leads to minimizing risks associated with multiple operations. For coil tubing, there is a Multi-lateral entry tool that is activated by pumping a mapping fluid, requiring 12 cycles of 30 degrees each cycle and additional 2 cycles to get access to the lateral. Entering the lateral is confirmed with CCL. Losing the CCL signal and a pressure drop is an indication of successful access to the lateral. In case of access is not achieved, the ML tool is pulled to the surface to perform another function test on the tool. A tool failure is indicated by a pressure change.

The ML tool was deployed using 2 7/8” coil tubing in two different wells in Saudi Arabia, performing different operations. In one well, the goal was to access three laterals and then pump a mud cake removal fluid, in the form of an acid wash to remove any remaining mud cake, after the drilling operations. In this well, The ML tool was run to the first target lateral, L-1-2, and after activating the tool, the access was accomplished in the first cycle. The CT was run to TD, then when POOH, the treatment fluid was pumped. The CT was then pulled targeting the second lateral, L-1-1. After unsuccessful 14-cycle attempts, the ML was then moved to target the L-1 lateral, which was accessed with no problem. The CT was then run to the TD. After this, the CT was pulled to the surface. It was found out the cycling valve from the bottom hole assembly of the CT unit was not working. A new ML tool was used in the new BHA. This time, again the lateral L-1-1 was the target. On this occasion, after 4 cycles, the lateral was finally accessed. After the acid treatment, the CT was pulled to the surface.?

?The goal of the second job was to access tree laterals and perform an acid job on a water injector well. The 2 7/8” coil tubing was RIH to target L-2 lateral. 13 cycles were required to finally get access into the lateral, indicated by a pressure drop. Drag reducer was pumped RIH and 12% HCl acid was pumped while pulling the CT. The second lateral, L-1, was the target subsequently. After 14 cycles, it was not possible to get access to it, so the mother bore, L-0 was stimulated, reaching TD with no problem. L-1 access was tried again, with no success. The CT was pulled to the surface. The ML tool was changed and RIH again. This time, after 8 cycles, the lateral was accessed. The acid was pumped while POOH.?

High Pulse Tool

One way to give support to the CT to reach the target TD of any long lateral is the deployment of a high-frequency tool, which is a “mechanical” drag reducer. The high pulsing effect is activated by a rate increase of the fluid being pumped. In the case of the ML wells using the ML entry tool, once the lateral is accessed, the rate is increased to isolate the ML entry tool and activate the high-pulse agitator which will help reach the TD.

Following there is the data from a?field case, for a horizontal well where this high-frequency tool was deployed.?

Run 1: No high pulse tool.

The CT was RIH only with no agitator. After reaching the 6 1/8” open hole section at 9200 ft. the clean-out was started by increasing the pumping rate. The target TD was at 14,500 ft. Some tagging spots were observed, along the horizontal section, indicated by the high weight fluctuation of up to 25,000 lb. The maximum reach was 10,100 ft. The decision was to POOH and run a new BHA with the agitator. Figure 1, illustrates Run 1.?

Run 2: Second Run Using 2.875” Jetting Nozzle with Agitator.

After adding the agitator to the BHA, the CT was RIH. Once the open hole section was reached, the agitator was activated, and continue RIH to perform the acid stimulation. The weight fluctuation considerably decreased, getting up to 1000 lbs on average. The maximum reached was increased to 12,500 ft. Still, the target planned TD was not achieved, due to limitations with the CT weights and so decreased pumping rate. Figure 2 shows the performance of Run 2.?

As seen, there is a great drag reduction indicated by the slack weight decrease when the agitator is added to the CT BHA. Anyway, drag reducer fluids are also pumped to help decrease the drag effects on those wavy and long horizontal wells.??

Friction coefficients for simulations

?One of the required tools before running a coil tubing in any well is a simulation, considering the conditions of the well, particularly the trajectory and dog leg severity to define the reachability of the CT and the loads during RIH and pulling out.

In extended-reach wells, the common practice is to use a 0.4 fraction coefficient as the maximum value and a 0.3 CH friction coefficient in the case of the majority of the wells. According to Aramco’s CT manual, for wells with unknown friction coefficients, the values are 0.5 for the open hole section and 0.35 for the cased hole. What is the importance of those numbers? The reachability depends entirely on those coefficients. Normally using general numbers, the target depth is most of the time?achieved, according to the simulations. In real life, this is not the case. In the case of the well where the agitator was deployed, the depth reached was around 50% of the expected TD. For the operator, this is a failure case. For the service company, this is a problem related to the unrealistic friction coefficient used in the simulations.

The recommendation in this case then is to use the final reached depth during the CT intervention and back-calculate the friction factor to be used in future well interventions with CT for that specific well, provided most of the conditions remain similar.?So, instead of using recommended numbers in a manual, the coefficients are calculated based on field cases.?

Summary

Once the wells are in operation, routine tasks are carried out to get access to lengthy horizontal and multilateral wells for servicing purposes. Drag forces, however, prevent access to TD in long horizontals in complex trajectories. Much more difficult access is required for multilateral wells. There are already possibilities to use hydraulically activated tools that may be added to coil tubing BHA in order to properly support those activities. This would save time and money while, most importantly, lowering the operational risk associated with an increased number of runs when gaining access to multilateral windows.