Abstract Drilling technology advances have extended the reach of well depths and complicated trajectories which have in turn created challenges for rig-less well intervention around the world.Extended reach horizontal wells up to 25,000 ft deep require that coiled tubing designs be carefully analyzed to determine when weight stacking and lock-up will prevent coiled tubing from reaching the desired total depth.If the well requires stimulation, then the benefit of coiled tubing is its enhanced placement capability to uniformly inject a treatment across a desired interval.An effective treatment diverting method can further improve these results, especially when coiled tubing is not able to access the entire pay interval.When coiled tubing locks-up before reaching the total depth for one of these treatments, a decision must be made to bullhead the treatment into the lower unreachable section, hoping for uniform placement, or to employ technology which can extend the reach. Larger diameter coiled tubing, coil tractors, liquid friction reducer, mechanical vibrational friction reduction, and buoyancy effects are techniques which can extend the reach of coiled tubing.
Sensitivity analysis was run for the aforementioned techniques and a new vibrational tool combined with a liquid friction reducer on 2-inch coiled tubing was chosen to successfully acid stimulate a horizontal open hole well.This configuration allowed the coiled tubing to reach 25 percent further than the initial lock-up point and the combination of this technique with a new viscoelastic surfactant diverting system, successfully treated the damaged well for a gain of 6,000 BOPD.
This paper will review the stimulation design process and three innovative technologies which have been combined with coiled tubing to successfully treat extended reach wells in Saudi Arabia. Introduction Directional drilling technology, reliability and capabilities have enabled drillers to place a well path with amazing accuracy, which in turn has created an extensive number of well configurations and complexities around the world. Horizontal and multilateral wells have become common place and many mature vertical wells have become candidates for sidetrack horizontal recompletions.
Horizontal wells have more reservoir contact area than vertical wells and productivity index ratios should be much larger, but like a vertical well, the impact of skin effect on the production rate can be large. This concept is especially important, when considering the significant contact time a drilling mud has with the formation when drilling openhole sections of up to 12,000 ft.
Drill-in fluids can cause formation damage as a result of mud filtrate and particle invasion into the formation.Assuming mud filtrate compatibility with the formation and that the correct bridging material has been correctly sized to the formation's porosity, then the majority of mud related invasion damage is generally limited to the near wellbore region and should reflect the longer exposure moving up the well from the toe to heal section.
Skin damage in these wells often necessitates an acid wash to remove the drilling induced skin damage.It would be desirable to perform the acid job while the rig is still on location, but the effective treatment of a long horizontal section requires careful design and operational consideration.
The choice of treatment fluids is made based on damage remediation effectiveness, formation compatibility, safety and cost.Safety and rig cost are probably the primary reason a clean up treatments is not performed by the rig. It would be ideal to spot a cleanup treatment while pulling the drill pipe out of hole, but conventional hydrochloric acid treatments are too reactive to safely allow for drill pipe to trip out of hole before well control becomes an issue.Enzyme technology is successfully being applied this way,[1,2] but buffering reaction rates for long sections is still a challenge.[3]