Kuwait has been drilling and producing from the deep, sour Jurassic reservoirs during the past 30 years. Drilling high angle wells / horizontal wells can provide a means to intersect possible oil bearing fractures besides extending the drain hole length for increasing productivity. The wells drilled to these prospects are challenging because of HPHT conditions, narrow mud weight window and sour gas. The Jurassic reservoirs itself exists below a deep high pressure formation G bearing multi Salt-Anhydrite sequences. The Jurassic wells are typically based on big bore well design with the final hole size ending in 6 ½"/6" hole size. The well constructions typically comprise of seven casing policy and requires 15 K well control equipment. It is imperative that surface/intermediate casing strings are run to the maximum depths possible in order to reach well TD in the planned workable hole size. The isolation of formation G with the planned 10 ¾″ casing is essential to drill and complete the wells efficiently. In well A-14, due to complex geology, the required formation top could not be ascertained. The well construction was altered to case off the unexpected recurrent high pressure section which led to downsizing of the available hole sizes to drill upper and lower Jurassic reservoirs in slim hole. As the planned horizontal of required length was deemed infeasible in 4 ½" hole size, the well was converted to an high angle well. The unusual presence of fracture corridor with high pressure hydrocarbons below formation G posed a series of challenges. The drilling window was extremely narrow between 18.4-18.6 ppg where drilling had to be continued either with ECD or under losses with high density fluid of 18.5 ppg. The requirement to achieve the well profile with known limitation of directional drilling tools to use LCM pills was planned with due controls. On many occasions, the removal of ECD resulted in gains and many well control operations had to be resorted to including bull heading during trips. The well was drilled to TD and the upper Jurassic reservoir tested successfully. The paper will present lessons learnt, practices employed to drill with losses and gains, tripping considerations, fishing complications, slim hole drilling challenges, improvisation of drilling and cementing practices in near total loss situation and directional drilling techniques adopted. This would then provide the basis for future optimization in these types of wells.
This paper highlights the design, planning, challenges, operational complications and successful execution of coil tubing application in active deep well in West Kuwait. The aim of coil tubing job is to clear the pipe from inside to recover the stuck pipe to eliminate the sidetrack in highly pressurized complicated Salt/Anhydrite sequence. In one of the West Kuwait wells, during drilling the well got a kick with high gain rate. During shutting in and at starting of killing the well, it was observed that the pipe & annulus were plugged. Pipe puncture job was carried out & the well was killed off bottom with 19.7 ppg mud. Throughout running in hole with the free point locator tool prior to back off job, the held up was observed at 12,490 ft i.e. 1,300 ft above the bit. It was then selected to clean inside drill pipe to avoid sidetracking. The well conditions presented challenges to the design and operation of coil tubing in this well. Challenging factors included: Use of high weight and yield strength, 15 ksi coil tubing, high mud density of 19.7 ppg, high pumping pressures, deep well, ID restriction 3 ½ in DP with 2 in ID, active well, deviated well of around 57 degrees. The coil tubing job design was critical for success of the operation. It included selection and analysis of coil tubing material, size, wall thickness; managing potential coil tubing burst and collapse pressures, calculation of coil tubing stretch, circulation pressure with high density mud, coil tubing force analysis, and wellbore solids removal with very minimum clearance & minimum pumping rate. Initial simulations with 1.5 in coil tubing showed that circulation pressures would go above the 15 ksi rating. It was then decided to switch to high pressure 1.75 in coil tubing with which simulation showed that pressures at the rotating joint would be at 8,000 psi, using a jetting nozzle. While lowering with jetting nozzle, held up was observed at overshot due to the deviation. After changing jetting nozzle with the 1 11/16 in kick off tool, the coil tubing was able to pass through the gelled mud with circulation. To keep under check, high circulating pressure with aid of hydraulics analysis, related to dynamic circulation rate to 0.2 bpm at 7,500 psi & static rate to 0.35 bpm with 8,500 psi. Resulting in successfully clearing the drill pipe from inside to 12,974 ft, below the observed settling of hard barite. Coil Tubing intervention with the restricted pipe diameter and heavy mud at high inclination well using a kick off tool was done for the first time in Kuwait. It achieved the purpose of cleaning the pipe to definite depth enabling back off operation below the jar & enhanced the chance of pipe recovery.
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