Karachaganak Petroleum Operating b.v. (KPO), the operator of the giant Karachaganak gas-condensate field in Kazakhstan, drills long horizontal wells and then stimulates them with acid. A variety of acid stimulation techniques have been used, progressing from simple acid washes to high-rate matrix acid treatments and hydraulic fracturing with gelled acid. KPO performed a sidetrack workover operation on a vertical well JH16D due to low productivity. The vertical wellbore was abandoned, side-tracked and completed with 4 ½-in liner and 1186 m of 6-in openhole (OH) horizontal length. To run the completion safely, one composite bridge plug (CBP) was set in the vertical section at 4850 m. To put the well back on production with a rigless operation, a coiled tubing (CT) job was planned to perform CBP milling, oil-based mud (OBM) removal, solvent soak and acid treatment along the entire OH section
In this paper, the predicted challenges during pre-job modelling for reaching total depth (TD) of 6492 m are summarized. Based on the current CT equipment and string available in the country, the only solution to reach TD and effectively enhance fluid placement along OH was accomplished by adding a fluid hammer tool (FHT) as part of the CT bottomhole assembly (BHA). FHTs are used in CT jobs for extended-reach applications by generating a temporary tensile load and lowering of the coefficient of friction (CoF) between the CT and the well.
After completing CBP milling in the vertical section without using the FHT, two runs were performed with this technology. The first run was a milling run to push the remaining CBP debris to the end of the OH section. During this trip 6382 m was reached; 148 m more compared with the previous run without using the FHT. The next run was performed with the conventional jetting BHA and TD was reached five times during the OBM removal, solvent soak and acid treatment operation. After being inside the well for 110 hours and several fluids such as slick brine, mud softner, solvent, and 15% hydrochloric acid (HCl) were pumped, the FHT proved to be reliable in extending reach to TD in the 6-in OH horizontal section, even under aggressive downhole conditions.
Additional post-job analysis of test runs comparing surface weights with the FHT operating and switched off illustrated that predicted to actual weight changes were accurate.
This successful job opens a new window of applications, in this operating area, such as FHT and downhole motors to mill balls and baffle seats in horizontal completions at deeper target depths than previously achieved. Pre-job predicted and post-job actual tensile forces matched well. This combined BHA gives more weight on bit (WOB) while milling that reduces milling time and also improves maximum reachable depth while milling. In addition, because of the FHT tensile benefit, longer balls and seat baffles completions can be placed in future wells, increasing their production.