How to Manage CT Operations in Hostile Environment: Field Case Studies on CT Challenges in Deep HPHT High Sour Carbonate Formations

Objective of this paper is to present our recent case-histories involving uncommon and unexpected Coiled Tubing (CT) intervention challenges in exploratory wells while testing and stimulating deep HPHT high Sour carbonate formations. Jurassic formations at around 17,000 feet in Kuwait are tested using cased-hole Drill Stem Testing (DST) system. 15K CT is employed during DST for displacement of kill fluids to achieve under balance prior to perforation, placement of acid for stimulation and for well killing operations. CT operational challenges encountered during testing deep exploratory wells are high pressure reservoir(>10,000 psi), limit on CT injection pressure>10,000 psi, pumping acid of 28% HCL, sour well fluid, salt plugging, etc. Well intervention under such challenging conditions requires proper planning, right equipment, techniques and procedures to ensure safe operation. Existing challenging conditions were well managed and objectives were met. A new problem of formation solids production after acidization of Kerogen rich carbonate/shale formation created a new challenge for CT operations which is unlike the common problem of sand production from the unconsolidated sand stone formation. In some wells, DST string got plugged with solids after acid stimulation and obstruction/stuck-up was encountered while operating CT. Another unexpected problem is the high H2S concentration of 35% in the recently discovered field. The unexpected challenges created unwarranted situation. It is a challenging task for operators to execute the safe and successful CT operations under these uncommon and unexpected conditions. Initially, even some of the service companies expressed their inability to operate CT under these extreme conditions. The unexpected problems are managed well within the available resources and the well test operations were executed safely and successfully. The new solids production operational experience has helped the operator to avoid the reoccurrence of CT stuck up thereby decrease the operational risk and increase the success rate. It has been proved practically in the field that CT can safely be utilized in high sour wells up to 35% H2S and increased the operator confidence. The experience gained, new challenges encountered, safe practices followed and way forward for execution of successful coiled tubing intervention in hostile environment will be discussed in this paper.