Drilling the intermediate section of deep gas wells in a Middle East field is quite challenging due to geological and wellbore instability problems, and the associated risks such as total losses, twist-off, stuck pipe, and casing not reaching bottom. Casing-While-Drilling (CWD) combined with stage-cementing tool with inflatable external packer has been implemented in a 16″ intermediate section to prove the viability of the technology in such downhole conditions, and moreover, improve the operational economics of drilling this section with conventional drilling.

Whereas CWD is a proven drilling technology worldwide and deployed across the field at shallower depths or smaller sizes, a proof-of-concept implementation would be needed in a deep gas well to establish the limits for the technology while drilling in a big hole size (16″) to a deep casing point (~5,000 ft). An extensive case study for the application of CWD was conducted, which covered the main technical concerns: torque while drilling, casing fatigue, drilling fluid strategy, float equipment and stage-cementing tool reliability, expected rate-of-penetration and bit design, drilling parameters road map, and contingencies.

CWD level 2 technology was successfully implemented in the gas field for the first time. The technology had proven its viability in a deep big hole size by drilling approximately 500 ft in the above problematic section, and across the more challenging formations to a total depth of 6,501 ft. The section was drilled with 70 hours of on-bottom drilling and a total of 88.25 hours of tripping and circulation. A new benchmark was established for the reliability of float equipment and stage collar with constant rotation as reaching the total depth of a challenging drilling environment. Plastering effect also proved its liability as no losses was observed despite the high risk from offset wells. Additionally, no losses were induced in case of full circulation scenario, and cementing operations completed successfully with no losses. Low vibrations, and smooth torque observed while drilling. The main advantages of this implementation in gas wells are mitigating the potential risk of wellbore instability related to lost circulation, minimizing potential twist-off and stuck pipe events, and reducing the hole exposure time due to excessive reaming while tripping. Shale reaction and hole bridging in the formation can be avoided since no tripping is required.

CWD has been proved as a feasible technology for challenging intermediate sections in gas wells. Further developing the technology in the field for risk mitigations and optimizing the operational economics are ongoing, such as introduction of new CWD PDC bit and performance improvement from identified lessons identified. This manuscript will share the developing strategy behind proof-of-concept and technology evolution and will serve as a reference for service companies and operators in the region in similar cases.

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