In Cairn India’s first ultra HPHT well RX-11, the biggest challenge was the narrow margin between pore and fracture pressures in the deeper HPHT sections of the well. In HPHT wells, high annular frictional losses while pumping causes increase in ECD, thus inducing lost circulation because of narrow pressure margins and, in very severe cases it can even lead to well control events. Such problems were experienced extensively in offset wells and therefore to reduce the annular frictional losses, the use of micronized particle drilling fluid was thought of & introduced in Cairn for RX-11.

Extensive research went into the application aspect of Micronized particle drilling fluid as various simulations & lab tests were done at the time of contract award. HSE risks owing to the suspension tendency of micronized barite in air were identified & mitigated. One big challenge lay in the mixing of mud at rig site as large volumes were required for drilling (due to hole size) and accordingly mud mixing plan was formulated to ensure uninterrupted supply at rig site.

Post all the planning, the micronized particle drilling fluid was used to drill the last three HPHT sections of the well and it proved highly successful in reducing the ECDs as well as providing good hole cleaning (at low flow rates) with minimal maintenance, which enabled drilling to continue through the narrow pressure margin sections of the well. In high temperature conditions, the drilling fluid was found to be stable & undegraded even after 10 days of static condition with no change in hole condition upon re-entry. In addition, caliper log recorded a ‘gun barrel’ 12.1/4″ hole drilled using the same drilling fluid and further it contributed in a near perfect 9.7/8″ casing cementation recorded by CBL-VDL log.

This paper via a case study showcases the concept, project planning & successful implementation of Micronized particle drilling fluid in RX-11 well & makes recommendations for its use in similar projects.

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