Abstract

Krishna Godavari Offshore Block has reservoir temperatures of 420 degF and 12,500 psi of bottom hole pressures, field's HPHT rating is a concern moreover other challenges like the wells are complex in terms of depths, profile, high drift, reservoir with heterogeneity, formation pressure variation. The paper discusses challenges during well planning and their execution with adequate methods to successfully drill and case well with less than 15 % NPT.

In harsh environment of KG Basin, HPHT wells encroach on limits of equipment, leaving little margin for error, resulting in increased risk of rapid gas migration, equipment integrity failure, operating limits of tool. The paper discusses use of RSS-Vortex, 200 degC rated MWD tools, NRDPP, modified casing design, reduction in impact of side forces and high torques, optimized bit design, drill pipe cutting tool, reduction of differential sticking to execute the drilling of well within given time. The case study discusses longest 5 7/8" section drilled in an unconventional casing design under HPHT environment in India.

The paper also discusses the unexpected results and observations obtained during execution of program and the lessons learnt from it. Some drilling methods such as first application of RSS-Vortex in a HPHT environment in India has considerably enhanced the ROP by 100% and also significantly reduced casing wear of production casing by 55 %, use of 200 deg C rated MWD tools has increased the robustness of the drilling BHA resulting in minimizing additional BHA trips due to tool failures. The reservoir section drilling has been optimized to 3 bit trips from 9-13 trips done in offset wells. Use of NRDPP's made drilling of high drifted wells easier and maintenance of surface torque within limits had considerably reduced lost production time and ensured safe operation. The improvisation carried out for bit design and casing design has also saved rig days and cost. The new casing design avoids liner tie back which has resulted saving of 7 days of rig time. The use of effective micronized barite OBM system with controlled measures on HTHP fluid loss has maintained good balance between rheology and fluid loss to prevent differential sticking. The downhole tool failure and stick-slip was reduced by 50% by modulating the Variable frequency drive and choosing adequate bit.

These methods and practices require further optimization to enhance the usability. The established methods discussed have created good drilling practices in HPHT environment for KG field and has reduced the drilling NPT levels. Such a huge transformation in reducing the NPT is very significant in HPHT conditions and many of the practices can be standardized for such operations.

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