Abstract

Pressurised Mud Cap Drilling (PMCD) is a variation of Managed Pressure Drilling (MPD), that involves drilling with no returns to surface and where an annular fluid column, assisted by surface pressure, is maintained above a formation that is capable of accepting fluid and cuttings. The application of this technology in drilling fractured reservoirs has been long established. However, formation evaluation techniques in such reservoirs are yet to be established due to the challenges that are associated with wireline logging in such a drilling environment.

Concerns related to total loss circulation, potential gas migration, and unsustainable fluid logistics have led to the perception that wireline logging operations during PMCD are impossible or logistically impractical. Apart from that, there are also concerns with regards to data quality due to the uncertainty of borehole conditions. Conveying wireline tools via drill pipe is also ruled out as the Rotating Control Device (RCD) sealing elements are not able to seal on wireline which is outside the drill pipe in Drill Pipe Conveyed logging system.

This work focuses on a new development that allows wireline logging under activated PMCD condition in wells drilled through carbonate gas reservoirs. The main challenges in evaluating such reservoirs are obtaining representative reservoir fluid samples and identifying fluid contacts needed for reserves booking. This paper will present the new developments and procedures on both operational and technical aspects. Field data and work flow will be used to demonstrate how the new development enabled the successful evaluation of fractured Pinnacle Reef carbonate reservoirs under total loss circulation and PMCD activation.

This paper discusses the operational details on wireline logging with activated PMCD, challenges encountered due to borehole conditions as well as acquisition results, lessons learnt, recommendations and conclusions.

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