Casing Drilling was introduced to optimize the drilling of the top hole section in the Phase 1 wells of the mature Samarang Field re-development campaign. Lost circulation and stuck casing incidents in the surface section had been observed in previous campaigns, and Casing Drilling was identified as a solution to mitigate these problems.

Company procedures require that a pilot hole be drilled on the first hole section out of the conductor on the first well drilled during a platform revisit, for shallow gas mitigation. Although the risk of shallow gas was considered low in the Samarang field, the requirement applied to the first well to be drilled in the campaign. In the absence of a conclusive shallow seismic survey, other analyses to evaluate the likelihood of shallow gas were used, and Casing Drilling provided a different approach to mitigating the risk of shallow gas blowout.

This paper discusses the benefits of Casing Drilling in Samarang, with special focus on its application as mitigation for a reduced risk of shallow gas blowout. It reviews the modeling and risk analysis conducted to justify and obtain the waiver required to drill without drilling the conventional pilot hole. It also discusses the lessons learned from the execution.

The implementation of Casing Drilling in mitigating the shallow gas drilling risk, among other benefits, was a significant milestone in the project. The drilling operations became more efficient based on the substitution of the pilot hole on the first well of the re-development campaign. This has opened the opportunity for potentially valuable savings in the next phase of the project (with seven platform revisits) and other similar brown fields revisit campaigns.

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