The field development plan for a Sarawak Shell Berhad operated gas field, located in the South China Sea, offshore Sarawak, Malaysia, specified drilling of horizontal wells into the Tertiary Miocene Carbonate reservoir. The wells were planned as high capacity producers of the Big Bore-Long Casing Flow design.

The traditional well design dictated that, prior to entering the reservoir, a casing had to be installed to stabilise the hole in soft shale. The uncertainty of detecting the formation top resulted in premature casing commitment of at least 30 feet TVD above the top of the reservoir and the need to use an expandable liner to cover 300 feet of exposed shale above the reservoir.

To obviate this problem, the capability of one of the components in the Logging-While-Drilling tool array, namely the Electromagnetic Wave Resistivity forward modeling technique, was used to detect the top of the carbonate formation (top reservoir), immediately prior to drilling into it. A standard Logging-While-Drilling tool is configured to prioritize Electromagnetic Wave Resistivity forward model response as the carbonate formation top is approached. This configuration, together with an appropriately designed bottom-hole-assembly and well trajectory, enabled the successful implementation of the plan to stop drilling approximately one foot true-vertical-depth above the carbonate top.

At this point, a conventional 9 5/8-in. casing string was set at an optimum depth. This eliminated potential well control problems, costly remedial actions associated with lost circulation and inferior cementation of the 9 5/8-in. casing string.

Thereafter, the wells were drilled horizontally in a conventional manner, into the carbonate gas reservoir.

This paper compares pre-drilling Electromagnetic Wave Resistivity forward modeling of the proposed well trajectory with the actual well data, whilst drilling. The pre-drilling and post-drilling modeled data is presented.

The cost savings from employing this technique are variable, ranging from substantial - in the event of a well control situation and attendant high losses - to moderate if the need to set an expandable is eliminated.

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