The field development plan for a Sarawak Shell Berhadoperated gas field, located in the South China Sea, offshoreSarawak, Malaysia, specified drilling of horizontal wells intothe Tertiary Miocene Carbonate reservoir. The wells wereplanned as high capacity producers of the Big Bore-LongCasing Flow design.The traditional well design dictated that, prior to enteringthe reservoir, a casing had to be installed to stabilise the holein soft shale. The uncertainty of detecting the formation topresulted in premature casing commitment of at least 30 feetTVD above the top of the reservoir and the need to use anexpandable liner to cover 300 feet of exposed shale abovethe reservoir.To obviate this problem, the capability of one of thecomponents in the Logging-While-Drilling tool array, namelythe Electromagnetic Wave Resistivity forward modelingtechnique, was used to detect the top of the carbonateformation (top reservoir), immediately prior to drilling into it.A standard Logging-While-Drilling tool is configured toprioritize Electromagnetic Wave Resistivity forward modelresponse as the carbonate formation top is approached. Thisconfiguration, together with an appropriately designed bottomhole-assembly and well trajectory, enabled the successfulimplementation of the plan to stop drilling approximately onefoot true-vertical-depth above the carbonate top.At this point, a conventional 9 5/8-in. casing string was setat an optimum depth. This eliminated potential well controlproblems, costly remedial actions associated with lostcirculation and inferior cementation of the 9 5/8-in.casing string.Thereafter, the wells were drilled horizontally in aconventional manner, into the carbonate gas reservoir.This paper compares pre-drilling Electromagnetic WaveResistivity forward modeling of the proposed well trajectorywith the actual well data, whilst drilling. The pre-drilling andpost-drilling modeled data is presented.The cost savings from employing this technique arevariable, ranging from substantial - in the event of a wellcontrol situation and attendant high losses - to moderate if theneed to set an expandable is eliminated.
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