TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMany of the producing fields in the Cook Inlet area of Alaska are found in tightly folded, asymmetric, fault bounded, anticlinal structures that are not easily imaged with modern seismic. Historically, exploration wells have been drilled initially on the crest of these features, only to find at total depth that the bore holes had deviated off the crest and were several thousand feet down dip from the initial structural objective.In Cook Inlet, where difficult hole conditions prevail, a new approach to real time structural analysis was needed to evaluate complexly folded features as they were being drilled.Acquisition of structural dips while drilling a potentially complex structure was critical in evaluating the position of the well on the structure and steering it if necessary. Measurement while drilling (MWD), coupled with logging while drilling (LWD) provided the data necessary to enable a successful drilling operation and well completion.The Resistivity-at-the-Bit (RAB)* tool was used during drilling to acquire resistivity measurements close to the bit. These resistivity measurements were then used to produce images and calculate dips similar to a Fullbore Formation MicroImager (FMI)*. Modifications to the structural model were continually made based on interpretations from the RAB images, allowing the bore hole to be steered towards a preferred structural position.FMI and RAB images and interpreted dips were compared in a shallow interval to evaluate the quality of RAB data. Excellent agreement in measurements between the tools resulted in the continued use of RAB for the duration of the well.

This paper was prepared for presentation at the 1999 SPE Rocky Mountain Regional Meeting held in Gillette, Wyoming, May 15–18.