Abstract: Advantages of "Real-time" LWD Dipmeter Data

GRAYSON, STEVE, JIM EZELL, JON SCHWALBACH, DALTON LOCKMAN, and DAVID ROSE

Advances in Logging While Drilling (LWD) technology now make it possible to acquire formation bed dip information while drilling, using Anadrill's RAB (Resistivity At Bit) tool. The use of button resistivity electrodes mounted on a rotating LWD tool provides the data for a resistivity image of the borehole. These images are the basis for ongoing structural interpretation as a well is drilling and can be used to "geosteer" the wellbore to an optimal location.

A well recently drilled in the Santa Ynez Unit of offshore California (U.S.), illustrates an application of this technology. A highly deviated well path (77 degrees from vertical) was designed to intersect a gently dipping (5 degrees) Monterey Formation target. This nearly parallel borehole-strata geometry provides little room for error when attempting to intersect reservoir intervals at specific elevations. In this case, the RAB data collected and processed at each bit trip indicated that formation dips were actually 10 degrees instead of 5 degrees as anticipated in the original well plan. If drilling continued along the planned well path, the reservoir interval would not be intersected at the target elevation. In response to the RAB dip information, the well angle was decreased to encounter the reservoir zone within the oil column, resulting in a successful completion.

Other applications of the RAB data include precise location of faults and structural culminations, and in some cases the identification of highly fractured intervals. When integrated with other LWD data, and mud logs, well paths can be directed as drilling progresses, avoiding costly sidetracks and redrills.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria