Geologic Interpretation and Engineering Classification of Rocks Improves the Drilling Performance in New Mexico

By

Ashok Bhatnagar, RBI-Gearhart, and Simianne J. Hayden, BEPCO

 RBI-Gearhart utilizes a stochastic modeling based software application for generating geologic interpretations, calculating rock strength properties to select optimum drill bit types.  Interpretations from the application have significantly reduced drilling times and costs on multiple wells drilled in New Mexico.  Data from offset wells were analyzed with stochastic modeling, based upon weighted least square error minimization, to derive the physical properties of the rocks.  Since the logging suite from the offset wells did not include a Sonic log needed for computing the elastic properties and velocity ratios; the stochastic model was used to derive computationally the compressional and shear wave velocities.  After calculating the dynamic elastic properties and deriving the compressive strength, engineering classification of the rocks was done to optimize the drill bit selection. Based on the interpretation and bit proposal, three wells were drilled by the operator using PDC bits for the first time in this geological environment of anhydrite, halite, sylvite, sand, clay, silt and limestone.  The drilling time on the first well was reduced by 27% and with the new information gained, special drill bits were designed for the second and the third wells. The third well was completed with just two drill bits, compared with four earlier, to further cut the drilling time by 43.5%, a new record in the area. Even with significantly faster ROP, the caliper did not indicate any deterioration in the bore hole profile. The success of the project is attributed to the team effort realized between the operator and RBI-Gearhart.

AAPG Search and Discovery Article #90010©2003 AAPG Southwest Section Meeting, Fort Worth, Texas, March 1-4, 2003