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