Horizontal Reservoir Value Increased by Enhanced Geological Knowledge
Horizontal wells can offer unforeseen reservoir complexity. Although well characterized by surrounding legacy wells, bed dip and thickness may vary in unexpected ways. These variations can yield heterogeneous geomechanical and poro-perm properties in a single well. These may be barriers to fracture propagation or effective rock volume stimulation during completion. In this project, geosteering services were not routinely employed because a well-defined understanding of the reservoir had already been established. Regional and local dip were well known and the impact on drilling, evaluation, and production had mostly been consistent. Execution issues became apparent in the drilling of a horizontal well drilled between two legacy vertical fields. Midway through the lateral, the gas and cutting shows diminished abruptly. Mud log data indicated that the pre-drill structural interpretation was in error and that the lateral had drilled up section back into tighter top seal rock. Attempts to change bit inclination were successful but did little to migrate the wellbore into productive portions of the reservoir. Gas and cutting shows were never recovered. Upon completion, over half of the lateral length was ultimately abandoned due to excessive water production and low oil cut. Fortunately, the operator had collected LWD gamma ray (GR) data while drilling, so post-drill re-steering was applied to the available information. After several iterations, a geologically complex model was derived that matched all the available drilling and mud log information and fit actual production results. Re-steering added valuable knowledge to reservoir characterization efforts and illustrated the variable nature of localized structure and reservoir quality that could not be resolved sufficiently from offset well data alone. A key insight was the need to have sufficient geological description processes in real-time. Geosteering was added on all subsequent wells as a critical geotechnical assessment component. Real-time geological description of the reservoir assisted in keeping wellbores in the most productive portions of the pay zone. As a result, well performance (initial production rates and estimated ultimate recoveries) improved dramatically, and the company’s production has increased by over 400%.
AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019