Geomechanics in Unconventional Reservoir: A New Approach to Drilling Integrating Advanced Acoustic Measurements and Formation Evaluation

Abstract

Abstract The Spraberry Trend oil field produces from a single enormous sand interbedded with shales, and typically pinch-out up dip. Being deposited in submarine channel systems and their associated fans, the sands are with very low porosity and permeability, both of which impede oil recovery. Oil has accumulated in stratigraphic traps, migrating upward from source rocks until find impermeable barriers. However, the natural fractures further complicated the hydrocarbon flow and pose drilling challenges in this field. A client has planned to drill deviated wells in Spraberry Trend area. They aimed to drill the wells with less drilling issues and Non-Productive Time. Wellbore instabilities and mud losses are more than in all wells drilled in Permian Basin and more specific in the prolific and acclaimed Midland Basin. Those drilling events are crucial to defining if the well will reach the goals and plans developed by geoscientists, drillers, and petroleum engineers. Decisions like casing points, open hole intervals, kick-off-points, curve sections, and finally landing points are very impacted if wellbore instabilities are present and this management is difficult to mitigate. To boost the drilling campaign, it was important to take control of the borehole problems and it was achieving through mud weight optimization. The laminated reservoir showed that isotropic stress model would not give correct stress parameters. Thus, a new workflow is being inherited to cogitate TIV (transverse isotropy vertical) stress model for wellbore stability analysis. TIV anisotropy analysis was performed on a representative vertical well using advanced acoustic measurements and the model was calibrated with post-drill events. This calibrated model gives the stable mud weight window for four planned laterals. This paper will highlight how a geomechanics-based approach, integrating advanced acoustic measurements, has significantly improved drilling rates by reducing drilling-related problems. The wells were drilled keeping the mud weight at the lower limit of the stable mud weight window. This led to faster drilling with an average rate of 1,300 ft/day. Reduction in wellbore instability issues has led to considerable reduction in time spent on reaming, mud circulation, cleaning tight spots, etc. This effectively reduced Non-Productive-Time and rig cost. Wellbore stability analysis incorporating anisotropic stress from advanced acoustic measurements has helped most right mud weight estimation and thereby drilling the wells at a faster rate in the unconventional reservoirs.