The Spraberry Trend area is a pinch out up dip structure in Midland Basin. It typically produces from a single and enormous sand interbedded with shales. The reservoir is accumulated in stratigraphic traps migrating upward from source rocks with impermeable barriers at the top. Drilling issues faced so far are losses, tight holes which led to cancellation of logging runs, poor reservoir evaluation, non-productive time and cost. Additional challenge appears during drilling when the well is deviated. Thus, a client aimed to drill these deviated wells with less drilling issues and NPT. For a successful drilling campaign, wellbore instability issues needed to be controlled and it was achieving through mud weight optimization.
A novel approach integrating acoustic measurements and petrophysical evaluation for geomechanical analysis was carried out in this field. The reservoir in-situ properties showed anisotropy due to layering which is known as transverse isotropic vertical (TIV) anisotropy. Thus, a new advance acoustic workflow has been adopted to incorporate the TIV anisotropy for wellbore stability for this analysis. In this type of anisotropic formations, Rock mechanical properties vary with different direction. Also, isotropic stress model will not be sufficient to capture the variations in properties and hence will not be a true representative of the actual case. Hence, anisotropic stress model needs to be constructed for this.
TIV anisotropy analysis was performed in the offset well using advanced acoustic processing results. Post-drill 1D-Mechanical Earth model (MEM) and wellbore stability analysis (WBS) were carried out using these results along with post-drill events. Trajectory sensitivity analysis was performed for different trajectory to generate the mud weight window. Based on the post-drill results, Pre-drill 1DMEM and WBS was carried out for planned laterals. Sensitivity on depth of damage was performed allowing certain levels of failure. Mud weight windows were calculated for each case.
This approach has reduced the wellbore instability issues and increased drilling rates. The wells were drilled with optimum mud weight at a rate of 1300ft/day effectively reducing NPT and cost.