Wellbore Strengthening Geomechanics: An Engineering Design Workflow to Help Minimize Risk of Induced Lost Circulation

Abstract

Abstract Induced lost circulation in depleted sandstone formations is a risk in most deepwater drilling operations, often leading to costly operational delays involving remedial treatments. Wellbore strengthening (WBS) using lost circulation material (LCM) to plug an estimated fracture width is one approach to minimizing this risk of lost circulation. However, most simulations for estimating fracture widths are either numerical or linear elastic models that do not account for wellbore inclination, azimuth, and different stresses. WBS planning involves fracture width estimation, which are kept propped open by LCMs. However, LCM blend selection is not often included in the wellbore strengthening workflow. In this work, a detailed field-friendly engineering workflow is presented that can estimate induced fracture widths accommodating wellbore inclination, azimuth, and different stresses around wellbore. The model also includes an LCM property referred to as "LCM blend stiffness," estimated using stress-strain data on different LCMs using a hydraulic press. The workflow accommodates varying LCM blends and, in turn, stiffness, to estimate maximum equivalent circulating density (ECD) providing wellbore wall and fracture-tip stability. The estimated fracture width from geomechanics-based WBS engineering model was first compared with the existing linear elastic model under the same conditions and results were within 10% variation. Using inputs from a major operator in Gulf of Mexico under the same conditions, the estimated induced fracture width was approximately 70% wider with the geomechanics based model that included wellbore inclination, azimuth and stress anisotropy compared to the current simple linear elastic model. LCM blends with different stiffness values were used as inputs into the model, and maximum ECD gain was estimated that provided both wellbore wall and fracture-tip stability. The analyses will also highlight the limitation with the model for due consideration in the solution selection. A geomechanics-based wellbore strengthening workflow is presented, which uses an analytical solution to uniquely solve for stresses around the wellbore with fractures, and a methodology for balancing wellbore wall and fracture-tip stability. The workflow aids in the selection of an optimal LCM combination that can provide maximum permissible ECD gain thereby stabilizing the wellbore wall (minimizing secondary fractures) and the fracture-tip (preventing fracture propagation). This is the first time that a geomechanics-based wellbore strengthening workflow accommodates LCM property and provides an estimation of fracture-tip stability.