Lost circulation material design for near-wellbore transverse fractures

Abstract

The use of particulate lost circulation material (LCM) in drilling fluid is a common method for mitigating lost circulation from near-wellbore fractures that develop during subterranean drilling. Fracture width estimation is the center piece of designing the particle size distribution (PSD) of LCM blends. Width estimation of near-wellbore fractures has predominantly been based on assuming axial fracture development from wellbores. However, this assumption is not valid for all wellbore orientations. Shallow vertical and highly inclined or horizontal well sections in a normal subsurface faulting regime may give rise to configurations where drill-induced fractures develop transverse to the wellbore axis. A transverse fracture yields a substantially different width compared to an axial fracture. This study aims to demonstrate the width contrast between the two fracture geometries and the impact that such contrast would have on the LCM blend design. For this purpose, the width of near-wellbore transverse fractures is estimated using a linear elastic fracture mechanics solution to an axisymmetric model of the same. Contrary to the case of hydraulic fractures, the solution must consider the effect of wellbore cavity boundary conditions on the fracture width profile. Two case studies involving horizontal and vertical boreholes are examined. Results indicate that the assumption of axial fracture geometry could lead to substantial underestimation or overestimation of the fracture width depending on the wellbore inclination and magnitudes of the in-situ stress components. Application of the solution in selecting the compositions of blends made from three LCMs is demonstrated. The discrepancy between the LCM blends PSDs obtained based on the axial and transverse models of the wellbore fracture are discussed.