Compression of Particulate Materials in Wellbore Fractures and Enhancement in the Wellbore Breakdown Limit

Abstract

Fluid loss during subterranean drilling often occurs through fractures that develop or preexist around the wellbore. Particulate additives, known as lost circulation material (LCM), are commonly added to the drilling fluid to mitigate lost circulation. The LCM forms an impermeable agglomerate within the fractures while preventing further tensile failure of the wellbore wall. The outcome is enhancement in the wellbore breakdown limit. A semi-analytical elastic solution is developed to estimate the width of near-wellbore fractures that partially close on the LCM agglomerate. The solution uses stress–strain data from confined compression testing on LCMs. The compression test results are modeled through a modified form of Kawakita’s (1971) powder compaction equation. The developed constitutive model is embedded within the described semi-analytical solution for the wellbore fractures. The solution adopts an incremental loading approach to treat the nonlinearities arising from the characterized LCM constitutive behavior, as well as large deformation of the LCM agglomerate within the partially closed fractures. At each incremental load, the nonlocal stress equilibrium along the fracture length is described via an integral equation. Successive solutions to these integral equations determine the unknown fracture width of partially closed fractures. A competition between the fractures tendency for propagation and the wellbore wall tendency for secondary tensile failure determines the overall stability of the fractured wellbore. Mechanical behavior of the LCM agglomerate under compression is identified as a key parameter that controls both mechanisms, thereby, the gain in breakdown limit of a fractured and LCM-treated wellbore.