Applications of a Continuum Damage Mechanics Model to Hydraulic Fracturing

Abstract

ABSTRACT A fracture propagation model that is intended to describe the geometry of a hydraulic fracture is also supposed to replicate the pressure level and trends during execution. This is often not the case with "abnormally high fracturing pressures" recorded presently. The problem stems from the intrinsic nature of linear elastic fracture mechanics. A relatively new branch of fracture mechanics, Continuum Damage Mechanics (CDM), has been used by the authors to construct a fracture propagation model describing fracturing pressure behavior consistently. The CDM version of the Perkins-Kern/Nordgren model (CDM-PKN) contains a combined parameter responsible for fracture propagation retardation. The parameter is the CDM substitute for the fracture toughness. The new parameter can be identified from step-rate tests and/or treatment pressure diagnostics. Knowing this parameter the CDM-PKN model can be used to predict the net fracturing pressure, fracture length, width and fluid efficiency. In this work several applications of the model are presented. A laboratory experiment, step-rate tests and a minifrac test are evaluated in terms of the new model. A possible range is established for the combined parameter. The large impact of the combined parameter on fracture design is illustrated by a case study.