Implementation of an elastoplastic constitutive model to study the proppant embedment in coal under different pore fluid saturation conditions: a numerical and experimental study

Proppant embedment in coal is highly concerned in both research and practice due to the vulnerability of the softer surface nature in coal and its involvement in fracture treatment failures. The issue has been reported to further intensify under pore fluid conditions; however, to date very few studies have investigated this effect for coal propped fractures. Analysing proppant embedment in numerical models through standard material models is far from realistic for materials like coal because the distinct plastic deformation stages play an essential role in proppant embedment measurements. In this study, a Drucker Prager material model is implemented, which employs the shrinking of the failure criteria by the progress of plastic deformation to consider the strain-softening behaviour of coal. The numerical results show that the implemented material model can describe the distinct deformation stages experienced in coal materials. The simulation results for uniaxial compression tests, triaxial tests and proppant embedment tests agree well with their experimental counterparts. However, comparing the simulation and experimental results show that modification of the elastic modulus alone to incorporate surface changes experienced due to pore fluid saturations, which is the primary parameter considered in proppant embedment studies may provide an underestimation for proppant embedment measurements in coal.