1. A computer-implemented method for use in modeling a geomechanical reservoir system, comprising: receiving, through a computer system, data indicative of physical properties associated with the geomechanical reservoir system; generating, through a computer system, fracturing predictions by solving a system of partial differential equations that model the geomechanical reservoir system; wherein the system of partial differential equations comprises a reservoir flow model, a geomechanical model, and a fracture model of the geomechanical reservoir system; wherein the system of partial differential are coupled through a fully-expanded Jacobian; wherein the solving of the system of partial differential equations comprises solving simultaneously in a single timestep the fully-expanded Jacobian based upon the received physical properties data; and wherein the fracturing predictions model the geomechanical reservoir system for the timestep; and outputting or displaying, through a computer system, the generated fracturing predictions.