1. A computer implemented joint-inversion method for creating a 3D rock representation of a subsurface rock structure using petrophysical data, the method comprising: a) storing a plurality of acquired data sets related to a subsurface rock structure, wherein the datasets comprise measured petrophysical properties of the subsurface rock structure, in at least one computer storage media; b) executing, on a computer system comprising one or more processors configured to communicate with the computer storage media and execute one or more computer programs configured to generate a simplified 3D rock representation of the subsurface rock structure with a reduced number of variables, wherein the variables represent an approximation to the subsurface rock structure; c) generating, by the computer system, a 3D rock representation from the simplified 3D rock representation; d) forward modeling, by the computer system, a plurality of petrophysical properties on the 3D rock representation to generate predicted petrophysical properties; e) comparing, by the computer system, the predicted petrophysical properties and the measured petrophysical properties; f) modifying, by the computer system, the variables of the simplified 3D rock representation using a global optimization method and repeating operations c) to f) until convergence of the predicted petrophysical properties and the measured petrophysical properties is reached; and g) generating, by the computer system, an optimized 3D structural representation from the simplified 3D rock representation found at convergence; wherein the optimized 3D rock representation has the petrophysical properties of the subsurface rock structure and can be used to simulate additional petrophysical, geology and reservoir properties.