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, wherein the simplified 3D rock representation of the subsurface rock structure is an approximation of the subsurface rock structure generated using one or more of a discrete Fourier filtered representation, a wavelet filtered representation, or a transition probability matrix with spatial correlations; 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 structural representation has the petrophysical properties of the subsurface rock structure and can be used to simulate additional petrophysical, geology and reservoir properties.