Abstract: A reservoir simulator first estimates rock displacement parameters (u, v, and w) representing rock movement in the x, y, and z directions. When the rock displacement parameters (u, v, w) are determined, “?x,y,z” (the ‘x,y,z elongation strains’) and “?xy,yz,zx” (the ‘shear strains’) are determined since “?x,y,z” and “?xy,yz,zx” are function of “u”, “v”, and “w” When “?x,y,z” and “?xy,yz,zx” are determined, “?x,y,z” (the ‘elastic normal rock stress in x,y,z directions’) and “?xy,yz,xz” (the ‘elastic shear stress’) are determined since “?x,y,z” and “?xy,yz,xz” are a function of “?x,y,z” and “?xy,yz,zx”. When “?x,y,z” and “?xy,yz,xz” are determined, the rock momentum balance differential equations can be solved, since these equations are a function of “?x,y,z” and “?xy,yz,xz”. When any residuals are substantially equal to zero, the estimated rock displacement parameters (u, v, and w) represent ‘accurate rock displacement parameters’ for the reservoir.