Characterization of elastic mechanical properties of tuscaloosa Marine shale from well logs using the vti model

To avoid steep declines in the Tuscaloosa Marine Shale production, wells are fracture-stimulated to release the hydrocarbons trapped in the matrix of the formation. An accurate estimation of Young’s modulus and Poisson’s ratio is essential for hydraulic fracture propagation. In addition, ignoring the highly heterogeneous and anisotropic character of the Tuscaloosa Marine Shale can lead to erroneous stress values, which subsequently affect hydraulic fracture width estimates and the overall hydraulic fracturing process. An empirical 1D geomechanical model which takes into account VTI anisotropy is developed and used to characterize the elastic mechanical properties of the Tuscaloosa Marine Shale in two wells. In the analyzed formation, vertical Poisson’s ratio is less than the horizontal Poisson’s ratio, which suggests the necessity of an alternative to the ANNIE equations. The stiffness coefficients C13 and C11 were estimated using the relationships developed from the ultrasonic core data available for the two Tuscaloosa Marine Shale wells. Further, correlations between the static and dynamic properties from laboratory tests were used to improve minimum horizontal stress calculation. The paper compares VTI Young’s moduli, Poisson’s ratios and minimum horizontal stress with the isotropic solution. VTI modeling improves the estimation of the elastic mechanical properties. The isotropic solution underestimates the minimum horizontal stress in the formation. Moreover, it was shown that the 20-foot shale interval below the Tuscaloosa Marine Shale base is characterized by a low Young’s modulus and may be a frac barrier.