Anisotropic tomography with rock physics constraints

Anisotropic tomography with rock physics constraints

Yunyue Li, Dave Nichols, Konstantin Osypov, and Ran Bachrach

Abstract:

Anisotropic model building is a challenging problem, well-known for its non-linear and underdetermined nature. To reduce the null-space and stabilize the inversion, we propose a new preconditioning scheme in linearized tomography to include rock physics prior information. We introduce the rock physics information in the form of covariance among P-wave vertical velocity ($v_0$ ), $\epsilon$ and $\delta$ , and is generated by stochastic realizations of a compacting shale model. We design a VSP synthetic survey with the common industry geometry on two different examples, of which one fulfills the assumption of our rock physics model and the other does not. The results show that by utilizing the proper rock physics prior information, tomography can better resolve the anisotropy parameters, especially in the area where inversion is poorly constrained by the data. However, precautions should be taken when the lithology of the subsurface is largely unknown. Finally, we perform a posterior uncertainty analysis to evaluate the contribution of the rock physics prior information. The results show that the null-space is greatly reduced by introducing the prior information.

Anisotropic tomography with rock physics constraints