--> ABSTRACT: Three-dimensional Inverse Modeling Of Geothermal Heat Flow Anomalies Associated With Salt Diapirs, by Seiichi Nagihara; #90906(2001)

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Seiichi Nagihara1

(1) Texas Tech University, Lubbock, TX

ABSTRACT: Three-dimensional Inverse Modeling Of Geothermal Heat Flow Anomalies Associated With Salt Diapirs

The perturbation of geothermal field by salt diapirs has been the interest of many researchers. A salt diapir, being more thermally conductive than other sedimentary rocks, funnels geothermal heat flow and causes a positive anomaly within the sediments above. The shape and amplitude of this anomaly reflect the geometrical shape of the salt body. The geometry of a buried salt body may therefore be constrained by theoretically inverting the surface heat flow observations. The spatial information is useful in the subsalt petroleum exploration in the Gulf of Mexico, where seismic techniques have difficulty imaging the bases of allochthonous salt structures. Here I present a fast inversion method for constraining the salt bottom geometry in three dimensions. The method utilizes the simulated annealing optimization algorithm to determine a thermal conductivity structure model that yields the smallest misfit between the model-predicted and the observed heat flow variations. The model consists of a number of rectangular blocks, each of which can have a different thermal conductivity value. The inversion algorithm tests many different combinations of conductivity values by performing importance sampling of the model parameter space. For each parameter combination, it obtains the forward heat flow response, using the finite difference method. Fast computation of the forward solution is achieved by solving the finite difference matrix equation with the biconjugate gradient method. To reduce the problem of non-uniqueness, the inversion method utilizes additional constraints such as the salt top geometry, which can be obtained from conventional seismic coverage, and continuity of the salt body.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado