The incorporation of geophysical, petrophysical and geological constraints in gravity modeling to resolve structures at depth.

Abstract

Gravity modeling is an important tool for interpreting and understanding geological structures in the subsurface. In forward modeling or inverse modeling, the main goal is to modify a geophysical/geological model to accomplish an acceptable level of reproducibility in the observed data. However, due to the non-uniqueness of potentialfield data, more than one model might fit the observed data. In order to reduce the number of acceptable models, constraints are commonly incorporated into the model. There are countless studies available in the literature demonstrating the necessity of constraining gravity and magnetic models. However, typically they do not demonstrate the individual enhancements that come as a consequence of integrating each constraint into the geophysical model. This study demonstrates how the model, either inverse or forward, is improved as new constraints are built into the modeling workflow. The constraints include information from a density compilation, high-resolution seismic sections, geological maps as well as geological interpretations. The mapped surface geology and the density of this surface data were important to explain the gravity variations associated with faults and to estimate the dip and the error in this dip estimation. The high-resolution seismic sections were helpful to identify reflective features that were most likely lithological contacts where there could be changes in density. Incorporating some of these deeper features and the gradual changes in depth evident in the seismic data resulted in changes in the thickness of the near-surface rocks that was more consistent along strike. Information from previous studies in the area, such as geological interpretations of seismic sections, were required to ensure the geological feasibility of gravity models.