Mass-constrained basin basement mapping

Abstract

The irregular interface model setting side by side two dense homogeneous media has found many applications in gravity-data exploration such as for petroleum and gas in sedimentary basins, groundwater resources in buried paleochannels, characterization of abandoned landfills, and variable regolith-depth mapping. Despite its simplicity and wide range of applicability, the determination of the interface position from inverting surface gravity data configures an ill-posed problem requiring specialized regularizing procedures to produce reliable results. Common approaches to obtain stable and reliable solutions require a judicious choice of regularizing functionals, each of them able to convey a desired geologic attribute that the unknown interface is expected to feature. In assuming a style that the unknown interface may have, a mathematical procedure is elected to convey such an attribute when the interface is mapped from gravity data inversion. We have developed a different approach to the interface mapping problem by imposing a common constraint that all model solutions must have, meanwhile preventing oscillations for the interface to be mapped. As a constraint that the solutions must have, we fix the volume or the cross section for 2D structures that the anomalous density structure has. This volume (or 2D cross section) is determined by applying the mass excess theorem to the measured gravity data and assuming as known the density contrast caused by the two media paired by the interface. We find that this simple formulation for the interface-mapping problem is effective in imaging a variety of basin styles without introducing specific information about the interface attributes. Our technique is applied to invert previously published gravity data in cases with good drillhole control or with a known interface.