Cericia Martinez

3D Inversion of Airborne Gravity Gradiomentry For Iron Ore Exploration In Brazil

We present the 3D inversion results of gravity gradiometry data over iron ore deposits in Minas Gerais, Brazil. The host formation for the iron ore is largely the Caue Itabirite, along with the overlying Gandalera Formation and, to a lesser degree, the underlying Batatal. Consequently, the iron ore bodies have a distinctly high density contrast and produce well defined anomalies in airborne gravity gradiometry data. We have carried out a preliminary study to apply a 3D inversion to a 20-km2 subarea of data from a larger survey to demonstrate the utility of such an algorithm both in delineatng the ore deposit and in estimating the reserves. We focus on three components of the data (Tzz, Txz, and Tyz). The commonly discussed Tzz component is sufficient to produce geologically reasonable and interpretable results, while including the two horizontal components increases the resolution of the recovered density model and improves the ore delineation.

Lithologic characterization using airborne gravity gradient and aeromagnetic data for mineral exploration: A case study in the Quadrilátero Ferrífero, Brazil

AbstractWe present a study on utilizing airborne gravity gradient and magnetic data to characterize an iron ore formation in Minas Gerais, Brazil. The target iron ore bodies have a distinctly high density contrast and produce well-defined anomalies in airborne gravity gradiometry data. The high-grade hematite iron ores are associated with low and moderate susceptibility, making magnetic data useful in distinguishing potential ore bodies from the host iron formation. The airborne gravity gradient and magnetic data over part of the Gandarela Syncline iron formation in the Quadrilatero Ferrifero are independently inverted to obtain a 3D susceptibility and density contrast model. These detailed 3D physical property distributions of subsurface features are then used for geologic characterization and interpretation purposes through lithologic associations. We outline two approaches to link the two physical property distributions and identify representative geologic units in the study area. The geologic units ar...

Inversion of regional gravity gradient data over the Vredefort Impact Structure, South Africa

We present the results for 3D inversion of gravity gradiometry data over the Vredefort Impact Structure in South Africa. With the rapidly growing field of gravity gradiometry, an investigation into the extraction of information from multiple components is warranted. Though the gradient tensor has five independent components, any combination of the components can be used to invert for a structural representation of the subsurface. In an effort to understand how differing component combinations contribute to the resolution of the model, we use two measured and one calculated gravity gradient component from the Falcon system for inversion. This inquiry focuses on regional geologic features in the context of inversion with select gravity gradient components over the Vredefort impact structure in South Africa.

Lithologic characterization using magnetic and gravity gradient data over an iron ore formation

Magnetic and gravity gradient data over part of the Gandarela Syncline iron formation in the Quadril´ atero Ferr´ ifero have been utilized to obtain a 3D susceptibility and density contrast model using inversion. It is possible to use these detailed 3D physi- cal property distributions of subsurface features for lithologic interpretation purposes. We group the two physical property distributions into geologically representative units. A distribu- tion of these lithologic units can then be organized in a model similar to the susceptibility and density distributions in order to help characterize subsurface structure.

Constraining gravity gradient inversion with a source depth volume

Efficiently extracting the maximum amount of information from gravity gradient data is challenging. Interpretation often takes place in either the data domain or model domain. Here, we present a workflow that utilizes two interpretation techniques that can result in better characterization of the subsurface. Using a method that estimates depth to source, we obtain a depth volume of estimated source locations. The depth volume is then used to constrain inversion of gravity gradient data in the form of a reference model and 3D model weighting. We demonstrate that this combined approach improves the ability to recover sources at depth.

Oil and gas development footprint in the Piceance Basin, western Colorado

Understanding long-term implications of energy development on ecosystem function requires establishing regional datasets to quantify past development and determine relationships to predict future development. The Piceance Basin in western Colorado has a history of energy production and development is expected to continue into the foreseeable future due to abundant natural gas resources. To facilitate analyses of regional energy development we digitized all well pads in the Colorado portion of the basin, determined the previous land cover of areas converted to well pads over three time periods (2002-2006, 2007-2011, and 2012-2016), and explored the relationship between number of wells per pad and pad area to model future development. We also calculated the area of pads constructed prior to 2002. Over 21million m2 has been converted to well pads with approximately 13million m2 converted since 2002. The largest land conversion since 2002 occurred in shrub/scrub (7.9million m2), evergreen (2.1million m2), and deciduous (1.3million m2) forest environments based on National Land Cover Database classifications. Operational practices have transitioned from single well pads to multi-well pads, increasing the average number of wells per pad from 2.5 prior to 2002, to 9.1 between 2012 and 2016. During the same time period the pad area per well has increased from 2030 m2 to 3504 m2. Kernel density estimation was used to model the relationship between the number of wells per pad and pad area, with these curves exhibiting a lognormal distribution. Therefore, either kernel density estimation or lognormal probability distributions may potentially be used to model land use requirements for future development. Digitized well pad locations in the Piceance Basin contribute to a growing body of spatial data on energy infrastructure and, coupled with study results, will facilitate future regional and national studies assessing the spatial and temporal effects of energy development on ecosystem function.

energySim: an R package Spatial

Petroleum resource assessments provide statistical insight into the scale and spatial occurrence of oil and gas accumulations. Similarly, environmental or ecological assessments provide insight into the extent and patterns of ecological resources associated with ecosystems in a region. energySim is an implementation of an approach to link subsurface petroleum resources with ecological resources found at the land surface. The approach relies on Monte-Carlo simulation to estimate the potential impacts of oil and gas development by using assessments of continuous petroleum resources, along with quantitative relationships between petroleum development and changes in environmental or social measures.

Archaeological Investigation of the Court Kiva In Chaco Canyon Using Geophysical Methods

In this talk, we present results from geophysical investigations, including DC resistivity, FEM, and magnetic method conducted within Chaco Culture National Historical Park. In particular, we focus on data gathered within the plaza of one of the great houses, Chetro Ketl, in search of a buried kiva. The Court Kiva, as it is referred to, is known to be buried within the plaza region of Chetro Ketl from early archaeological excavations. However, following its infill and the passage of time, its location, boundary, depth and depth extent have been lost. Using geophysical methods, we have confirmed the existence and identified the location of this missing kiva. We have also gained valuable insight into the predicted geophysical responses of these desired archaeological targets for broader and ongoing investigations within the Park.