Interpretation of tensor gravity data using an adaptive tilt angle method

Abstract

Full Tensor Gravity Gradiometry (FTG) data are routinely used in exploration programmes to evaluate and explore geological complexities hosting hydrocarbon and mineral resources. FTG data are typically used to map a host structure and locate target responses of interest using a myriad of imaging techniques. Identified anomalies of interest are then examined using 2D and 3D forward and inverse modelling methods for depth estimation. However, such methods tend to be time consuming and reliant on an independent constraint for clarification. This paper presents a semi‐automatic method to interpret FTG data using an adaptive tilt angle approach. The present method uses only the three vertical tensor components of the FTG data (Tzx, Tzy and Tzz) with a scale value that is related to the nature of the source (point anomaly or linear anomaly). With this adaptation, it is possible to estimate the location and depth of simple buried gravity sources such as point masses, line masses and vertical and horizontal thin sheets, provided that these sources exist in isolation and that the FTG data have been sufficiently filtered to minimize the influence of noise. Computation times are fast, producing plausible results of single solution depth estimates that relate directly to anomalies. For thick sheets, the method can resolve the thickness of these layers assuming the depth to the top is known from drilling or other independent geophysical data. We demonstrate the practical utility of the method using examples of FTG data acquired over the Vinton Salt Dome, Louisiana, USA and basalt flows in the Faeroe‐Shetland Basin, UK. A major benefit of the method is the ability to quickly construct depth maps. Such results are used to produce best estimate initial depth to source maps that can act as initial models for any detailed quantitative modelling exercises using 2D/3D forward/inverse modelling techniques.

Depth from extreme points method for gravity gradient tensor data

“…It is shown that the scaling function plots of ridge1 and ridge2 of g xz andg yz are different ( Fig. The average depth of cap rock is about 200-300 m. The results are in agreement with previous research and the geologic information available (Oliveira and Barbosa 2013;Salem et al 2013;Geng et al 2014;Zhou 2015). Therefore, for the field FTG data, we need to calculate the average value of the seven scaling exponents.…”

“…Due to the needs of increased data volume and improved accuracy, several gravity and gravity gradient tensor data processing methods have recently been proposed. The adaptive tilt-depth method was used to interpret gradient tensor data, and satisfactory results were obtained with regard to accuracy (Salem et al 2013). Therefore, demand for the interpretation methods of gradient tensor data has increased in geologic research.…”

Determining the depth of certain gravity sources without a priori specification of their structural index

“…Different values of N should be chosen for different models before depth estimation (Salem et al, 2007(Salem et al, , 2013Cooper, 2011Cooper, , 2012Fairhead et al, 2011). However, in real potential field interpretation, the buried source type is unknown.…”

“…Cooper (2012) generalized the method and applied it to gravity data depth estimation by identifying circular contours of the ratio of the vertical to the total horizontal derivative with sphere and vertical cylinder models. Salem et al (2013) added a scale value characterizing the source type into the equation of tilt angle to estimate the location and depth of simple buried gravity sources. However, these methods all need the prior information of the source type before calculating the buried depth.…”

Depth Estimation Method Based on the Ratio of Gravity and Full Tensor Gradient Invariant

“…Then, it was developed into the gradient tensor form to interpret gravity and FTG data by (ZHANG et al 2000). The same as Euler deconvolution method, Tilt-depth method also was modified to interpret FTG data (SALEM et al 2013). Analytic signal method for FTG data was established (BEIKI 2010).…”