Historical development of the gravity method in exploration

Abstract

The gravity method was the first geophysical technique to be used in oil and gas exploration. Despite being eclipsed by seismology, it has continued to be an important and sometimes crucial constraint in a number of exploration areas. In oil exploration the gravity method is particularly applicable in salt provinces, overthrust and foothills belts, underexplored basins, and targets of interest that underlie high-velocity zones. The gravity method is used frequently in mining applications to map subsurface geology and to directly calculate ore reserves for some massive sulfide orebodies. There is also a modest increase in the use of gravity techniques in specialized investigations for shallow targets. Gravimeters have undergone continuous improvement during the past 25 years, particularly in their ability to function in a dynamic environment. This and the advent of global positioning systems (GPS) have led to a marked improvement in the quality of marine gravity and have transformed airborne gravity from a regional technique to a prospect-level exploration tool that is particularly applicable in remote areas or transition zones that are otherwise inaccessible. Recently, moving-platform gravity gradiometers have become available and promise to play an important role in future exploration. Data reduction, filtering, and visualization, together with low-cost, powerful personal computers and color graphics, have transformed the interpretation of gravity data. The state of the art is illustrated with three case histories: 3D modeling of gravity data to map aquifers in the Albuquerque Basin, the use of marine gravity gradiometry combined with 3D seismic data to map salt keels in the Gulf of Mexico, and the use of airborne gravity gradiometry in exploration for kimberlites in Canada.

Geophysical perspective on the structural interference zone along the Neoproterozoic Brasília and Ribeira fold belts in West Gondwana

“…Gravity data processing is a well-established procedure with plenty resourceful descriptions of mathematical aspects, method revisions and good practices (Blakely 1996, Milligan & Gunn 1997, Nabighian et al 2005a, La Fehr & Nabighian 2012. Processing and interpretation of magnetics and gravity data follows the potential field theory and and are described by relatively similar mathematical operations (Blakely 1996).…”

“…Gravity modeling applications are widespread as data are relatively easy to access via public surveys, with well-established and powerful processing techniques becoming faster and reliable (Nabighian et al 2005a), also in integrative interpretation in Global Information Systems and 3D-modeling suites. The use of geophysics presents a possibility to unveil crust geometry with patterns sometimes not envisioned just on field observation, such as effects caused by overburden or cryptic structures (Nabighian et al 2005a,b, Thomas et al 2008, Stewart & Betts 2010.…”

Unravelling the internal architecture of the Alnö alkaline and carbonatite complex (central Sweden) using 3D models of gravity and magnetic data

“…This is still a topic of research and there are many ways to separate the regional fields (e.g., Li and Oldenburg, 1998b;Nabighian et al, 2005). After testing a few simple methods, we decided to use a first-order polynomial surface (Figure 6a) fitted to the observed gravity data to represent the regional gravity field.…”

A Short Walk along the Gravimeters Path

“…Pendulum measurements are affected by several sources of errors, the main ones being: the vibration of the pendulum support, the change in the pendulum length and the influences of nongravitational forces (friction, magnetic and electrostatics). A comprehensive overview of the development of instruments, measuring techniques and application is given in Nabighian et al [5].…”