This paper presents an integrated, multi-disciplinary approach to exploration in a complex salt basin. The construction of the interval velocity/depth model and the resultant depth migrated seismic data were constrained by gravity/magnetics and, uniquely, by structural restoration of both seismic data and interpretations to ensure consistency between geophysics and geology. This proved invaluable as it placed boundaries on interpretation possibilities in areas where poor seismic imaging persisted. A 1D basin modeling exercise was also performed adding to the complete understanding of the basin. As this work flow allowed for “what-if” scenarios, estimates of uncertainty in image quality, trap, sand distribution, etc. were also provided and used in prospect risking. The project was completed in the same time frame that it would take to complete a conventional pre stack depth migration project yet delivered far more than just depth migrated seismic data.
Although the gravitational effect of Earth’s atmosphere has relatively small values it is generally recommended to account for it in precision gravimetry. Since the effect is height-dependent, it is especially worth considering when the survey covers a broad range of gravity station heights and where the survey is performed close to a continental coast. Previously, the Earth''s topography was not considered significant when calculating the atmospheric correction for subtraction from the theoretical ellipsoidal gravity at the station. In fact the Earth''s surface is not flat over the continents and this variation in height must produce an additional influence upon the values of such a correction. We show using several examples that accounting for the Earth’s topography significantly changes the values from those calculated in the conventional way. The necessary calculations can be efficiently performed using a newly derived formula for the gravitational effect of a spherical shell with variable density.
Introduction Full tensor gravity gradiometry is becoming more commonplace within exploration projects where the benefits of high resolution, multi-component data is proving invaluable for discerning both deep and shallow structures. This paper will demonstrate how the signals measured by gradiometers achieve this by presenting a series of simple examples. Exploiting multi-tensor measurements When a full survey is conducted over an area with adequate sampling then, within the limitations of signal to noise and a few constants of integration, it is possible to predict the gravitational potential and any of its associated derivatives using measurements of only a single field quantity. Common methods of achieving this include Fourier transformations (integration and differentiation in the spatial frequency domain) and equivalent source inversions. For these ideal surveys, measuring multiple components of gravity or gravity gradient serves only to increase the accuracy rather than the ...
A group at Scripps Institution of Oceanography, in partnership with industrial sponsors (primarily StatoilHydro), has developed instrumentation over the past decade that provides new capabilities for deep ocean gravity measurements. The instrument is based on the commercially available Scintrex CG5 quartz spring sensor. We have packaged that sensor in a compact gimbal frame and housed it in a deep ocean pressure case. We have deployed the sensor in two different modes. In the first, we make repeated campaign observations at stationary positions on the seafloor with a Remotely Operated Vehicle (ROV) to monitor changes with time in reservoir density associated with production. In the second, we mount the instrument in an Autonomous Underwater Vehicle (AUV) to facilitate exploratory surveys in the deep ocean, closer to the source than could be experienced with ocean surface observations. The stationary time-lapse surveys have been underway for several years now and we have achieved a precision of about 3 microGal (3 × 10