Mapping Gas-charged Fault Blocks Around the Vinton Salt Dome, Louisiana Using Gravity Gradiometry Data

Reflection seismic imaging of complex faulting and associated petroleum reservoirs adjacent to onshore salt domes in the Gulf Coast region is both expensive and time consuming. Modeling studies show that gravity gradiometry data have the resolution in ideal conditions to image such reservoirs where seismic is unavailable or cost averse. Full Tensor Gravity Gradiometry (FTG) data, which are higher resolution than conventional gravity data, have been acquired by Bell Geospace over the Vinton salt dome located in southwest Louisiana. A model of the dome incorporating reflection seismic, well logs, VSP, and conventional gravity interpretations was built and input to a FTG forward calculation program. The resulting signal was subtracted from the recorded survey to remove the overpowering signal of the dome. This residual image revealed anomalies linked to subsurface structures such as faults, gas-charged reservoirs, and parts of the salt dome not included in previous studies. Models of gas-charged reservoirs were produced and input to the forward calculation program to compare the results with anomalies found near the dome. Negative Eötvös anomalies on the Tzz component of the residual image are observed within the maximum boundary of the salt dome. The distribution and amplitudes of these anomalies are used to discriminate between signals caused by salt and signals caused by reservoirs. Oil and gas production data overlaid on the FTG data show production within areas with signal character for gas-charged reservoirs.