Comparison and Results of a Borehole Gravity Survey
with
Core and Log Data through an Allochthonous Salt Sheet in Ship Shoal South
Additions, Offshore Louisiana
DESANTIS, J. E. and H. L. HARRISON
A BHGM (Borehole Gravity Meter) survey
was conducted in the Phillips No. 1
Ship Shoal 337 well, located offshore Louisiana in the Gulf of Mexico. Gravity
readings were made at fifteen stations within the borehole through a 6,214 foot
thick salt glacier and ten readings were made at stations in the borehole below
the salt.
BHGM densities are compared to density from rotary sidewall cores and FDC density log. The BHGM data determines the average density of the salt body and core and log data are discrete samples of the salt body. Significant differences exist between the three data sets and a comparison will be presented.
The borehole is located near a steep salt flank and borehole gravity could
show a structural effect due to the proximity of the meter to a significant salt
edge. This effect alters the borehole gravity readings which yields a less than
real salt density. The magnitude of the effect could give insight to the
accuracy of the salt flank location relative to the wellbore as imaged from 3-D
seismic data. Accurate salt densities are also important in gravity modeling for
determining salt thickness and subsalt sedimentary section thickness.
Implications for selecting
the proper salt density for gravity modeling will be
discussed.