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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Garden Banks 625 - A Deepwater Gulf of Mexico Post-Drill Review
By
1Exploration Manager
2Advanced Geoscientist, Texaco
The Garden Banks 625 prospect was drilled in September 1998 to test several bright spots associated Pleistocene objectives in a salt-withdrawal mini-basin. This post-drill review briefly compares and contrasts the results of this dry hole to a recently drilled 100+ MMBOE discovery nearby. This presentation was originally part of the HGS "Gulf of Mexico Dry Hole Seminar" held November 8, 2000.
Pre-drill technical analyses for this well included 3D seismic
interpretation, AVO, instantaneous frequency, seafloor piston
core geochemistry, and 3D acoustic impedance inversion
calibrated to several wells within the basin. The integrated data
suggested a strong likelihood of reservoir-quality sands with a
good chance for hydrocarbon saturation. AVO analysis indicated
a strong class III response at both objective levels within the
trap. A high GOR oil was predicted as the most likely hydrocarbon
phase based on data collected from oil-saturated seafloor piston
cores. Top seal
capacity and lateral stratigraphic pinch-out
integrity were assessed to be the highest geologic risk attributes
owing to the shallow depth of burial below mud-line (5000-8000'),
the apparent lack of reflector terminations and interval thinning
at the limit of amplitude anomaly in the deepest objective level.
The well results confirmed the presence of high-quality
Pleistocene sand reservoirs as predicted. Post-drill log analysis,
well-tie synthetic seismogram and mud log data showed that the
sands had low gas saturations of 10-20%. Wellcuttings and wireline
sonic confirmed the lack of adequate compaction to
generate a top seal
capable of trapping a commercial column of
hydrocarbons. Seals that did form were subject to rupture due
to frequent movement of allochthonous salt within the
mini-basin. Several named tropical storms and hurricanes
complicated drilling and logging operations and resulted in an
incomplete wireline log suite to evaluate the deepest objective.
The well was plugged and abandoned on November 4, 1998.
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