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Houston Geological Society Bulletin


Houston Geological Society Bulletin, Volume 43, No. 7, March 2001. Pages 23-23.

Abstract: Garden Banks 625 - A Deepwater Gulf of Mexico Post-Previous HitDrillNext Hit Review


Mark Sunwall1 and Robert Alexander1
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-Previous HitdrillNext Hit 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-Previous HitdrillNext Hit 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-Previous HitdrillTop 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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