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Abstract

Henry, Maria, Michael Pentilla, and Darrell Hoyer, 2010, Observations from exploration drilling in an active mud volcano in the southern basin of Trinidad, West Indies, in L. Wood, ed., Shale Tectonics: AAPG Memoir 93, p. 6378.

DOI:10.1306/13231308M933418

Copyright copy2010 by The American Association of Petroleum Geologists.

Observations from Exploration Drilling in an Active Mud Volcano in the Southern Basin of Trinidad, West Indies

Maria Henry,1 Michael Pentilla,2 Darrell Hoyer3

1Henry GeoConsulting Services, Inc., Littleton, Colorado, U.S.A
2Target Surveys, Westminster, Colorado, U.S.A
3Hoyer Petrophysics, Inc., Fort Collins, Colorado, U.S.A

ACKNOWLEDGMENTS

The authors appreciate the support of Trinidad Exploration and Development Company Unlimited for the permission to publish this article. In addition, contributions from the following companies and individuals are acknowledged: Petrotrin, Richard Sams, Latinum/Ichron, BioStrat, Clyde Ramkhalawan, Krishna Persad, International Logging SA, Bernd Gehre, and GX Technology and Generation Services. This article benefited immensely from comments by Lesli Wood, Keith Jagiello, and Bruce Eggertson.

ABSTRACT

The Trinidad Exploration and Development Company drilled the Habanero 1 well within Trinidad's southern basin in an area of surface mud volcano flows and vents. The well location is along a trend of mud volcanoes that extends across northern Venezuela and southern Trinidad. The upper 3200 ft (975 m) of the well drilled through interbedded mud volcano layers as confirmed by palynology, paleontology, lithology, well log, and seismic information. Below 3200 ft (975 m), the well drilled primarily country rock deposits of the upper Miocene through Pliocene Cruse Formation. Paleontology and palynology data give an age range of Eocene through Miocene for the mud volcano material; the highest recovery of foraminifera and dinocysts were from the Oligocene–Miocene Cipero and Lengua formations.

Several drilling problems were encountered, especially in the shallow, mudflow-rich part of the hole. Drilling issues included lost circulation intervals and the necessity for high mud weights (up to 17.5 ppg), to control high pressures. The well encountered numerous oil and gas shows, but no commercial hydrocarbons were tested.

Seismic data in the area illustrate a downward-tapering cone of disruption around mud volcano vents, with numerous faults providing conduits for the flow of mud. Drilling samples confirmed this interpretation, because the zones described as faulted commonly coincided with an influx of exotic mudflow material.

Subsurface logs measured decreased resistivity, lower density, and higher interval transit time (slower Previous HitvelocityNext Hit) in mud volcano layers relative to intervals of country rock formations. These intervals are anomalous even when compared to log data for overpressured shale zones in neighboring wells. The Habanero 1 checkshot survey documents shallow mud volcano layers with velocities slower than the Previous HitvelocityTop of water, perhaps caused by the presence of entrained gases within the matrix of the mud. Refraction static velocities are also anomalously slow around Habanero 1 and along the trend of mud volcanoes.

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