Observations from Exploration Drilling in an Active Mud Volcano in the Southern Basin of Trinidad, West Indies
Maria Henry, Michael Pentilla, Darrell Hoyer, 2011. "Observations from Exploration Drilling in an Active Mud Volcano in the Southern Basin of Trinidad, West Indies", Shale Tectonics, Lesli J. Wood
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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 Trin-idad. 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 dino-cysts 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 velocity) 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 velocity 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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The phenomenon of rocks moving under their own means has always fascinated both scientists and nonscientists alike. The 2006 AAPG Hedberg Conference on Mobile Shale Basins was held in response to a need to gather industry and academic communities in a common forum to address the very existence of mobile shales. Stimulating and informative discussions at that Conference led to this special volume on shale tectonics. AAPG Memoir 93 documents shale tectonics from a variety of basins around the world, including the southern Beaufort Sea; the Krishna-Godavari Basin, India; eastern offshore Trinidad; offshore Brunei; and along the westernmost portion of the Mediterranean Sea. The book also provides information on the petrographic framework, behavior, geometries, and geodynamic models of shales. Publication of this Memoir coincides with a growing interest in shales as hydrocarbon reservoirs, and will add to the body of literature that significantly addresses both extrusive and intrusive shales.