Abstract Parrylands is a multiple pay oil field with production from unconsolidated sand reservoirs of late Tertiary age in the Southern basin of Trinidad . Stratigraphy and sedimentology of the formations penetrated indicate three cycles of delta progradation resulting in the deposition of the Cruse, Forest, and Morne L'Enfer formations. Primary production is obtained from the deeper Cruse Formation whereas the overlying Forest and Lower Morne L'Enfer formations contain heavy oil and tar sands . The Forest 'A' Reservoir represents a delta fringe/barrier bar system containing approximately 100 million barrels of heavy oil in place. Within the Forest 'A' Reservoir, the oil occurs in north-northwest-trending barrier bars on the crest and flanks of the Lot 1 anticline. Geochemical evidence suggests that the oil was generated from a Cretaceous source and migrated along major faults into upper Tertiary reservoirs, where it occurs as a heavy degraded oil. Gravity segregation occurred resulting in 16-19°API crude in the crestal area of the anticline and 10-12°API crude on the lower flanks of the anticline. The higher API gravity crude is produced by primary methods while that of lower gravity can only be produced commercially by thermal methods . This observed phenomenon of segregation within the same reservoir is significant in identifying primary production in areas of heavy oil. This can be done by carefully mapping and correlating structure, API gravity, and other characteristics of the crude . The economic considerations of this technique in exploration and exploitation of heavy oil cannot be over-stressed since a (favorable) cash flow can be generated prior to intensive capital investment for thermal enhanced oil recovery .

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 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.