Structural evolution and its influence on the deposition of sediments, type of organic matter and hydrocarbons generated in the North Marine Area, Gulf of Paria, Trinidad, West Indies
Presented at the 6th GSTT geological conference, Trinidad, 2017
As the Caribbean Plate entered Trinidad area, interaction between the Warm Springs and the Los Bajos Faults set up a transtensional stress field that has resulted in all subsequent faults being extensional with throws down to the east. The faults were initiated in the west and new faults formed sequentially from west to east later merging to form a larger fault, the North Marine Master Fault.
The Brasso and Nariva Formations are dominated by deepwater claystones, sands to be thin and sporadically developed, with individual net thicknesses averaging 80ft and porosities ranging from 12% to 25%.
The sediments of the Manzanilla and Springvale and Talparo Formation have been interpreted to have been deposited within a WSW – ENE trending estuarine environment. Sedimentation rates kept up with the creation of accommodation space by faulting, resulting in marginal marine – inner neritic water depths. Interval thickness of the Manzanilla is +/- 5,400ft and Springvale +/- 1,700ft thick. Depths to the Top Springvale vary from -1,500ft – 6,500ft, the Top Telemaque from 4,800ft – 7,500ft, and the Mid-Miocene Unconformity from 3,000ft – 12,700ft.
The Manzanilla Formation contains multiple potential pay zones with porosities ranging from 25% to 30%. Some of these pay sands have been tested by wells but did not flow due to the low API gravity of the oil. The sands which did flow tend to have been toward the base of the Manzanilla. The Springvale, and Talparo formations tend to be gas prone, easily observed on seismic data as bright amplitudes. Individual sands can be up 100ft thick, with porosities of up to 40%.
Most of the hydrocarbons in Trinidad have been sourced from Type II kerogens contained in Cenomanian – Santonian and Aptian age marine shales of the Naparima Hill and Gautier Formations respectively, Maastrichtian and Tertiary sediments are dominated by mainly woody and coaly kerogens. Some intervals in the Telemaque are rich in amorphous kerogens. Total Organic Content for most of the interval is below 2%. Thermal Alteration Indices indicate that most of the shales are immature, a BHT vs depth plot indicates that the geothermal gradient is 1.3F/100ft.
Analysis of produced gas from wells indicate biogenic gas with minor thermogenic components. There are two (thermogenic and one biogenic petroleum systems:
the Gautier/Naparima Hill- Manzanilla/Springvale (!)
The Nariva/Brasso/ Manzanilla/Springvale (!)