Author(s): Krishna Persad, Krishna Persad and Associates Limited
Numerous studies since 1979 (by Persad, Talukdar, Dow, Gibson, Rodriguez and others), have established a wealth of knowledge about the source of virtually all of the oil, condensate and thermogenic gas found to date in Trinidad, namely:
- The source is the upper Cretaceous Naparima Argillites and Gautier
- In southern Trinidad the source, is oil prone and is in the oil window
- It is present throughout and thickens to the east to over 3,000 feet.
Maturation occurred during the Oligo-Miocene during the oblique collision of the South-East Caribbean with Northern South America when the source was pushed sequentially in ENE trending source kitchens. Initial migration of whole oils occurred into interbedded Upper Cretaceous submarine fans and along faults into Olig0-Miocene reservoirs Nariva, Retrench and Herrera sands.
As the Caribbean Plate advanced wrench faulting during the Pleistocene caused breaching to the entrapped oil into shallower mainly Pliocene reservoirs by a process called Evaporative Fractionation. This process leads to re-migration of lighter (mainly aromatic) liquids and thermogenic gas into shallower reservoirs in a progressive manner with gas migrating the furthest and intermediate reservoirs being charged with gas and condensate and deeper light oils. Residual oils which are heavy to very heavy and often waxy are left behind in the original reservoirs.
Fractionation can be recognised from the character of the HRGC and from the position the liquid plots on a “Thompson Diagram”. There has been a paucity of discoveries of hydrocarbons in portions of eastern and generally in far western onshore Trinidad. Many shallow wells in both areas have found little or no hydrocarbons in both areas. At the same time there has been no indication of massive oil seeps indicating breached reservoirs with loss of much of any entrapped oil and gas.
This implies that the hydrocarbons are trapped in deeper reservoirs i.e. Cretaceous and Oligo-Miocene.
Exploration drilling in both portions of the basin, more recently by Touchstone in Ortoire and by Bahamas Petroleum (formerly Columbus Energy) and previously Trinidad Exploration and Development in the South West Peninsula (SWP) and by Texaco in the near-shore SWP and geochemical work on analyses of oils in both areas and ejecta from mud volcanoes in the SWP have confirmed the potential for accumulations of oil, gas condensate and as in the Ortoire area and in the SWP This presentation the geochemistry, the discoveries to date and makes some predictions about future potential for hydrocarbons in deeper reservoirs in both areas.
Krishna Persad, Renaissance Energy Limited
Krishna earned a BSc (Special Honours) and a PhD both in Geology from the University of the West Indies.
In his 50 years of experience in the industry, he has worked in State oil companies and Private Oil Companies from 1970 to 1987. Since then have been an Independent Oil Producer. Currently, he is Technical Consultant and Co-CEO at Renaissance Energy Limited in Barrackpore Trinidad, where is responsible for providing geological and technical advice regarding new drills and production operations and advising and supporting the CEO. Krishna is Honorary Member of the Geological Society of Trinidad and Tobago. Previously active member AAPG and member SPE.