The recent discovery of two thermogenic oil seeps 70 km apart onshore Jamaica, suggests that a previously unrecognised hydrocarbon system may well be present.
Windsor Gas Seep
A natural gas seep at St Ann, Windsor, in northern Jamaica is a well-known tourist attraction and money earner for locals, offering amongst other things, its healing properties (hey, whatever does it for you man!). These recent discoveries are the first reported oil seeps.
Chris Machette-Downes visited the seep and reported:
The seep is of dry gas and is guarded enthusiastically by a local Rastafarian. My attempts to sample the gas in 2006 were met with some resistance as using a gas syringes in the sacred spring was considered offensive until some Jamaican dollars were presented. The gas proved to be very dry, almost pure Methane, but with an isotopic signature that suggests that it is thermogenic in origin. The origin is unknown, but a Cretaceous or older source is indicated. The St Ann’s Great River Inlier is one of the 26 Cretaceous inliers that occur on the Island in an otherwise Tertiary setting.
Jamaica Oil and Gas Potential
The JEBCO Alliance in 2004 undertook a multiclient study and reported that of the 11 wells drilled in Jamaica, all but one encountered oil and gas shows. They identified three petroleum systems in the data with the most important being a middle Eocene pro-delat source. In the offshore Walton #1 well the middle Eocene occupied a 700 metre interval. JEBCO defined reservoir objectives within the middle Eocene, delta-associated sequence, reef sequences and detrital products. Assuming a 50% fill of the mapped carbonate targets would imply potential for 2.8 BBO or 10.6 Tcf.
The Windsor #1 well was drilled in northern Jamaica near the St Ann gas seep and encountered oils similar to others in the Caribbean Region.
Remarkably, the three broad elements that comprise the essence of the Caribbean plate (the Lower Nicaraguan Rise, or Siuna Terrane; the Upper Nicaraguan Rise, or Chortis; and part of the Great Caribbean Arc or northern periphery of the Caribbean plate or platelets) can also be identified though petroleum geochemistry. Windsor #1 well in the north of the island was drilled in a terrain that has strong affinities with the geology of the Yucatan in Mexico. If one compares the oil fingerprint, using gas chromatography-mass spectrometry and stable isotope ratio distributions, there is a near identical match with the Belmopan oil found in Belize, 1,000 km to the west. The match is so close that it is as if the Belmopan field has been cut in two, with one portion perhaps residing on the North Coast of Jamaica in what is called the North Coast Block. Chris Machette-Downes
Seep Sampling Program and Results
CGG GeoConsulting and the Petroleum Corporation of Jamaica (PCJ) have announced the discovery of two independent live oil seeps from different parts of the island of Jamaica. This significant find marks the first documented occurrence of ‘live’, or flowing, oil from onshore Jamaica and will be of particular interest to oil explorationists focused on Central America and the Caribbean.
The oil seeps were found during fieldwork for a recently completed multi-client Robertson Study (Red Book) of the petroleum potential of on- and offshore Jamaica entitled ‘Petroleum Geological Evaluation of Jamaica’ made jointly by CGG GeoConsulting and PCJ. Subsequent detailed geochemical analyses confirmed the oil seeps originate from two separate Cretaceous source rocks. These results are included within the study, which gives a detailed account of the petroleum geology of this frontier region of the Caribbean. It comprises over 1,300 new geochemical, biostratigraphic and sedimentological analyses of over 800 individual outcrop, well, corehole and seep samples collected from Jamaica.
Jamaica and its offshore basins remain relatively underexplored. Oil or gas shows have been seen in ten of the eleven exploration wells drilled to date. The discovery of these seeps indicates the presence of working petroleum systems on the island that are generating and expelling liquid hydrocarbons to the surface. The Robertson Study offers a valuable tool for oil explorationists to quickly become familiar with the geology of Jamaica and is available for purchase from CGG.
Sophie Zurquiyah, Senior Executive Vice President, Geology, Geophysics & Reservoir, CGG, said: “This exciting discovery of live oil onshore Jamaica, based on our joint study with PCJ, builds a strong case for the island as an attractive region for future oil exploration within the Caribbean. The insights and promising outcome of the study demonstrate the value that CGG’s broad geoscience expertise combined with the integration of field geology, laboratory analyses and seismic interpretation can bring for high-grading frontier regions for future oil exploration.”