From Deep Horizon to Deep Water, a North Eastern Latin America Success Story, for some
Hydrocarbons have been commercially produced in Trinidad and Tobago for more than 100 years, the majority of which is extracted from shallow Plio-Pleistocene deltaics both onshore and offshore on the Present Day shelf. The discovery of the giant El Furrial Cretaceous shelfal sandstones in Venezuela in the 1980's caught the attention of Exxon, who followed the structural and stratigraphic trend into the more politically stable part of the Eastern Venezuelan Basin, in Trinidad and Tobago. Regional 2D seismic data was acquired, processed and deep tests were done by the drill bit in the 1990's. Consistently, the wells encountered well developed deep water turbidites but with sub-commercial volumes. The conclusion was that the multiple phases of structural deformation in the Trinidad area had severely altered Cretaceous traps, allowing secondary and tertiary migration, and the establishment of many compartments within large anticlinal features. The most southerly of these wells, however, encountered multiple limestone units and gave hints of longstanding unconformities. Drilling in the Suriname and Guyana area, the offshore Guiana Basin, began in the 1960's with many wells encountering thick shelfal Cretaceous sandstones with some having traces of bypassed hydrocarbon. Many wells, guided by 2D seismic encountered thick Eocene to Cretaceous limestones strongly suggesting a thriving carbonate system on the north eastern Latin American shelf albeit prone to multiple unconformities. Counter clockwise rotation of Africa and South America during the Cretaceous rifting and drifting phase resulted in subtle thick-skinned folding and uplift of the southern rim of this basin, giving rise to the onshore heavily biodegraded Tambarejo oilfield in Suriname, with folded Paleocene fluvial to deltaic sandstones sitting on well cemented Cretaceous turbidites. The conclusion drawn by many a company in the Guiana Basin was the lack of a competent updip seal, possible remigration due to subtle structural events and no shortage of thief zones in Darcy quality overlying reservoirs, meant that finding a large prospect was unlikely. Political tensions also brewed between Guyana and Suriname for many years until the maritime boundary was firmly established in 2007. Similarly, the over 100-year-old dispute between Venezuela and Guyana on their shared maritime boundary reached a tipping point in 2015 after Exxon’s Liza-1 discovery well in Guyana’s deepwater. This matter has since been referred to the International Court of Justice by the United Nations. Interest and activity in the Guiana Basin re-emerged in 2011 with Tullow's bold Atlantic Mirror Theory and the test of which yielded the Zaedyus discovery in French Guiana. The following dry Zaedyus wells by Shell stirred doubts along the margin that even though one may find a single large discovery it may not be sufficient to develop in this environment, political landscape, level of country development and the ever-changing price of oil. The big players having realized the ever increasing risks, have gone boldly into the deep and ultra deep, armed with some of the largest and sophisticated 3D seismic surveys in the world. The aim, is to find a large undisturbed deepwater turbidite, image its updip trap and tie it back to its provenance on the rifted Guiana Shield and its carbonate rich shelf, ensuring it isn't being cannabalized by younger turbidites and that its porosity isn't being occluded by the ever possible influx of carbonate material. A few players have tried and failed despite full 3D seismic coverage. ExxonMobil on the other hand has just registered their 8th discovery in Guyana's part of the Guiana Basin pushing reserves to 3.7BBO, first production carded for March 2020.
AAPG Datapages/Search and Discovery Article #90340 ©2018 AAPG Geoscience Technology Workshop, Deep and Ultra Deep Petroleum Systems, Beijing, China, October 26-28, 2018