Hydrocarbons were first noted in the Guyana-Suriname region by Dutch explorers in the 1750’s. Onshore discoveries of biodegraded heavy oil in Suriname supported the presence of a working petroleum system. In 2000, the United States Geological Survey (USGS) identified the Guyana-
Suriname Basin as having an estimated mean recoverable oil reserves of over 13.6 billion barrels of oil, and gas reserves of 32 trillion cubic feet.
After numerous unsuccessful wells, some with shows, the Liza-1 discovery was announced in May 2015 by ExxonMobil, and was the first significant
oil find offshore Guyana. The well encountered more than 295 feet (90 metres) of high-quality oil-bearing sandstone Upper Cretaceous turbidite sandstone reservoirs. The gross recoverable resources from the Stabroek Block are now estimated to be nearly 11 billion oil equivalent barrels, with over 30 discoveries to date.
The Stabroek Upper Creteacous discovery trend has now been extended by Apache and Total into Block 58 in Suriname, and into the Guyana Corentyne Block by CGX and Frontera. Drilling on the Demerara Rise to date has yet to yield a commercial discovery. Here, we examine the key controls on broader play and prospect trends within the region.
Structural template
The Mesozoic tectonostratigraphic development of the Guyana-Suriname region, associated with the opening of the Equatorial and Central Atlantic Oceans, exhibits periods of extension, transpression and compression. The development of the Demerara/Guinea Transform Margin Plateau and adjacent regions through the Jurassic and into the Early Cretaceous provided a structural template, which in turn influenced the develop of post-rift depositional systems. These are thought to have a first order control upon the hydrocarbon prospectivity of the margin, particularly the deposition and thickness distribution of ~4% Total Organic Carbon (TOC) Albian to Coniacian source rocks and the prolific Upper Cretaceous turbidite sandstones in the basin.
Additional Source Rock
Besides the prolific Cretaceous source rocks, numerous hydrocarbon seeps are evident above the Demerara Rise. This could be an indication of an additional Jurassic-aged source, particularly in the Nickerie and Commewijne Grabens on the present day shelf, along with 2.5% TOC sediments proven in the Takutu graben onshore. These grabens are interpreted to be part of a failed rift systems related to the earliest phase of Atlantic opening, and serve to influence the position of long-lived deposition systems, fed recycled Precambrian sediments from the Guyana Shield, into terrestrial and marine systems from the Cretaceous onwards.
Canyon-fed reservoirs
Passive burial through the Late Cretaceous continued with deposition of substantial thicknesses of turbidite sandstones and pelagic shales.
These sediments fed directly through the shelf and slope via a series of deep-water canyons from the quartz rich Guyana Shield. Seismic facies indicate the presence of channel-lobe complexes, with high porosity and permeability reservoirs occurring across the play.
Quantitative interpretation of reservoir units often proves challenging to differentiate between wet and pay sands. It may be just as important to understand the 3D nature of the sealing lithologies, along with sandstone pinchout and internal heterogeneity relationships in fully determining the stratigraphic trapping potential of these units.
Monocline
Subtle topography may have been present at the time of deposition, with a monocline persisting through the Cretaceous and Cenozoic lying directly above older lineaments. The location of this monocline, which was identified by Trude et al. (2022), approximately lines up with the Basement Hingeline as shown on the map on the previous page. On that basis, prospectivity south of the hinge line is thought to be more limited than to the north.
Regional scale inversion and drainage reorganisation during the Cenozoic led to the emplacement of mass transport complexes fed from shelf-slope, which led to the generation of petroleum at the present day.
More than Cretaceous turbidites
Aside from the prolific Upper Cretaceous turbidite sandstone discoveries, the Ranger-1 discovery in the NE portion of the Stabroek licence proved the presence of hydrocarbons in Lower Cretaceous carbonates, deposited on a relic volcano, which is dated as Aptian by Casson et al. (2021). Other volcanic features are noted upon the Demerara Rise.
The Joe-1 and Jethro-1 wells drilled by Tullow on the Guyana slope proved the presence of pay in the Paleogene section, but are thought to be sub-commercial.
Extending the current extent of proven plays across the margin is dependent upon understanding the distribution of Cretaceous source
and reservoir rocks. These are determined by inherited structural features, leading to either preferentially thick deposition, or controlling sediment distribution across the depositional system. In turn, rapid burial is required to lead to generation of hydrocarbons. The Jurassic potential may depend more upon further 3D seismic investigations, which may form part of the work programs in recent auctions.
References
Blaizot, C., 2021. Suriname: Demerara Plateau Oil and Gas Potential. GeoExpro, September 2021.
Casson, M., Jeremiah, J., Calvès, G., de Ville de Goyet, F., Reuber, K., Bidgood, M., Reháková, D., Bulot, L., and Redfern, R. 2021. Evaluating the segmented post-rift stratigraphic architecture of the Guyanas continental margin. Petroleum Geoscience, 27 (3).
Chisholm, T., 2020. Hess’s journey into an emerging super basin and ultra-high impact exp-loration for an independent E&P company. Houston Geological Society Sheriff Lecture, November 9th, 2020.
Museur, T., Graindorge, D., Klingelhoefer, F., Roest, W., Basile C., Loncke L., and Sapin F., 2021. Deep structure of the Demerara Plateau: From a volcanic margin to a Transform Marginal Plateau. Tectonophysics, March 2021, Volume 803.
Olyphant, J. R., Johnson, R. A., & Hughes, A. N. (2017). Evolution of the Southern Guinea Plateau: Implications on Guinea-Demerara Plateau formation using insights from seismic, subsidence, and gravity data. Tectonophysics, 717, 358-371.
Staatsolie and Envoi 2023. Offshore Suriname Demerara Bid Round (DBR) 2022. Synopsis March 2023.
Trude, J., Kilsdonk, B., Grow, T., and Ott, B., 2022. The structure and tectonics of the Guyana Basin. From: Nemčok, M., Doran, H., Doré, A. G., Ledvényiová, L. and Rybár, S. (eds.). Tectonic Development, Thermal History and Hydrocarbon Habitat Models of Transform Margins: their Differences from Rifted Margins. Geological Society, London, Special Publications, 524.
