Columbus basin

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Fig. 1 General breakdown of the oil and gas concentrations in the Columbus Basin[1]

The Columbus Basin is a foreland basin located off of the southeast coast of Trinidad and Tobago, within the East Venezuela Basin. Due to unique formation factors, the basin has a special structural and stratigraphic profile. The Columbus basin has allowed high petroleum and hydrocarbon production for a number of years, with a large amount of proven reserves present, as can be seen in Figure 1. The structure is quite large, covering about 14,000 km^2[2]. Two major structural trends are present in the Columbus basin, and account for much of its potential as a hydrocarbon storage system. The features include a series of east-northeast anticlines and north-northwest oriented normal faults.[3]

Tectonic History

The Columbus Basin formed through a series of tectonic events that led, eventually, into the Basin seen today. Eastward migration of the Caribbean plate relative to the South American plate formed a 1100 km long basin along Trinidad and Tobago and Venezuela.[4] Middle Miocene thrusting related to convergence thrusting of the Caribbean plate and the passive margin of Northern South America allow continued thrusting and transpression into an oblique-like foreland basin. Subsequently, early Pliocene normal faults along the top of the cretaceous passive margin were triggered by over-steepening related to formation of the downdip, which is more seaward than the Columbus Basin. Large transfer faults connect normal faults that are driven mainly by gravity. These trend in the downslope direction. Lastly, present day plate movements are due to Pliocene-Recent strike-slip faults parallel to the trend of the Darien ridge. [4]

Depositional History

Sedimentation of the Basin occurred in three main stages, and can be visualized in Figure 2:

  1. Cretaceous-Cenozoic: Cenozoic age clastic rocks overlaying Cretaceous age carbonate rocks
  2. Lower Miocene-Upper Pliocene: Thick siliciclastic rocks overlay a laterally thick mobile shale system. High sediment accumulation rates and low permeability trap water in these shale layers and result in an abnormally high hydrostatic pressure
  3. Early Pleistocene-Recent: Shale diapirism continues, as evidenced by active mud volcanoes observed on the seafloor.[5]
Fig. 2 Geographic breakdown of time period in depositional environment[5]

Petroleum Geology

Source Rocks

Having a somewhat complex geological background, and being an offshore basin, most data about the source rocks in the Columbus Basin comes from inferences drawn when referencing geological data about kerogen types, Oil and Gas production, type of oil, type of gas, etc. What is documented is that a majority of the source rock for the basin comes from Upper Cretaceous source rocks that extend from a belt of rock that goes across the entire northern margin of the South American craton.[5]

More specifically, the rocks belong to the organic-rich siliciclastic marine rock that is consistent with a source rock change throughout the region from mainly carbonate to siliciclastic. The type of petroleum produced from these marine rocks varies greatly over the geography of the basin. The northwest region of the basin is primarily oil dominated (60%-70%), and the southeast region of the basin is primarily gas dominated (~90%).[5] The metrics for the source rocks are approximated as follows:

  • TOC (Total Organic Content)>6 wt%
  • HI (Hydrocarbon Index)=450-700mg HC/g TOC

Generally, to warrant exploration, TOC levels should be above 1%. As shown above, the levels are the basin are much greater than 1%, making the structure potentially attractive for exploration and production companies.

Reservoir Rocks

The Basin being offshore allows for a unique geological makeup in its history, formation, and now in its reserves. The composition of the reservoir rock is mainly deltaic sandstone of the Miocene and Pliocene. There is, however, potential for Lower Tertiary and Upper Cretaceous sections of the basin.[2] The reason for this spread of reservoir rock is due to the geologic timeline of the formation. The siliciclastic rock laid over carbonate rock is evidence of the shift in depositional environment that took place in that region of South America. During that time, hydrocarbon formation was still occurring, and the reservoir rocks were shifting, allowing multiple types of reservoir rocks to be seen and some still to be proven.

Traps and Seals

The traps of the Columbus Basin are mainly structural, with normal fault traps formed by transtension associated with wrench faulting along the wide fault zone of the southern margin of the Caribbean plate. Traps formed in the transpressional segments of the fault zone are also present.[1] Seals are mainly intraformational mudstones of the Pliocene deltaic section.[2] As mentioned before, the mudstone/shale traps the water, and subsequently the hydrocarbons formed beneath them, to create a seal on the formation. These seals can be seen dotted across the basin where the mudstone/shale appears, but are not found everywhere in the basin.

Fig 3 This figure shows the history and current numbers about production in the Columbus Basin[6]
Fig 4 This image shows the history of production in the Columbus Basin[7]

Migration

Migration was mainly along the numerous growth faults associated with the progradation of the Orinoco delta, and migration was also along vertical along faults associated with the wrench fault zones. The timing of growth faulting was Miocene and Pliocene, and wrench faulting was late Pliocene and Pleistocene in the Columbus Basin.[2]

Future Petroleum Potential

The Columbus Basin has produced petroleum for an extensive period of time, allowing many of the major oil companies to make a profit in the area. Looking at future potential in the area, many of the production will be focused on natural gas. As seen in Figure 3, there are 33 tcf of reserves in the basin.[6] The current gas production is around 3 bcf/day and oil production is around 40,000 bbl/day.[6]The reason that many of the future production of the Basin falls into natural gas can be seen by Figure 4, in that since 2006, the production of gas continues to surpass that of oil.[7]

Petroleum and Engineering Facilities

Due to the basin being located off the shores of Trinidad and Tobago, many of the engineering aspects of production take place on either semi-submersible rigs or jack-up rigs. On many of these rigs, the equipment is quite heavy. A platform can weigh 4,600 tonnes and be 120 m tall.[8]This poses an unusually difficult task for accessing many of the petroleum reserves within the basin. A flowline must be placed from the well to a hub somewhere nearby, making the 10 km journey for petroleum that much more difficult.[8] Many production wells are linked to each other, whether through flowlines or other means of completing the well-to-hub system. Maintenance on the offshore rigs also proves a challenge, as whenever a well needs to be fixed, it can't be producing. Getting out to the rigs in less than ideal weather provides another engineering problem to overcome.

Further Reading

Tectonostratigraphic Framework of the Columbus Basin, Eastern Offshore Trinidad

Chronostratigraphy and tectonostratigraphy of the Columbus Basin, eastern offshore Trinidad

BPTT updates gas reserves in Columbus basin in Trinidad and Tobago

References

  1. 1.0 1.1 Marcelle-De Silva, J., Thomas, A., De Landro Clarke, W. L., & Allum, M. (2012). Evidence of gas hydrates in block 26—offshore Trinidad. Energies, 5(5), 1309–1320. https://doi.org/10.3390/en5051309
  2. 2.0 2.1 2.2 2.3 Schenk, C. J. (n.d.). Trinidad Basins Assessment Unit 60980201 - USGS. Retrieved December 11, 2021, from https://certmapper.cr.usgs.gov/data/PubArchives/WEcont/regions/reg6/p6/tps/AU/au609821.pdf.
  3. Leonard, R. (1983). Geology and hydrocarbon accumulations, Columbus Basin, offshore trinidad: Abstract. AAPG Bulletin, 67. https://doi.org/10.1306/03b5b231-16d1-11d7-8645000102c1865d
  4. 4.0 4.1 Garciacaro, E., Mann, P., & Escalona, A. (2011). Regional structure and tectonic history of the obliquely colliding Columbus Foreland Basin, offshore Trinidad and Venezuela. Marine and Petroleum Geology, 28(1), 126–148. https://doi.org/10.1016/j.marpetgeo.2009.08.016
  5. 5.0 5.1 5.2 5.3 Gibson, R. G., Dzou, L. I. P., & Greeley, D. F. (2004). Shelf petroleum system of the Columbus Basin, Offshore Trinidad, West Indies. I. Source Rock, thermal history, and controls on product distribution. Marine and Petroleum Geology, 21(1), 97–108. https://doi.org/10.1016/j.marpetgeo.2003.11.003
  6. 6.0 6.1 6.2 Trinidad's Oil and Gas industry. Maribo Resources Ltd.. (2018). Retrieved December 11, 2021, from http://www.mariboresources.com/FocusRegion_Trinidad.aspx?tab=3.
  7. 7.0 7.1 Mclean, S., Charles, D., & Rajkumar, A. (2021, February). Navigating transfer pricing risk in the oil and gas sector: Essential elements of a policy framework for Trinidad and Tobago and Guyana. researchgate.net. Retrieved December 7, 2021, from https://www.researchgate.net/publication/349849243_Navigating_transfer_pricing_risk_in_the_oil_and_gas_sector_Essential_elements_of_a_policy_framework_for_Trinidad_and_Tobago_and_Guyana.
  8. 8.0 8.1 Matapal Gas Project, Columbus Basin, Trinidad and Tobago. NS Energy. (2021). Retrieved December 11, 2021, from https://www.nsenergybusiness.com/projects/matapal-gas-project/.