Talara basin

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Figure 1 The best known of all of Peru's coastal basins, this figure shows the extent of the Talara Basin in Northwestern Peru. (Courtesy of Zúñiga-Rivero, F., Keeling, J.A., and Hay-Roe, H, 1998)

The Talara Basin is a sedimentary basin that is located along the northwestern coastline of Peru that covers 11000 mi2. The basin is contained to the east by the uplift created by the La Brea-Amotape Mountains that divides the Talara from the Lancones and Sechura Basins. The La Casita fault and Paita High uplift creates its southeastern boundary. The northern limit is the Pillar of Zorritos, which is a basement uplift and fault zone. The basin is contained to the south by the Trujillo Basin and to the west by the Nazca Plate subduction zone[1].

The Talara Basin is arguably the best known of all of Peru’s coastal basins. For over 130 years, it has produced more than 1.68 billion barrels of oil and 340 billion cubic feet of gas, primarily from its onshore sectors [2] . Much of the basin’s reserves originate from formations that were created during the Pennsylvanian to Oligocene. The reservoirs are primarily Upper Cretaceous to Oligocene sandstones, however, the most prolific and most promising reservoirs are the Eocene sandstones[1].

Provincial Geology

Tectonic History

Paleogene era tectonic activity is the main orogeny that lead to the formation of the Talara Basin province. Stratigraphically, the younger Talara Basin lies above a larger basin created during the Mesozoic and pre-Mesozoic era. Several faulted igneous intrusions separate the Talara Basin from the even younger adjacent Progreso and Sechura Basins. There is some debate in the classification of the type of basins as it presents features unique to several types of basins.

Although the Talara Basin has been classified as a forearc basin by several scientists, others argue that the Talara and surrounding basins are indicative of “linear downwarps” [2].

Researchers argue that the reason the Talara presents atypical forearc basin features is due to its location at the junction of the Amazonas Aulacogen, the Andean orogenic belt, and the subduction zone of the Peru-Chile Trench[3]. However, others argue that due to there not being any related volcanic arcs that present due to the formation of the Talara, it is more likely a linear downwarp where marine limestones combined with clastic sediments from the continental regions filled in the newly formed basin[2].

Eocenic extensional tectonic activity was the main driving factor that drove the formation of the Talara Basin. These extensional forces resulted in “low-angle gravity slides”. In conjunction to these forces, Paleocene and Eocene sedimentary deposition resulted in a horst and graben structure that covered the region of western South America. This structure became an important feature for trapping oils and gas due to the resulting normal faulting that became associated with this structure[3].

Figure 2 North-south stratigraphic cross section across the Talara and southern Progreso Basins. (Courtesy of Debra Higley, 2004)

Depositional History

Figure 3 Geologic Map of the Talara Basin Province and surrounding basins. Purple points indicate oil and gas fields that have been developed[4].(Courtesy of Schenk, 1999 and AIPC, no date).

Sedimentation occurred in primarily 4 stages during the Paleozoic along western South America [5].

1. Early – Middle Devonian: Shallow-marine clastic deposition.

2. Late Devonian–Early Carboniferous: glaciomarine and fan-deltaic sedimentation.

3. Middle-Carboniferous: Lack of sediment deposition.

4. Late Carboniferous – Early Permian: Siliciclastic and carbonate deposition.

Figure 4 Vertical seismic display of southern Talara Basin with indicated depositional events. (Courtesy of Zuniga-Rivero, F., Keeling, J.A., and Hay-Roe, H., Attractive potential seen in 10 sub-basins off Peru, OGJ, Sept. 7, 1998, p. 117.)

Petroleum Geology

Source Rocks

The Talara Basin contains many potential hydrocarbon source rocks within its formations due to their large amount of limestones and shales. Great example of these formations include the Albian Muerto Limestone, Campanian Redondo Formation, Palegreda marine shales and the Paleocene Balcones Shale which all have shown to contain very high organic levels in their formations [5].

To determine source rock potential, the Inorganic Carbon (IC) must be subtracted from the Total Carbon (TC) of a sample to be left with the Total Organic Carbon (TOC) .In an analysis conducted by the AIPC, 151 samples of shales were studied from well cuttings and TOC percentages measured with the following results[6] :

  • Eocene Shales: 0.11 - 1.92 %
  • Mancora Shale: 0.08 - 4.95 %
  • Heath Shales: 0.24 - 3.86 %
  •  Zorritos Shales: 0.22 - 13.12%
  • Cardalitos shales: 0.15 - 1.62 %
  • Early Cretaceous to Oligocene Shales: 1.1–1.3 %

For a potential source rock to be viable for exploration, TOC levels should greater than 1%. As we can see from the results above, all formations studied produced very viable hydrocarbon source rocks with TOC values much greater than 1%[6].

API gravity is also useful to characterize the type oil oils within the formations. API gravity measures a petroleum liquid's density relative to that of water. Light oils are noted by an API of 31°-55°, medium oil by 22°-31°, and heavy oil by anything less than 22°.Thus, comparing the API gravity in Figure 5 between the Talara Basin and Progreso Basin to the North we see that the Talara Basin oils tend to have a lower API gravity than those of the Progreso indicating heavier oils than the those found in the Progreso Basin[1]

Reservoir Rocks

The Talara Basin region has gained much interest by oil companies due to the large amount of reservoir rocks found within the basin. The Talara Basin has been home to at least 40 oil fields with drilling taken place throughout many of the formations found within the area [2]. Most of the reservoirs are found near-marine and marine sandstones of the Eocene. Formations that have been observed to contained ample supply of reservoir rocks include the Upper Cretaceous Redondo Shale, Upper Cretaceous Ancha, Petacas Formations, Verdun Formation, and the Chacra and Salinas Groups[1].

The reason for this widespread localization of reservoir rocks is due to the fact that underlain beneath these layers, much of the sedimentary deposition that occurred during the Paleocene and Eocene included shallow marine deltaic shales and limestones. Furthermore, these layers also consisted of oolitic and micritic limestones which all promote the accumulation of hydrocarbons in the source rocks within the formations underlying the reservoir formations[2].

A potential reservoir rock must satisfy the criteria of porosity and permeability to be considered viable for drilling. Porosity, the measure of the pore space between sediment grains, should be around 10 – 40 % to be considered viable. In addition to this, permeability should measure around 10 to 100s mllidarcys (mD). However, with new improved technology and methods of extracting oil and gas, permeability can be augmented by methods of horizontal drilling and fracking to increase drilling opportunities. 

In the Talara Basin several formations were analyzed to measure porosity and permeability respectively[7]:

  • Clavel: 11–19%, 60–120 mD
  • Figure 6 Cross-Section of the Talara and Sechura Basins showing the widespread system of horsts and grabens that resulted from extensional faulting[8].
    Manta: 8–11%, 0.15 mD
  • Basal Salinas Sand: 11–16%, 14–20 mD.
  • Hélico Formation Sandstones: 12–15 %, 2–5 mD

Although permeability is not the most ideal, the porosity of the sampled reservoir rocks allows this region to be a suitable source for extraction using alternative methods of drilling.

Traps and Seals

There  are several stratigraphic and structural reasons that the Talara Basin has produced suitable traps to contain the reservoir rocks. The entire region was subject to heavy extensional tectonic activity during the Miocene which lead to large-scale block faulting. Additionally, this tectonic activity also produced wide-spread folding of the layers which all contributed to the formation of traps and seals[2]. In general, the entire Talara Basin province is representative of nonuniform faulted regions that can range from 100 to 1,500 acres[9]. Stratigraphically, the Talara Basin consists of rollvers, updip closures, and pinchouts which act as trapping mechanisms. The folding produced by the extensional tectonic activity caused the shales overlying the reservoirs to act as anticlinal seals [2].

Further Reading

References

  1. 1.0 1.1 1.2 1.3 Higley, Debra. “ The Talara Basin Province of Northwestern Peru: Cretaceous-Tertiary Total Petroleum System.” AAPG Bulletin, vol. 86, 2002, doi:10.1306/61eeeb6a-173e-11d7-8645000102c1865d
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Zúñiga-Rivero, F., Keeling, J.A., and Hay-Roe, H., 1998b, Peru onshore-deepwater basins should have large potential: Oil and Gas Journal, Oct. 19, 1998, p. 88–95. V. Carozzi, A & R. Palomino, J. (2007). The Talara forearc basin, NW Peru: depositional models of oil-producing Cenozoic clastic systems. Journal of Petroleum Geology. 16. 5 - 32. 10.1111/j.1747-5457.1993.tb00728.x.
  3. 3.0 3.1 V. Carozzi, A & R. Palomino, J. (2007). The Talara forearc basin, NW Peru: depositional models of oil-producing Cenozoic clastic systems. Journal of Petroleum Geology. 16. 5 - 32. 10.1111/j.1747-5457.1993.tb00728.x.
  4. Schenk, C.J., Viger, R.J., and Anderson, C.P., 1999, Maps showing geology, oil and gas fields, and geologic provinces of South America: U.S. Geological Survey Open File Report 97-470D, 1 CD-ROM, [Adobe Acrobat v. 4.0 pdf format], URL
  5. 5.0 5.1 Gonzales, E., and Alarcon, P., 2002, Potencial hidrocarburifero de la cuenca Talara: Lima, Peru, Ingepet 2002 seminar, Nov. 6–8, 1 CDROM, EXPR-1-EG-07.pdf, 15 p.
  6. 6.0 6.1 American International Petroleum Corporation (AIPC), no date, A review of the petroleum potential of the Tumbes Basin, Peru: Denver, Colorado, American International Petroleum Corporation, 46 p.
  7. Bianchi, R.C., 2002, Sistema petrolero, mechanismos de entrampamiento de fluidos en el campo Litoral. Cuenca Talara— nor oeste del Peru: Lima, Peru, Ingepet 2002
  8. Hermoza, Wilber & E, Martinez & J, Fernandez & Calderon, Ysabel & C, Galdos & Bolanos, Rolando. (2006). Structural style of the offshore Talara and Tumbes forearc basin.
  9. Raez Lurquin, M.A., 1999, Tectonica en la cuenca Talara costaafuera, nor-oeste Peru Exploration and exploitation of petroleum and gas: Lima, Peru, Ingepet ’99 seminar, Oct. 26–29, 1 CD-ROM, EXPR-1-MR-12.pdf, 19 p.