User:Ageary/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

The Talara Basin is a sedimentary basin that is located along the northwestern coastline of Peru that covers 11000 mi2. The eastern border of the basin is created by the La Brea-Amotape Mountains and the uplift that Talara from the Lancones and Sechura Basins. The southeastern boundary is formed by the La Casita fault and Paita High uplift. The northern limit is the Pillar of Zorritos, which is a basement uplift and fault zone. The southern boundary is the Trujillo Basin and finally the western boundary is located 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


Provincial Geology

Tectonic History

The formation of the Talara Basin province is a consequence of Paleogene era tectonic activity. The Talara Basin lies on top of a larger basin created during the Mesozoic and pre-Mesozoic era. The basin is separated from the surrounding Progreso and Sechura Basin by faulted igneous intrusions. The Talara Basin is an unusual forearc basin, inasmuch as it displays many features which are not characteristic of such a tectonic context. These features apparently result from the basin's location at the intersection of the Amazonas Aulacogen, the Andean orogenic belt, and the subduction zone of the Peru-Chile Trench.

The history of the Talara forearc basin is dominated by extensional rather than compressional tectonic activity, which reached a peak after the Eocene in association with low-angle gravity slides. This tectonism began with a prolonged synsedimentary phase, which, during the Paleocene-Eocene, generated a complex system of horsts and grabens bounded by major high-angle normal faults trending NE-SW and NW-SE [3]. The basins, instead of being forearc as there was no associated volcanic arc, were linear downwarps that filled with clastic sediments from the continent combined with shallow- and deep-water marine limestones [2].

Figure 2 North-south stratigraphic cross section across the Talara and southern Progreso Basins

Based on examination of seismic, well, aeromagnetic, and gravity data, the creation of the Talara Basin province in Paleocene and Eocene time resulted from both subduction of the Nazca Plate under the South American Plate and depositional events that were related to transtensional (pullapart) and extensional tectonics [4].

Figure 3 Geologic Map of the Talara Basin Province and surrounding basins. Purple points indicate oil and gas fields that have been developed[5][6]

Depositional History

Sedimentation occurred in 4 stages during the Paleozoic across Western South America [7].

1. Shallow-marine clastic deposition through the Devonian (Lochkovian-Frasnian), with an increase in sedimentation during the Early to Middle Devonian (Emsian-Eifelian). Lithofacies distribution and sediment thicknesses indicate primarily a western source.

2. Uppermost Devonian–lower Carboniferous (Famennian- Visean) strata are characterized by glaciomarine and fan-deltaic sedimentation. Clasts were derived from underlying sedimentary units and andesitic, granitic, and tuffaceous rocks.

3. A middle-Carboniferous (Serpukhovian-Bashkirian) hiatus in sedimentation occurred;

4. Siliciclastic and carbonate deposition occurred in late Carboniferous–early Permian time (Moscovian?-Artinskian). Intra-arc basins may have existed near presentday coastal Peru. Following the middle-Carboniferous hiatus, sedimentation continued in a back-arc region. Epeirogeny or magmatic-related tectonics may have influenced regional sea-level fluctuations and unconformities between Devonian and Carboniferous strata in Peru; during the Devonian, these events would have restricted formerly open seaways along eastern Peru, western Bolivia, and northern Argentina and Chile Tectonic activity of the Nazca Plate subducting below the South American Plate during the Tertiary caused uplift and erosion of the Andes Mountains and resulted in extensional high-angle faults that delineated horst-and-graben structures [4].

Petroleum Geology

Source Rocks

Most of the hydrocarbon source rocks in the Talara Basin province are the Albian Muerto Limestone and the marine shales of the Campanian Redondo Formation [8] . Lower Eocene Palegreda neritic marine shales and the Paleocene Balcones Shale (Mal Paso Group) are also believed to be important organic-rich source rocks in the Talara Basin Province. AIPC evaluated the total organic carbon (TOC) of 151 samples of Tertiary shales collected from outcrops and well cuttings at locations between Zorritos (just north of the Talara Basin province) and Talara (near the Portachuelo oil field). Eighty-one Eocene shales ranged from 0.11 percent to 1.92 percent TOC, 15 Mancora Shale samples ranged from 0.08 percent to 4.95 percent TOC, 35 Heath shales were 0.24 percent to 3.86 percent TOC, 13 Zorritos shales varied from 0.22 percent to 13.12 percent TOC, and 7 Cardalitos shales ranged from 0.15 percent to 1.62 percent TOC. Gonzales and Alarcon (2002) indicated that geochemical analyses of 13 shale and limestone samples that ranged in age from Early Cretaceous (Albian) to Oligocene age showed TOC contents ranging from 1.1–1.3 percent. Values above 1 percent TOC are potential source rocks, whereas those below this have low to marginal potential [9]. API gravity is an inverse measure of a petroleum liquid's density relative to that of water. Thus, comparing the API gravity in Figure 4 between the Talara Basin and Progreso Basin to the North we see that the Talara Basin oils tend to have a greater API gravity than those of the Progreso. Light oil is characterized by an API of 31°-55°, medium oil by 22°-31°, and heavy oil by anything less than 22°.

Figure 4 API gravity comparing oils of the Talara Basin and the Progreso Basin

Reservoir

The primary reservoirs are Eocene-age nearshore-marine sandstones. They are found mainly in the Upper Cretaceous Redondo Shale, and the Upper Cretaceous Ancha and Petacas Formations of the Mal Paso Group. The Paleocene-Eocene sedimentary sequence is entirely clastic and is characterized by shallow-marine, deltaic, and fluvial sandstones, marine shales, and turbidites; underlying sediments are about 75 percent clastic but include some thick and widespread oolitic, reefy, and micritic limestones that were considered to be the most important hydrocarbon source rocks[2].

Bianchi analyzed the porosity and permeability of several reservoir formations with the following results[10]

  • Hélico Formation sandstones, 12–15 percent porosity, 2–5 millidarcies (mD) permeability
  • Clavel (Pariñas), 11–19 percent porosity, 60–120 mD permeability
  • Manta (Mogollon) 8–11 percent porosity, 0.15 mD permeability
  • Basal Salinas Sand, 11–16 percent porosity, 14–20 mD permeability.

Traps and Seals

The Talara Basin is characterized by heavy block faulting due to mostly extensional tectonics during the Middle Miocene. This tectonic activity caused folding and deposition across the basin until the Tertiary age, where extensional faulting created high-angle normal faulting that produced fault-block reservoirs [2]. Structurally, the area is a system of faulted blocks—the size of the blocks is nonuniform and can vary from 100 to 1,500 acres or more [4]. Seismic records indicate a variety of trapping features for Talara and bounding basins that include rollovers and updip closures against faults, and stratigraphic pinch-outs (turbidite channel deposits) and onlap onto old highs . Interbedded and overlying marine shales are the primary reservoir seals. Some units are composed of multiple sandstones separated by shales. Lateral seals are (mainly normal) fault offsets, and lateral depositional or erosional pinch-outs of the mostly marine sandstones into shales [2].

References

  1. Higley, Debra. “The Talara Basin Province of Northwestern Peru: Cretaceous-Tertiary Total Petroleum System.” AAPG Bulletin, vol. 86, 2004, doi:10.1306/61eeeb6a-173e-11d7-8645000102c1865d.
  2. 2.0 2.1 2.2 2.3 2.4 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. Carozzi, A. and Palomano, J., Talara Forearc Basin: Depositional Models of Oil-Producing Cenozoic Clastic Systems, J. Petrol. Geol., 1993, vol. 16, no. 11.
  4. 4.0 4.1 4.2 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.
  5. 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 <http://greenwood.cr.usgs.gov/energy/WorldEnergy/OF97-470D/>.
  6. Petroconsultants, 1996, Petroleum exploration and production and PetroWorld 21 databases: Petroconsultants, Inc., P.O. Box 740619, 6600 Sands Point Drive, Houston TX 77274-0619, USA, or Petroconsultants, Inc., P.O. Box 152, 24 Chemin de la Mairie, 1258 Perly, Geneva, Switzerland.
  7. Isaacson, P.E., and Diaz Martinez, E., 1995, Evidence for a middlelate Paleozoic foreland basin and significant paleolatitudinal shift, Central Andes, in Tankard, A.J., Suarez Soruco, R., and Welsink, H.J., Petroleum basins of South America: American Association of Petroleum Geologists Memoir 62, p. 231–249.
  8. 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.
  9. 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.
  10. 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 seminar, Nov. 6–8, 1 CD-ROM, EXPR-3-CB-02.pdf, 14 p.