North Caspian Basin
Contents
Introduction
The North Caspian Basin is a petroleum rich basin located in Kazakhstan and Russia. The Caspian sea region is one of the oldest producing oil fields in the world and is currently an important resource for energy generation in the region. The offshore and onshore deposits of the region present challenges to producers, but high yields continue leading the exploration of the basin. Along with some of Azerbaijan's oil production, the Caspian region became a significant source of oil production for Russia and the Soviet Union.
Geological
This basin originated from being bounded by the Paleozoic carbonate platform of the Volga-Ural province in the north and west and by the Ural, South Emba, and Karpinky Hercynian fold belts to the east and south. Although the basin was created by pre-late Devonian rifting and spreading across the ocean crust, the exact time period of these events is unknown. The sedimentary zones of this basin exceed more than 20 km thick in the most centralized area of the basin. Six units have been identified in the North Caspian Basin, four of which include Paleozoic subsalt rocks of the basin margins. <ref>[1]
History of the Basin
The North Caspian Basin was formed from several linear rift systems that intersect within Russia and Kazakhstan. These intersecting rifts created a circular area within the deep ocean crust, which can be problematic since most rifts create angular bends. This variation of rift is extremely unusual and has created rumors of the production of the zone. Around the Ordovician time sediments began to fill the basin, continuing into the Devonian and Carboniferous. The basin became much like the Permian Basin during the Devoinain era. By the Kungarian, collisions which assembled the Kazakstan Continent helped lift regions around the deep Caspian Basin which led to the creation of the Kungarian salt in the basin which is 4-5 kilometers thick. The salt was then buried by sediments and created large salt domes deep within the subsurface. <ref>[2]
Petroleum Geology
Trap & Seal
Permian salt laying over deep Devonian reef complexes formed a seal, which prevented hydrocarbons from migrating to the surface and escaping the reef areas. Carbonate reefs are very important trap aspects of these subsurface subsalt rocks. Atoll and pinnacle reef traps contain the largest hydrocarbon accumulations. Multiple of the fields are created in structural anticlinal traps, which are related to the Hercynian compressions formed during the Permian-Triassic time period when hydrocarbons were at peak generation. Arches in depressions and semi-arches against the slopes of the salt domes have recently been found by more modern seismic equipment. <ref>[3]
Source Rock and Migration
Indicated by the sedimentation and facies architecture of the area, the petroleum source rocks in the North Caspian Basin tend to be basinal black-shale facies along with Paleozoic carbonate platform deposits on basin margins. Due to the lack of exploration and the 20 kilometer deep source rocks, exploration has slowed and led to a lack of information on the geochemical characteristics of the basin. Source rocks in this basin have been characterized as ranging from 1.3 to 10 percent hydrocarbon potential. The idea of a presence of hydrocarbons has been heavily disputed and some scientists believe that oil pools in the salt dome traps could be high generators of hydrocarbons. The most important stage of hydrocarbon production in the shallower areas of the basin was in the Late Permian-Triassic time. <ref>[4]
Reservoir
This reservoir is interesting because it has multiple different areas of the field which act as completely different reservoirs depending on where the well is drilled. In the Karachaganack field, porous limestones and dolomites aid to a 10-14 percent porosity. In other regions such as the Upper Devonian/Middle Carboniferous carbonate reservoir rocks lend a porosity of 2-20 percent and averages 6 percent. In this same region small oil discoveries have been made in the sandstones, but most wells have tested low due to extensive depths and overpressures. Most of these wells did not exceed tens of barrels a day with an exception of one well which produced nearly 2,000 barrels per day. These sandstones are poorly sorted but have a locally high content of carbonate cement which is detrimental to the porosity and permeability. Along with this area is the Izembet Formation, which has tested high permeability and porosity. Some oil accumulations have been discovered in the Kenkiyak field, which has depths from 4-4.5 km and a porosity from 5-11 percent. The main problem with this reservoir is the sandstone beds, which is a result from progradational deposition of the organic compounds. Properties of Jurassic and Cretaceous sandstones that occur at shallow depths near the salt domes have proved to have 25-35 percent porosity and high permeability. <ref>[5]
Future Potential and Challenges
Kashagan, a large shallow-water field, is one of the most prominent fields located in the North Caspian Basin. This field was one of the first offshore developments in Kazakhstan, which began production in October 2016. This field currently has multiple different operators, including North Caspian Operating Company, Shell, Total, Eni, ExxonMobil, CNPC, and Inpex. This field, developed as Kashagan phase one, is the largest current international investment in Kazakhstan at $55 billion. Phase one, known as the Experimental Program (EP) reached its maximum design output capacity in 2019 of 380,000 barrels per day (bopd). The Kashagan field has plans to continue phases into the Full Field Development Programme which would raise the fields output to around 1.5 million barrels of oil per day (mbopd). As of August 2019, the Kashagan field produced a cumulative total of 30 million tonnes of crude oil, more than 8.44 billion cubic meters (bcm) of gas, and 1.75 million tonnes (Mt) of sulphur. The Caspian Basin projects are relatively far from export markets, which requires large investments in infrastructure to move oil to ports for global exports. Difficulty in transporting infrastructure and resources in the Caspian basin is another challenge due to freezing of the seas and having to use canals to move important infrastructure such as drilling equipment. Shifting legal and regulatory frameworks between the many countries within the basin also leads to large challenges for foreign investment in the region. <ref>[6]
<ref>[7]
References
“U.S. Energy Information Administration - EIA - Independent Statistics and Analysis.” International - U.S. Energy Information Administration (EIA), https://www.eia.gov/international/analysis/regions-of-interest/Caspian_Sea.
Ulmishek, Gregory F. “Petroleum Geology and Resources of the North ... - USGS.” USGS, 2001, https://pubs.usgs.gov/bul/2201/B/b2201-b.pdf.
Gibson, Richard. “August 27. North Caspian Basin.” History of the Earth, 1 Jan. 1970, http://historyoftheearthcalendar.blogspot.com/2014/08/august-27-north-caspian-basin.html.
“Kashagan Oil Field Development, North Caspian Sea, Kazakhstan.” NS Energy, https://www.nsenergybusiness.com/projects/kashagan-oil-field-development/.
“Paleozoic.” Paleozoic | U.S. Geological Survey, https://www.usgs.gov/youth-and-education-in-science/paleozoic#:~:text=Paleozoic%20(541%2D252%20million%20years,the%20geologic%20timescale%20was%20made.&text=Paleozoic%20signposts%20are%20colored%20green.
“Devonian.” Wikipedia, Wikimedia Foundation, 12 Dec. 2021, https://en.wikipedia.org/wiki/Devonian#:~:text=The%20Devonian%20(%2Fd%C9%AA%CB%88,of%20the%20Carboniferous%2C%20358.9%20Mya.
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