RUB' alkhali

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Brief introduction of Rub’ alkhali

The Rub’ alkhali (Empty Quarter) is a sand dessert that covers a large area south of the Arabian Peninsula (650,000 km2). This includes countries like Oman, Saudi Arabia, the United Arab Emirates, and Yemen. It is thought to be the most-oil rich area in the world, and that was confirmed when the largest oil field “Ghawar” was found there in the year 1948. However, the area still remains to be underexplored with only two oil producing fields Shaybah and Ramlah, and one gas field Kidan[1]


Rub’ alkhali geologic history

The Rub alkhali basin dates back to the Precambrian, and its first regional tectonic movement was caused by the late Ediacaran unconformity[2]. This was later followed by the pre-Siq unconformity which affected both the southwestern and western edges of the basin. The area experienced an extensional tectonic phase throughout the early Paleozoic. This extensional tectonic phase resulted in a regional Carboniferous unconformity. Transitioning into the Early Permian the basin went through a back-arc extension which triggered the emergence of the Khuff Formation[3] that included rock types such as halite and anhydrite. And during the Early Triassic the tectonic movement slowly changes into a passive margin setting as shown in (Figure 1).

Going into the early Mesozoic the passive tectonic movement continued and deposited most of the sedimentary sequence that would make up the main reservoirs. It is also important to note that the basin experienced two different stages of tectonic uplift where one is recorded at the end of the Cenomanian and another that is recorded in the mid-Santonian. The uplifting lasted from 25 to 18 Ma.[4] With the compression that was a result of the Alpine orogeny still active during the Paleogene and Neogene the Zagros thrust belts and folds began to form. Moving to the Quaternary period we see that the active margin section of the basin included sediments such as silt, clay, sand and conglomerates that are deposited in sand dunes.

figure 1: tectonic features of the area by Pollastro, R.M.

Petroleum system

The petroleum systems found in this basin are defined as the Total Petroleum system. These systems have been defined by the USGS and a few are listed below: 1. Qusaiba formation (Silurian) 2. Hanifa formation (Jurassic) 3. Tuwaiq formation (Arabian Sub-basin) 4. Natih formation (mid- cretaceous)

Seal

The minor reservoirs including the Carboniferous Unayzah and the Devonian Jubah are sealed by the shales and evaporites that overlay them. However, the evaporites (tight carbonates and anhydrites) of the Khuff formation are thought to be the main seal for this region.

Source rock

The Qusaiba formation that dates around the Ordovician- Silurian make up the main total petroleum system and the shale found in that formation are the source rocks[5]. The shales found in this formation are organic-rich hot shales. These source rocks are the tools that charge the Khuff Formation as well as the minor reservoirs found in the area (Figure 2).

Figure 2: the source rock by : Wender et al., 1998

Trap

The traps formed in this basin by the compression that took place in the eastern region. This compressional phase took place during the Late cretaceous and continued throughout the early Paleogene- Neogene. And the two major tectonic events associated with these traps are the rifting that took place along Zagros and the Alpine orogeny (Figure 3).

Figure 3: traps in the basin by Pollastro, R.M.

Primary and secondary reservoir

The primary reservoirs are the sandstones found in the Mid-Qusaiba, Unayzah and Juaf. As well as the Khuff formations. The Khuff formation consisted of sandstones, shales, limestones, dolomites, and evaporites. The secondary reservoirs mainly of Triassic dated formations. These formations consisted of shale, mudstone, sandstone, dolomites and gypsiferous.

HC type/ maturation

The hydrocarbons form in multiple traps due to the source rocks of the Silurian. The expulsion of these hydrocarbons equates to about one trillion barrels of oil that could have been trapped from the source rocks with the consideration of losses caused by secondary migration. [6]

Geologic uncertainty

The uncertainty surrounding the Rub’ Alkhali basin was mainly due to the challenges that came with the interpretation of the 3D Seismic Data Analysis in the Shaybah oil field. This was caused by the complex topography in that area. Another uncertainty is the insufficiency of data due to the complexity of the terrains[7].

Petroleum potential of the area

During the petroleum exploration of this area the most successful method used was the long-range refraction that used the Hith anhydrite as the its refractor. A study conducted in 2019 by USGS inferred that the basin could potentially contain about 242 undiscovered oil fields. Which would produce 4- 8192 million oil barrels and average of 267 gas fields which has an estimated volume of 24- 98,304 billion cubic feet.[8]

Petroleum potential of the area

During the petroleum exploration of this area the most successful method used was the long-range refraction that used the Hith anhydrite as the its refractor. A study conducted in 2019 by USGS inferred that the basin could potentially contain about 242 undiscovered oil fields. Which would produce 4- 8192 million oil barrels and average of 267 gas fields which has an estimated volume of 24- 98,304 billion cubic feet. [8]

Petroleum and Facility Engineering aspects

When looking at the area that the Rub’ Alkhali basin covers and compare it to the amount of oil and gas fields are established we find that the area is extremely underdeveloped and under explored. Saudi Aramco has made an effort to focus its efforts into exploring this area again given the new technologies we have at the moment. The company has worked on two projects the oil field expansion project and the natural gas liquids recovery project. Both are meant to increase the production in the two extablished gas and oil fields Shaybah oil field and Kidan gas field. The project has already increased the production of crude oil from ~750,000 barrels/day to 1 million barrels/day. So far, the company reported 145 oil wells have been drilled and ~645 km of the pipeline infrastructure has been laid.[9]


Reference

1. Saudi Aramco to speed up Empty QUARTER gas field development. (2013, January 24). Retrieved April 08, 2021, from https://2b1stconsulting.com/saudi-aramco-to-speed-up-empty-quarter-gas-field-development/

2. Alireza Bashari, R., Sverre Planke ( VBPR), J., & Trevor Burchette, C. (2016, February 19). Khuff: A major reservoir. Retrieved April 08, 2021, from https://www.geoexpro.com/articles/2016/02/khuff-a-major-reservoir

3. Ali, M., Aidarbayev, S., Searle, M., & Watts, A. (2018, January 17). Subsidence history and Seismic stratigraphy of the WESTERN musandam peninsula, OMAN–UNITED Arab EMIRATES Mountains. Retrieved April 08, 2021, from https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017TC004777

4. Hayton, S., & Jaeger, H. (2017, November 13). Organic matter variability in the Early Silurian Qusaiba Source Rocks, Saudi Arabia. Retrieved April 08, 2021, from https://onepetro.org/SPEADIP/proceedings-abstract/17ADIP/2-17ADIP/D021S053R007/200216

5. Konert, Geert & Afifi, Abdulkader & Al-Hajri, Said & Droste, Henk. (2001). Paleozoic Stratigraphy and Hydrocarbon Habitat of the Arabian Plate. Geoarabia -Manama-. 6. 407-442.

6. Chan, S., Edigbue, P., Khan, S., Ashadi, A., & Al-Shuhail, A. (2021, February 04). Viscoelastic model and Synthetic seismic data of Eastern Rub'Al-Khali. Retrieved April 08, 2021, from https://www.mdpi.com/2076-3417/11/4/1401/htm

7. U. (2019). Rub Al Khali Basin Geologic Province 2019. Retrieved April 7, 2021, from https://certmapper.cr.usgs.gov/data/PubArchives/WEcont/regions/reg2/p2/P2019.pdf

8. U. (2019). Rub Al Khali Basin Geologic Province 2019. Retrieved April 7, 2021, from https://certmapper.cr.usgs.gov/data/PubArchives/WEcont/regions/reg2/p2/P2019.pdf

9. Aramco , saudi. “The Most Remote Treasure on Earth.” Aramco, Saudi Aramco Oil Company , 2021, www.aramco.com/en/who-we-are/mega-projects/shaybah.

External links

[1] [2] [3]