Owing to the U.S. shale boom, interest and activity in unconventional E&P has spread internationally.
Perhaps the most unexpected locale for these types of plays is the Kingdom of Saudi Arabia.
Given the enormous volumes of conventional production emanating from this hydrocarbon-rich region, it likely surprises many that unconventionals would hold any allure.
During the second EAGE/SPE/AAPG shale gas workshop in Dubai in 2014, a presentation attributed to four authors affiliated with Saudi Aramco reported that an accelerated unconventional exploration program had been launched in Saudi Arabia to develop unconventional hydrocarbon resources in various basins.
The unconventional gas plays evaluated were noted to run the gamut from rich to dry and are located in both the Rub Al-Khali and the Jafurah basins, among others. The targeted calcareous Jurassic sediments are deemed to be some of the richest hydrocarbon source rocks in the world.
Jafurah is east of Ghawar, which is the renowned supergiant oil field discovered in 1948. Accounting for more than half of Saudi Arabia’s cumulative oil production, the field also kicks out impressive volumes of gas.
It has long been recognized as the world’s largest conventional oil field, stretching 174 miles in length and 16 miles across to encompass 1.3 million acres.
The Jurassic-age Arab formation is a major oil reservoir in the Middle East, and the reservoir rock at Ghawar is the Jurassic Arab-D limestone having exceptional porosity. The Arab-D here includes the lowermost zone of the Arab and the uppermost zone of the Jubaila formation.
Some find it intriguing that the now-famous Cretaceous-age Eagle Ford shale in South Texas is a close analog to the Jurassic shale system in Saudi Arabia. For instance, the Jafurah and South Texas basins where the shales were deposited are both locally deprived of siliciclastic content and contain kerogen-rich, carbonate mudstone facies.
Jurassic carbonate reservoirs received vast amounts of oil from Jurassic carbonate source rocks within the Jurassic Tuwaiq Mountain, Hanifa and basal Jubaila formations, according to AAPG member Robert Lindsay, geological technical services at Saudi Aramco (retired), and his former colleagues. He has spoken on the topic at various meetings, including AAPG ACE 2015 in Denver.
The Jurassic source rocks contain 1-14 percent TOC, plentiful organopores and clay content quantity ranging from very low to none, according to Lindsay and his colleagues.
Deposition was in an outer ramp to basin depositions environment, beneath fair-weather wave base and within storm wave base.
He noted that a pycnocline, or the area where the density changes rapidly with depth, divided the water column into:
- Anoxic water beneath.
- Dysoxic water at the contact.
- Oxygenated water above.
He provided an outline of the Jafurah Basin unconventional lithofacies types occurring in order from shallow to deep:
- Evaporite strata – hypersaline.
- Bioturbated shallow marine strata – oxic.
- Bioturbated deep marine strata – oxic.
- Horizontally bioturbated deep marine strata – dysoxic.
- Laminated with starved ripples – anoxic.
- Laminated without apparent ripples – anoxic.
- Massive appearing very thin to thin– bedded strata – anoxic.
Additionally, Lindsay summarized the conclusions reached by the Jurassic source rocks study:
- A new play in Jurassic carbonate source rocks (in Jafurah).
- Source rocks filled Arab-D supergiant oil fields (such as Ghawar, Shaybah, Abqaiq, among others).
- Gas play is the size of Eagle Ford play in North America.
- Depositional model has been created connecting conventional and unconventional plays.
- Key lithofacies have been identified and tied to the depositional environment.
- Storms swept the ramp margin/basin and delivered TOC concentrated in fecal pellets into the basin.
- Porosity and permeability are elevated compared to the Eagle Ford.
If you’re hoping to be privy to the end results about this new play in the Jafurah Basin, patience is key.
“It’s still in appraisal mode,” Lindsay said.