It’s a given that the many giant oil fields in the Middle East harbor immense volumes of crude oil – principally the highly prized light, sweet kind.
In fact, this region might best be dubbed the light oil capital of the world.
Perhaps this accounts for the fact that the heavy oil resource there has been overlooked in large part.
Estimates of this resource base vary considerably.
For example, Schlumberger and the U.S. Geological Survey estimate heavy oil resources to be 500 Bbo and 971 Bbo, respectively, according to AAPG member John Buza, senior advisory geologist at Chevron Corp.
He noted, however, that both available proprietary databases and published data for certain fields suggest a much lower stock tank original-oil-in-place resource base of perhaps 120 Bbo.
Buza presented a paper titled “An Overview of Heavy Oil Carbonate Reservoirs in the Middle East” at the recent AAPG Annual Convention and Exhibition in New Orleans.
Relatively little heavy oil is being produced currently in this region, but the resource has the potential to replace or increase production overall to some extent should the global demand/supply situation justify this scenario. Ultimate recovery from the heavy oil fields depends on oil viscosity and the ability to lower it.
The copious quantities of light oil in the Middle East are found in carbonate reservoirs for the most part. Heavy oil is no exception.
Buza, commenting prior to the New Orleans convention, noted heavy oil carbonate fields in the region produce via two different mechanisms. The more dominant is low matrix permeability, fracture dependent production, found in producing fields such as Qarn Alam in Oman and Issaran and Bakr-Amer in Egypt.
These type reservoirs can cause operators to quaff their daily max of headache meds.
“Owing to their low matrix porosity and permeability and complex distribution of fractures, fractured heavy oil reservoirs are one of the most difficult and heterogeneous reservoir types to develop,” Buza said.
“Reservoir quality and heterogeneity vary from one reservoir type to another,” he noted. “The highly variable porosity distribution and uncertainty in fracture density and quality make definition and delineation of net reservoir thickness nearly impossible.”
The Bottom Line
The other category of heavy oil carbonate field production is matrix permeability-dependent production.
The Wafra heavy oil field in the Partitioned Neutral Zone of Kuwait and Saudi Arabia is a significant example of a field having sufficient matrix permeability to enable economic cold production – i.e., no heat injected into the reservoir – without substantial fracture enhancement.
Steam injection pilot studies are ongoing at Wafra, which produces in the neighborhood of 86 thousand barrels a day (TBD) of heavy oil. This provides more than half of the approximately 150 TBD of current heavy oil production from carbonate rocks in the Middle East, which accounts for 0.5 percent of total oil production in the region.
Both steam and CO2 EOR projects have been implemented in various heavy oil reservoirs in this part of the world.
“These have both proved effective in increasing EUR,” Buza said. “But it’s met with varying degrees of success, depending on rock fabric and even more importantly on the initial viscosity of the oil and the capability to lower it.
“Actually, bona fide heavy oil carbonate reservoirs (<22 degree API gravity) represent modest future production for the Middle East region compared to the current production and substantial EUR from conventional light oil reservoirs,” Buza emphasized.
“The whole theme of why people are looking at this resource is that obviously the light oil, the cheap oil is becoming scarce everywhere,” he said. “That’s the bottom line why this is going on.
“People wouldn’t give you the time of day 10 years ago if you were trying to peddle this heavy stuff,” Buza emphasized. “But today, we’re running lean on the easy-to-get kind.”