Steam-cleaning heavy crude

Sept. 25, 2006
Steam injection is effective for increasing recovery from subsurface heavy crude or bitumen accumulations.

Steam injection is effective for increasing recovery from subsurface heavy crude or bitumen accumulations. Some projects do produce these resources with cold production, but recovery expectations are low, in the range of 5-10% of initial oil in place. With steam injection, recoveries in some projects may exceed 70%.

As discussed in the lead article in the Production Report, p. 39, the next decade will have a host of new steam projects starting in Alberta that will contribute greatly to the province’s plans for exploiting its estimated 174 billion bbl of heavy-oil resource out of the 1.69 trillion bbl in place.

But Alberta is not alone in having large heavy crude accumulations. These resources are found in many regions of the world, including Venezuela, China, Indonesia, India, the Middle East, Brazil, Albania, Russia, the North Slope of Alaska, California, and Texas.

Heavy crudes

The definition of heavy and extra-heavy crude oil and bitumen varies but usually says that it is a petroleum or petroleum-like liquid or semisolid occurring naturally in porous and fractured formations. Other names for bitumen deposits include tar sand, oil sand, oil-impregnated rock, and bituminous sand.

Viscosity and density usually characterize the substance.

Viscosity differentiates between crude and bitumen, while density differentiates extra-heavy, heavy, and other crudes.

Bitumens have viscosities greater than 10,000 cp. Crude oils have viscosities less than or equal to 10,000 cp. These are gas-free viscosities, measured at the original reservoir temperature.

Extra-heavy crude has API gravities less than 10°, while heavy crude gravity varies from 10° to 20° at 60° F. and atmospheric pressure.

Steam injection

Steam-assisted gravity drainage (SAGD), which uses parallel horizontal wells such as are planned for many projects in Alberta, is relatively new. Other projects in Alberta, such as at Imperial Oil Ltd.’s project at Cold Lake, produce with a cyclic steam process, in which the same well is both the injector and producer. Production from Cold Lake is increasing and currently is about 140,000 bo/d.

The use of steam for recovering heavy crude started in the 1960s in Venezuela and California. Cyclic steam injection was the initial process used, although many projects, especially in California, were converted to steamfloods with dedicated injection and producing wells. California still produces about 280,000 bo/d from steam projects, although this is down from the peak in the mid-1980s of about 480,000 bo/d. Steam has enabled the recovery of several billion barrels of crude from the San Joaquin basin in California.

Chevron Corp., one of the major steamflood operators in California, sees production from its properties continuing to decline-although at 2%/year compared with the 4%/year declines experienced in recent years.

A unit of Chevron also operates the largest steamflood in the world in the Duri field in Indonesia. Current production is about 200,000 bo/d, compared with a peak of about 300,000 bo/d in the mid-1990s. Prior to the 1985 start of steamflooding in Duri, the field produced about 30,000 bo/d.

Although production in Duri continues to decline, Chevron is initiating a steamflood in North Duri. It expects production in North Duri to peak at 35,000 bo/d after the start-up in 2008.

Chevron also is expanding its pilot steamflood in the Partitioned Neutral Zone between Kuwait and Saudi Arabia.

Another new steamflood in the Middle East is in the Mukhaiza field, Oman. Occidental Petroleum Corp. plans for steam injection to start in 2006. The $3 billion project may include more than 1,800 wells and has a target production of 150,000 bo/d in 2011.

Bankers Petroleum Ltd., Calgary, is redeveloping the giant Patos-Marinza heavy oil field in central Albania and has started studying the potential for injecting steam for increasing the recovery factor of the 2 billion bbl originally in place above the 10% expected under cold production.

Patos-Marinza was discovered in 1928 and placed on production in 1939.

The Exploration Co. in August started injecting steam in two wells in the Maverick basin of South Texas. Its San Miguel heavy oil field project targets the recovery of some of the 7-10 billion bbl of heavy oil estimated to reside in the basin.

Although steam generation adds costs, it is essential for cleaning out a greater amount of the heavy crudes found in many of the world’s sedimentary basins.