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Advanced Technology Brings California Oilfield Back to Life  
Date: April-04-2001

An abandoned Bakersfield, California oil lease, brought back to life in 1995 by a joint government-industry experimental project, has produced more than a million bbl of oil once thought unrecoverable.

Because of the success, oil is now flowing from 100 new, privately funded wells in the immediate vicinity, and experts predict that the advanced technologies demonstrated in the federally co-funded field test could lead to millions more bbl of oil recovered from fields around the Bakersfield area.

"This is oil from a US field that otherwise would have remained beyond the reach of conventional technologies," said Secretary of Energy Spencer Abraham. "The Energy Department is committed to making successes like this become more commonplace. Clearly, new technologies and advances in oil exploration and production techniques contributed to the successful recovery of oil that would otherwise be unreachable with conventional technologies."

The project took place on the Pru Fee lease, part of the giant Midway-Sunset Field roughly 30 miles southwest of Bakersfield. Support from the US Department of Energy, in coordination with the University of Utah, Aera Energy LLC, and ARCO Western Energy, made testing of the improved technologies possible when normal commercial practices were no longer effective.

In the last five years, the million bbl of "new" oil that has flowed from the field is more than half as much oil as the property produced in all of its first 80 years of operation. Project sponsors predict that the advanced technologies ultimately will result in more than 4 million bbl of oil being produced—all from a 40-acre property once thought to be dead from an oil producer's perspective.

The project is one of several supported by the Energy Department in its Reservoir Class Oil Field Recovery Program. Begun in 1991, the program targeted geologic classes of US oil fields that were on the verge of being prematurely abandoned. With federal matching funds allowing higher-risk technologies to be tried, many operators have been able to keep oil flowing from these fields long after conventional wisdom labeled them "depleted."

The Pru Fee project in the Midway-Sunset Field was selected in the third round of the program in 1995. The Energy Department provided US$2.2 million, and the University of Utah and its industry partners contributed $3.6 million.

Discovered in 1894, the Midway-Sunset Field was booming by the early 1900s.

The Pru lease was a major part of the early oil surge, coming into production in 1906. But by the late 1960s, output from the lease had dropped off greatly, and operators began injecting steam to thin the heavy oil in an attempt to keep it flowing.

The technique worked for a while—the field was producing 300 b/d in1972—but by 1985, production had dropped to less than 10 b/d. The lease was abandoned. But there was tantalizing evidence that as much as 90% of the property's oil remained behind. Other Midway-Sunset tracts continued to produce, but oil trapped in the 200- to 300-ft-thick sand formation beneath the Pru lease seemed beyond the capabilities of conventional technology.

Using modern advances, engineers ran seismic surveys, compiled new information on rock properties, and analyzed cores and outcrops to create a geologic profile of the reservoir in unprecedented detail. They fed the data into advanced computer programs that simulated how the reservoir would respond to various production strategies. The computer helped pinpoint the optimal patterns where new wells should be drilled to inject steam and recover the most oil.

Initially, ARCO Western evaluated the previously tried technique of "cyclic steam flooding", using an 8-acre section of the lease to alternately inject steam, then recover oil. But after two steam cycles, production dropped off.

The research team then turned to continuous steam injection, sending a steady flow of steam down one set of wells and recovering oil from other wells. Production picked up and stayed up, eventually reaching more than 1,500 b/d.

By early 1999, 37 new wells on the lease had been put on line. Aera Energy (jointly owned by Shell and ExxonMobil), which acquired the lease from ARCO, began applying the technologies to leases surrounding the Pru Field. Currently 54 new wells have been placed into production, the most recent at the Lilly lease, which is twice as large as Pru and could hold up to 10 million bbl of recoverable oil.

The Energy Department's National Petroleum Technology Office, which oversaw the project, now estimates that applying the new methods to only half the 26 currently shut-in Midway-Sunset properties could produce another 80 million bbl of oil. The federal taxes on this oil alone would total more $10 million, nearly five times the government's original investment in the Pru Fee project.

 

Author: Source: US Dept of Energy

 

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