Piceance basin oil-shale study finds 1.5 trillion bbl in place

Aug. 30, 2010
An estimated 1.5 trillion bbl of oil in place lies in Western Colorado's Piceance basin oil shale, the US Geological Survey said in the first comprehensive assessment published since 1989.

An estimated 1.5 trillion bbl of oil in place lies in Western Colorado's Piceance basin oil shale, the US Geological Survey said in the first comprehensive assessment published since 1989. The amount represents a 50% jump from the previous 1 trillion bbl of oil in place estimate because about twice as many oil yield data points were used, USGS added in a new report.

Even at the previous 1 trillion bbl estimate, the Piceance represented the largest oil shale deposit in the world.

"Almost all of this increase is due to (1) new areas being assessed that had too little data in the previous assessment, and (2) new intervals being assessed that were not assessed previously," it said. Much of the previously unassessed resource is low-grade and unlikely to be developed, the report added.

The Piceance basin is one of three large western US basins that contain significant oil shale resources. The Uinta basin, in eastern Utah and westernmost Colorado, and the Greater Green River basin, in southwestern Wyoming, northeastern Utah, and northwestern Colorado, also contain large amounts, and will be assessed separately, USGS said.

The report noted that a considerable amount of data was collected after the previous Piceance basin assessment, and the information has been incorporated into the new one where 2,178 data points were used, compared with 1,083 in the earlier study. "Much of this additional data was donated by private industry after interest in developing oil shale waned in the 1980s," it said. The latest assessment also includes five oil shale intervals that were not part of its predecessor, it added.

Inaccessible data

The effort was hampered by difficulties recovering digital files used in previous assessments by USGS and the former US Bureau of Mines (USBM), which was disbanded in 1996, according to the report. Much of the USGS data was stored on outdated digital mediums that either degraded to a point that they could no longer be read, or a suitable computer or software which could read the data could not be found, it explained.

The considerable amount of data stored on USBM computers is presently not accessible, the report said. "In many cases, only computer printouts of the data remained that had to be scanned and tediously rectified," it indicated.

There also have been considerable advances in computational power and computer programs since the previous assessment was published, and the new one tries to take full advantage of these improvements, the report continued. But the new report does not try to estimate the amount of oil recoverable from the shales, it emphasized.

It cited a recent Rand Corp. report, which observed that recoverable resource estimates are usually based on an analysis of the resources in place which can be economically exploited with available technology.

'Rough estimates'

"Because oil shale production has not been profitable in the United States, such estimates do not yield useful information," the Rand report said. "Instead, calculations of recoverable resources have generally been based on rough estimates of the fraction of the resources in place that can be accessed and recovered, considering mining methods and processing losses."

Previous estimates of the amount of oil technically recoverable from the Piceance basin's oil shale formations without considering economics, and using the room and pillar method, ran from 45% in a 1987 study to 55-75% in a 1974 study, the new USGS report said. Estimates in the 1987 study of the technically recoverable oil climbed to 80% when open pit mining was used, it added.

There currently are no estimates of the amount of the Piceance basin's oil shale resource that could be recovered using as yet undeveloped in-situ methods, the report said. The 1987 study it cited stressed that the amount using these processes would depend on both the percent of the oil which could be recovered from within the retort, and the amount of oil left behind in areas between the retorts, it indicated.

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