Wednesday, September 14, 2011
Musings: Trying To Solve Mystery Of Missing Marcellus Resource
The recent assessment by the U.S. Geological Survey (USGS) that the Marcellus Shale contains 84 trillion cubic feet (Tcf) of undiscovered natural gas and 3.4 billion barrels of undiscovered natural gas liquids was greeted with both joy and consternation. The joy came from the recognition that the USGS estimate was a huge increase from its prior assessment made in 2002 that said there was only about 2 Tcf of gas reserves in the shale formation that stretches from Alabama to New York.
The consternation stems from the assessment being about 80% less than an estimate promoted earlier this year by the Energy Information Administration (EIA) that there was 410 Tcf of gas in the basin. Talk about a gap wide enough to drive a truck through, how about a whole fleet of pickups?
First, it is important to understand that the USGS estimate is the mean of various estimates the agency prepared. Each estimate was assigned a confidence level based on how sure the agency was that the estimated volume actually is present. The estimates ranged from a very highly confident (95%) estimate of 43 Tcf to the estimate with the lowest confidence (5%) of 144 Tcf. The 50% confidence scenario estimated total gas reserves of 78.7 Tcf, or somewhat below the mean estimate the agency decided to publish.
Second, it is important to understand that these estimates reflect a view that the resources are technically recoverable, which, to quote from the agency's press release, means "are those quantities of oil and gas producible using currently available technology and industry practices, regardless of economic or accessibility considerations." The USGS went on to say, "…these estimates include resources beneath both onshore and offshore areas (such as Lake Erie) and beneath areas where accessibility may be limited by policy and regulations imposed by land managers and regulatory agencies."
Importantly, the USGS attributed the increase in its undiscovered resource estimate to the "new geologic information and engineering data, as technological developments in producing unconventional resources have been significant in the last decade." Clearly, the USGS was referring to the improvements in horizontal drilling and hydraulic fracturing, which the petroleum industry has embraced wholeheartedly in driving the gas shale revolution......Read the entire article.