Operators' stellar performance in more than replacing US production in 2001 revealed some interesting differences with respect to gaseous and liquid hydrocarbons.
The US Department of Energy's Energy Information Administration reported increases of 3.4% for dry natural gas reserves and 1.8% for crude oil in 2001 (OGJ Online, Sept. 30, 2002).
A single deepwater discovery in the Gulf of Mexico accounted for a "significant portion" of the oil reserves added, EIA noted, while the increased gas reserves are in challenging, low-permeability reservoirs spread across three states.
The gas reserve additions are mostly onshore and include a serious contribution from coalbed methane (CBM).
The oil reserves are largely in the BP PLC-operated Thunder Horse discovery in more than 6,000 ft of water in the Mississippi Canyon area, expected to become the gulf's largest field.
The net of reserves revisions and adjustments—as much as 54% of annual crude oil reserves additions in past years—was a very small component, a downward shift of 162 million bbl, in 2001.
Finding patterns
The existence of 300-400 giant and supergiant oil fields has buoyed US oil reserves in the past, and many of those fields still contribute significantly to production.
The newest giant, Thunder Horse, with upwards of 1.5 billion boe of reserves, accounted for a big share of the 1.7 billion bbl of new field and new pool oil reserves added in 2001. It will be tapped with a facility designed for a peak 250,000 b/d of oil and 200 MMcfd of gas (OGJ Online, Nov. 5, 2001). Only a few dozen wells are needed.
That's not the case in the fields where the 2001 gas reserves were added, which involved the drilling of hundreds or thousands of wells.
Operators added 3.5 tcf of gas in new field discoveries and 2.8 tcf in new pools in 2001. The majority of proved gas reserve additions came in Pinedale field in Wyoming, the Lobo trend in South Texas, Barnett shale fields in North Texas, and Wattenberg field in Colorado.
Natural gas liquids reserves usually increase with gas reserves but didn't in 2001. That was because CBM, which effectively has no natural gas liquids content, made up a large portion of the gas reserves increase.
Coalbed methane
Significant CBM reserves were added in the Powder River basin in Wyoming and in fields in Colorado.
CBM reserves in the US were 17.5 tcf at the end of 2001, up from 15.7 tcf at the end of 2000 and 8.2 tcf at the end of 1991. EIA reported CBM reserves and production in 11 states. The five largest CBM reserves by state are those in Colorado 6.3 tcf, New Mexico 4.3 tcf, Wyoming 2.3 tcf, Utah 1.7 tcf, and Alabama 1.2 tcf.
For 2001, CBM production was 1.6 tcf, including 517 bcf from New Mexico, 490 bcf from Colorado, 278 bcf from Wyoming, 111 bcf from Alabama, and 83 bcf from Utah.
EIA also listed CBM reserves and production in Pennsylvania, Virginia, West Virginia, Kansas, Montana, and Oklahoma.
Almost all of the state changes in reserves and production were positive compared with the end of 2000.
