Integrated Exploration Methods Applied to the Search for Natural Gas from Deeply Buried Coal Seams in Coos County, Oregon
George Hampton1, Steve Pappajohn1, Alan Niem2, Russell Ralls3, and Walt Johnson4
1 Methane Energy Corporation, TX
2 Pacific Northwest Geology
3 North Oregon Resources
4 Exploration GeoConsultants Inc.
Exploration for natural gas reserves contained in deeply buried coal seams is currently being conducted in Coos County, Oregon. The Coos Bay basin is delineated by the coal-bearing outcrops of the Eocene age Coaledo Formation. Integrated exploration methods include: review of past drilling and coal mining history, a continuous coring and gas desorption sampling program, proximate and isotopic gas analyses, use of re-processed seismic lines, construction of isopach and structural contour maps and creation of detailed geologic maps and cross sections.
The coal-bearing Coaledo Formation is 6,600 feet thick and contains multiple coal seams, many of which are saturated with natural gas. Coal beds are found in both the upper and lower Coaledo Formation. The basin is relatively unexplored in regards to hydrocarbons and less than 20 wells have been drilled in the basin since 1900. Many gas shows were logged, but largely ignored.
Two (2) coal seam natural gas exploration wells were drilled in the Coos Bay basin in 1993 and significant gas shows were encountered in the coals. Gas desorption values from the 2 wells drilled in 1993 resulted in gas contents ranging from about 100 to 250 SCF/T. Gas analysis yielded nearly pure methane (93-99%) with Btu values (940-1000).
Methane Energy Corporation (MEC) drilled a 5-well information hole program that was completed in May 2005. Measured gas contents confirmed the original 1993 measurements. Gas composition was nearly pure methane (98 %+). Isotopic gas analysis classifies the desorbed gas as decidedly thermogenic (∂13C ≈ -30‰). Two five-well pilot projects were drilled in 2005-2006. A gas in-place (GIP) resource base of over 1.6 trillion cubic feet has been estimated within the Coos Bay basin. This compares favorably to existing CBM fields elsewhere in North America.