NATURAL GAS FROM TERTIARY-AGE COALBEDS IN THE PACIFIC NORTHWEST: RENEWED OPPORTUNITIES FOR ENVIRONMENTALLY FAVORABLE ENERGY OPTIONS FROM COOS COUNTY, OREGON

A favorable nexus of an identified resource base, rapidly advancing natural gas production technologies, proximity to pipeline transportation, and public support is renewing interest in environmentally-preferred natural gas resources in the Pacific Northwest. Exploration for natural gas from coal seams has been conducted in the PNW region since 1980. Middle-Late Eocene age deltaic sediments, deposited on an extensive subtropical swampy coastal plain, have been preserved in the Puget-Willamette trough from British Columbia south along the west flank of the Cascade Range. The Coos Bay basin located on the Pacific Coast in southwestern Oregon is the southernmost representation of these prospective natural gas-bearing sediments.

Situated along the western convergent margin of the North American tectonic plate, the Coos Bay basin is delineated by the coal-bearing outcrops of the upper-middle Eocene age (approx. 40 mybp ) Coaledo Formation. The coal-bearing sandstones and siltstones of the Coaledo Formation are estimated to form a section approximately 6,600 feet thick. A robust coal mining industry existed in Coos County in the late 19th- through the early 20th-century.

Integrated exploration methods include review of past drilling and coal mining history. Drilling data from core holes, a continuous coring and gas desorption sampling program, coal rank, and isotopic gas analyses were also employed. Included were use of re-processed seismic lines, construction of isopach and structural maps, creation of detailed geologic maps and cross- sections (including using backhoe to expose outcrops and trenches in this thickly forested area), and outcrop, core, and image logs.

The Coaledo Formation contains multiple seams of coal, many of which contain natural gas. A comprehensive study conducted by Sproule & Associates assigns an in-place resource of 1.2 TCF of gas in the basin. The latest round of exploration drilling (mid- 2000’s) and testing of coalbed methane production pre-date the recent advances in horizontal drilling, formation stimulation technologies, and other production innovations available today. A pipeline has been constructed with the basin to serve the local community. Interest in and support of a large LNG facility at Coos Bay is also positive for the continued natural resource exploration in the area.