 | |
| Last: |
$0.31 |
| Volume: |
3750 |
| Change: |
-0.05 |
| Date: |
12-03-2008 |
| Time: |
15:35 |
15-20 min delay
| |
Our Columbia Basin property underlies the widespread Miocene Columbia River Basalt group in east-central Washington. We believe, Washington is a petroleum exploration frontier, and several possible gas systems may be present. "There is no current production in Washington, however, the region has been considered a petroleum frontier since 1990 when the States first wildcat well was drilled in Snohomish County." USGS Professional Paper 1582 (Lingley, Law, et al.'s paper)
An analysis of the Columbia Basin published in USGS Professional Paper 1582 suggests there is a basin-centered gas accumulation below the basalt group, which is of variable thickness up to 1,524 metres (5,000 ft). Interpretation of subsurface data indicates that the top of the thick, over pressured interval begins at depths ranging from 2,530 to 3,872 metres (8,300 to 12,700 feet), and within the large interval large amounts of gas may exist.
The Columbia Basin, is also known as the Columbia Plateau, is a vast area in south-eastern Washington,. The physiographic province is characterized by incised rivers, extensive plateaus, and anticlinal ridges rising to 4,000 feet above sea level. The region is underlain by Miocene Columbia River Basalt Group rocks and interbedded Neogene terrestrial sediments.
Data about what lies under the Columbia River basalts is sparse. Along the Idaho border south of Spokane, steptoes that once were mountain tops consist of Precambrian Belt Supergroup sedimentary rocks and metamorphosed Cretaceous granites. These mountains were enveloped by Miocene basalts so that only the summits remain above the lava flows. Deeply weathered granites support a clay mining industry, and a cassiterite deposit is known just south of Spokane.
Even less is known about the pre-Miocene basement in the central and western parts of the Columbia Basin. The only information available is from seven petroleum exploration wells that have penetrated the basalt and from projections of geology from the margins of the basin. Along the margins, Paleogene fault-bounded basins are filled with thick sequences of arkose, volcaniclastic rocks, and coal. Drilling has demonstrated that in a general way these sedimentary basins extend southward under the Columbia River basalts. The subsurface geology changes as one reaches the Snake River. A 1987 exploratory well drilled 20 miles northeast of Pasco penetrated a thin Paleogene crystal tuff section before encountering Triassic or Jurassic chloritic metamorphic rocks at an approximate depth of 8,000 feet.
The Columbia basin province is best defined by the areal extent of the Miocene Columbia River Basalt Group rocks. These basalts, which are present in the Blue Mountain uplift as well as in the Columbia Basin, cover 36 percent of the entire state. The group consists of four flood basalt formations, starting with the Imnaha Basalt at 17.5 Ma, followed by the Grande Ronde Basalt (16.5 to 15.6 Ma), the Wanapum Basalt (15.6 to 14.5 Ma), and lastly the Saddle Mountains Basalt (14.5 to 6 Ma). On the basis of geophysical evidence, the basalts are known to reach a maximum thickness of 16,000 feet in the Pasco Basin. An exploratory gas well (BN 1-9) drilled southeast of Vantage penetrated 11,500 feet of these basalts before entering Paleogene sediments. The Columbia Basin province is modest in size in comparison with other continental flood basalts such as the Deccan basalts of India; however, the basin has been studied in greater detail than any other such basalt accumulation in the world. This is true because the basalts were once seriously considered for deep geologic disposal of the nation's high-level nuclear waste.
The four formations of the Columbia River Basalt Group consist of 38 units or members that in the three-state area (Washington, Idaho, and Oregon), cover 63,208 square miles (163,700 km2), and have a volume of 41,820 cubic miles (174,300 km³). The greatest volume of basalts was erupted before 15.5 Ma. These flows have similar appearances; techniques have been developed, however, to fingerprint individual basalt units using whole-rock geochemistry and magnetic polarity. Within the Grande Ronde Basalt, individual flows exceed 480 cubic miles (2,000 km³) in volume. The flows were extruded from vents and northwest-trending fissures east of Pasco and in the southeast corner of the state. The flows were extremely fluid, and as a result a number of them reached the Pacific Ocean via the ancestral Columbia River drainage.
There were periods of quiescence between major extrusive events. Erosion would take place, and tuffs, sandstones, and conglomerates would be deposited on top of basalt flows. In some areas, lake beds formed. Forests developed during these periods. Another basalt flow would follow, infilling canyons, engulfing trees, and covering lake sediments. These sedimentary horizons have such names as the Latah Formation (near Spokane), the Vantage Interbed with its opalized and silicified wood, and the Ellensburg Formation consisting of volcaniclastics shed from the growing Cascades. The state is a major producer of diatomite from lake beds that were covered by flows. Ginkgo Petrified Forest State Park is an excellent place to view petrified trees. In 1975, the state legislature designated petrified wood as the state gem.
In the western portion of the Columbia Basin, the flows of the Columbia River Basalt Group have been folded into a series of giant anticlines that strike east-west to southeast-northwest. This region is called the Yakima Fold Belt subprovince. The anticlines have steep dips north of the fold axis and overturned beds in numerous locations. The south flanks of the anticlines have gentle dips. Folding was initiated during middle to late Miocene time and has continued to this day. Crossing the Columbia Basin is a northwest-trending tectonic feature called the Olympic Wallowa Lineament. Right-lateral displacement on this transform structure influenced the formation of the Pasco Basin.
The Rattlesnake Hills anticline produced 1.3 billion cubic feet of natural gas from the Columbia River Basalt Group during the years 1929-1941. The state drilling depth record was reached by well BN 1-9 on the Saddle Mountains anticline with a total depth of 17,518 feet. It took from 1982 to 1984 to drill and test the well. This well encountered considerable natural gas but not enough to make production profitable.
The above text is modified from the following article: Lasmanis, Raymond, 1991, The geology of Washington: Rocks and Minerals, v. 66, no. 4, p. 262-277. (c) Copyright Heldref Publications (Helen Dwight Reid Educational Foundation).
| | | |
