The goal is to develop alternatives for natural gas storage in market areas where conventional storage options may be technically unfeasible.
Pacific Northwest National Laboratory (PNNL)
Increasing demand for natural gas in the Pacific Northwest will require development of new storage facilities. Geologic storage is one option, provided adequate capacity and containment requirements can be met in favorable locations. Extensive areas of thick layers of basalt within central Washington State represent a relatively unexplored alternative for subsurface gas storage. The layered basalts of this area are typically very dense, but the rapidly cooled upper portions of each flow are commonly very porous. Small volumes of natural gas were produced from these porous basalt layers in the early part of the century and they could have potential for storage. The challenge is to identify specific locations that are both suitable for storage and near existing pipelines. This project completed a preliminary screening assessment and a compilation of the information and methods needed to select and characterize suitable locations for subsurface gas storage within the deep basalts of the Columbia Basin.
In general, the research found that the deeper basalt aquifers in the central portion of the Columbia Basin are suitable for subsurface storage. There is sufficient thickness of basalt for natural gas storage and high hydrostatic pressures for gas containment. The total thickness of the basalt (>5 km) is greatest in this area. There are also numerous anticlines (Yakima Fold Belt) that can provide geologic closure. This increases the likelihood of locating a suitable structure for closure or containment of injected gas. Earthquake activity is minimal and groundwater quality in potential storage horizons precludes their use for domestic purposes. In addition, the groundwater flow rates are very low, meaning that dissolved gas would migrate advectively at very slow rates.
A large subsurface characterization database exists for the geology and hydrology of the central Columbia Basin. Studies over the years by the U.S. Department of Energy (DOE) have provided regional geology and deep basalt and aquifer characterization data. These data allow preliminary site screening for areas with the greatest likelihood of vertical hydrologic isolation (caprock/containment).
Natural gas pipelines run southeast to northwest through the center of the Yakima Fold Belt and along the southern boundary. In addition, a natural gas transmission line runs north to south across the eastern part of the Columbia Basin. The occurrence of a commercial gas field along the western margin of the Pasco Basin (Rattlesnake Ridge) that was exploited until the 1940s provides evidence that basalt interflow zones can serve as natural gas storage reservoirs. Finally, much of the land within the central Columbia Basin is already removed from the private sector (e.g., Hanford Site). Thus, developing a natural gas storage project on federal land would avoid the need to acquire privately held land.
Determine the feasibility of storing natural gas in multi-layered basalts in the Pacific Northwest, and develop assessment protocols for selecting suitable sites.
Collectively, the Columbia River Basalt Group (CRBG) covers an extensive area with individual lava flows covering many tens of thousands of square kilometers. The great volume and extent of CRBG lava flows sets them apart from typical small-size lava flows and provides attractive targets for gas storage reservoirs. Although only the interflow zones are usable for natural gas storage, the great volume and extent of CRBG flows put them on equal footing with sedimentary formations that are currently being used for gas storage. Scoping calculations indicate that a single interflow zone (at a depth of 1,000 m) in an anticlinal basalt structure 1 to 2 km wide 5 to 10 km long can provide more than adequate storage space for a typical 0.4 billion cubic meter facility. Larger storage volumes could be achieved by using multiple interflow zones at an individual storage site location.
Much of the background information developed for this project is equally applicable to both gas storage and carbon dioxide disposal. Various schemes to sequester this greenhouse gas have been proposed, including geologic disposal. Injection into deep basalt aquifers involves many of the same considerations as required for natural gas storage. Chemical reactions unique to basalt may enhance retention of the carbon dioxide as carbonate solid phases. In addition, a structural trap to restrict lateral movement of the injected gas is not required, making larger areas available for sequestration. Thus, this option is an alternative to other modes of off-gas treatment for fossil-fired power plants located in the Columbia Basin.
This project has been completed and a final report is available (PNNL-13962).