THE U.S. GEOLOGICAL SURVEY GEOLOGIC CARBON SEQUESTRATION ASSESSMENT PROJECT: UNCONVENTIONAL RESERVOIRS WORKSHOP

In March 2012, the U.S. Geological Survey (USGS) held a workshop entitled “CO₂ Sequestration in Unconventional Reservoirs”, with 36 participants from academia, industry, and government. The goals of the workshop were to: 1) determine the current state of laboratory, modeling, and pilot projects in unconventional reservoirs; 2) discuss the feasibility of CO₂ storage in unconventional reservoirs; and 3) build a set of recommendations that could be used to underpin a USGS methodology to assess CO₂ storage potential in unconventional reservoirs, if such storage proves feasible. The workshop participants participated in two working groups to address CO₂ sequestration issues in: 1) coal and organic-rich shale and 2) basalt and ultramafic rocks. The results of this workshop are described below from the coal and organic-rich shale working group.

The coal and organic-rich shale working group addressed the feasibility of long-term CO₂ storage primarily by sorption, and reviewed several current pilot projects involving CO₂ injection into coal and organic-rich shale. The group produced several recommendations regarding a potential CO₂ storage assessment methodology including: 1) coal and organic-rich shale should be assessed separately from each other, although their mechanisms for CO₂ storage are similar, and 2) storage potential should be assessed in all coal beds rather than only in “unmineable” coal, since coal mineability depends on changeable economics and technology, rather than on geologic characteristics. Many other factors were considered important in the development of a methodology to understand CO₂ storage potential in coal and organic-rich shale formations, including, 1) enhanced gas or oil recovery using CO₂ injection, and 2) matrix swelling with a corresponding decrease of permeability and injectivity as a result of CO₂ injection.

At the end of the workshop, the participants recommended that the USGS proceed with development of a methodology for assessment of CO₂ storage potential in coal and organic-rich shale reservoirs.