Study of Viability of Seismic Imaging for Site Selection and Monitoring of CO2

Iraj A. Salehi, Sherif I. Gowelly, and Samih I. Batarseh
Gas Technology Institute, Des Plaines, IL

In this paper, we present results of a series of field and laboratory experiments aimed at determination of seismic resolution relative to thin Illinois coal seams and study of viability of time-lapsed seismic imaging (4-D seismic) for monitoring the position of the injected carbon dioxide front during CO2 sequestration process, or desorbed methane in the case of coalbed methane production. The project was a cooperative effort between Illinois Clean Coal Institute (ICCI) and Gas Technology Institute (GTI) with valuable technical contribution and logistical support from Illinois State Geological Survey (ISGS).

Illinois coal seams are shallow and thin with the thickness rarely exceeding 10 feet. To investigate viability of seismic technology relative to imaging of Illinois coal seams a series of seismic data acquisitions including surface seismic, vertical seismic profiling, and crosswell seismic imaging carried out at the ISGS pilot site in Southern Illinois. Results were encouraging in that the data proved that thin coal seams can be reliably mapped by properly designed seismic surveys.

Our second objective was to verify viability of 4-D seismic as a monitoring tool for the potential CO2 sequestration projects in coal seams of Illinois. In pursuing this objective, a number of elaborate laboratory measurements of acoustic velocity in gas and water saturated coal samples were carried out. Results of these measurements showed that the magnitude of velocity change resulting from addition of a gas phase into water saturated coal samples is large enough to render the time-lapsed seismic technique useful for monitoring the position of injected or evolved gas fronts.