DoReMi-A Passive Geophysical Monitoring Technique for CO2 Injection

The carbon dioxide (CO2) injection at the Citronelle Oil Field in Alabama has been deployed since December 2009. The injection of the first 7,500 tons of CO2 has been completed in September 2010. To monitor the CO2 injection process and determine the potential for geological changes that may occur because of the injection, geophysical testing has been used at the site: a Derivative of Refractive Microtremor (DoReMi) method using wireless sensor has been conducted for acquiring ground motion in October 2008, January 2009 and June 2009, prior to injection, and again in December 2009, March 2010, May 2010 and September 2010, during injection, and after injection in November 2010, March 2011 and May 2011. The measurements were made at well sites along two linear arrays running from north - south and from northeast - southwest. The outcomes of the geophysical monitoring at the Citronelle Oil Field are shear-wave velocity profiles that are correlated to the static stress distribution at different injection stages. It is noticed that the pressure in the oil production layer and overburden strata at the time of water injection and CO2 injection has already built up in the entire monitored region. The results of the geophysical monitoring for the pilot injection will aid oil field operators in decision making for the future commercial-scale reservoir management strategies.