Interpretation of CO2 Saturations in the Aquistore Observation Well using Pulsed Neutron Logs

  • Technical Session Five: Carbon Capture and Storage
  • May 29, 2019
  • 11:45 am - 12:15 pm

WBPC 2019 Abstract #18:

Co-Author: Ghulam Sohail, University of Saskatchewan

At the site of the Aquistore Project near Estevan, Saskatchewan, CO2 is injected into brine-saturated Cambro-Ordovician sandstones overlying Precambrian basement rocks for the purpose of CO2 storage. Injection began in April, 2015, using a single vertical injection well which is perforated over intervals ranging from 3175 to 3365 m depth. This paper describes the use of time-lapsed pulsed neutron logging which was undertaken to detect the arrival of CO2 at the project’s observation well, which is located approximately 150 m from the injection well. The observation well transects the injection zone but contains no perforations. Pulsed neutron logging was chosen as part of the project’s measurement, monitoring and verification program, as this technology has proven effective elsewhere for detecting CO2 through casing. A total of 21 pulsed neutron logging runs have been made in the observation well (17 using Weatherford’s PND tool and 4 using Schlumberger’s RST tool) from dates prior to CO2 injection through to April, 2018. Statistically-significant changes in log response have been observed from February, 2016 onwards. The most notable CO2-bearing zone is an interval approximately 6 m thick in the upper part of the Deadwood Formation, with CO2 saturations in the 0.4 to 0.6 range. The second most notable interval is approximately 2 m thick and is near the base of the Black Island Member of the Winnipeg Formation. The results obtained using both pulsed neutron tools are consistent with one another, and compare favourably against results obtained using other monitoring technologies at the site.