--> --> Abstract: Geochemical Monitoring During the CO2 Injection Test at Lost Hill, California, by David R. Cole, Michael F. Morea, and B. Mack Kennedy; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Geochemical Monitoring During the CO2 Injection Test at Lost Hill, California

David R. Cole1; Michael F. Morea2; B. Mack Kennedy3

(1) Earth Sciences, The Ohio State University, Columbus, OH.

(2) Chevron USA, Bakersfield, CA.

(3) Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA.

Identifying and quantifying the processes affecting CO2 transport for a given subsurface environment is essential to predicting the residence time of CO2 and estimating the storage characteristics and capacity of that reservoir. Tracer studies have become an important technique for in-situ subsurface characterization, allowing detailed interrogation of complex systems which have components moving, mixing, and reacting. Naturally-occurring elements, such as the stable isotopes of the light elements (O, H, C, S, N), and noble gases and their isotopes (He, Ne, Ar, Kr, Xe) can be used to determine the sources of fluid and gas species and their mechanisms of migration, assess the extent of fluid/rock interactions, and quantify the residence times of fluids in the subsurface. The objective of this study was to document the gas chemistry and isotopic compositions of gases and fluids sampled during a combined CO2 and H2O injection test conducted at ChevronTexaco’s Lost Hills, CA oil field. The primary focus of this reconnaissance study was on the major carbon-bearing gases (e.g. CO2, CH4, etc.), their stable isotopes (e.g. 13C/12C, 18O/16O), and the chemistry and isotopes of the noble gases (e.g. Ar, Kr, Xe, etc.). The question we addressed was whether or not the stable isotope signals of CO2 and other reservoir constituents (such as the noble gases) could be used to assess the behavior of CO2 in the subsurface. Our results indicate the following:

(1) 13C isotopes indicate that indigenous reservoir CO2 is significantly different from the CO2 injectate by as much as 50 per mil;

(2) The contribution of CO2 injectate to the system can be quantified by mass balance modeling of gas and isotope (stable; noble) chemistry;

(3) This approach clearly demonstrates that increases in CO2 and more depleted 13C values correlate with periods of CO2 injection;

(4) During water flood events, the CO2 gas contents decrease and the 13C values in CO2 return to more “reservoir-like” in magnitude;

(5) Certain observation wells communicate with the injection wells far more readily than others, which may be controlled, in part, by faults that strike NE-SW;

(6) Disagreement between the % contribution of injectate estimated from gas chemistry vs. isotopes can be used to assess interaction among gas-rock-fluid.