Characterizing Strain During Injection to Reduce Risks During CO2 Storage

Strain can potentially be used to improve characterization of reservoirs, provide warning of leaks, or improve understanding of seismicity associated with CO2 storage or related processes. We have developed a suite of instruments designed to measure multiple components of the strain tensor during injection in order to reduce risks during CO2 storage. These methods have been tested in the laboratory and under various field settings, and the resulting strain and tilt data have been evaluated with stochastic inversion and heuristic methods. One type of strainmeter uses electromagnetic sensors and it is capable of measuring the horizontal strain tensor, the vertical strain, and two tilts. We are also developing high resolution strain sensors using optical-fiber Michelson interferometers that are capable of measuring multiple strain components at high resolution without downhole electronics. A third technology uses coherent microwave photonic interferometers created with optical fibers to measure distributed strain. The sensing system we developed is capable of resolving nanostrain deformation at 1 m spatial resolution, with strain signals that range from static to 20 kHz.

New strainmeters have been deployed along with a Gladwin strainmeter at the Avant Field, a 500-m-deep oil field north of Tulsa, Oklahoma where waterflooding serves as an analog to CO2 injection. The strainmeters have been installed at a depth of 30 m near well 9A, a water injection well. Results from four, multiple-day-long injection tests demonstrate that multiple components of strain can be measured in the field and the transient signals are consistent with simulations. Analyses indicate that the ratio between fluid pressure and the reservoir elastic modulus is an important control on strain magnitude. The strain time series appears to be sensitive to the elastic modulus of the confining unit, the fluid compressibility (or gas content), the location of boundaries in the reservoir, among other effects. Trade-offs between effects of parameters are highlighted by inversion and evaluated using principle component analysis. Lab experiments using the microwave photonics system indicates it could resolve quasi-static strains of magnitudes observed during the Avant Field injection tests, and it also could detect micro-seismicity.