<
p>
Injecting fluid into a well creates an evolving strain tensor field in the rocks enveloping the well. Understanding the strain field has the potential to improve the effectiveness of CO<
sub>
2<
/sub>
storage, but the strain tensor had never been measured during injection. The objective of this project was to evaluate how the strain tensor can be measured and interpreted to improve the assessment of geomechanical properties and advance an understanding of geomechanical processes that may present risks to CO<
sub>
2<
/sub>
storage. The project consisted of three primary tasks related to 1) developing instruments for measuring the strain tensor with high precision
2) developing methods for analyzing strain signals
and 3) demonstrating the approach at a CO<
sub>
2<
/sub>
storage analog site. <
/p>
<
p>
The primary contribution of this project is that it showed that that the in-situ strain tensor can be measured during injection into a reservoir, and the data can be interpreted to yield insights into reservoir properties and geometry that would be valuable to CO<
sub>
2<
/sub>
storage projects. <
/p>
<
p>
Specific contributions include: <
/p>
<
ol>
<
li>
The project demonstrated the ability to characterize a strain signal at rates of tens of nanostrain per day that was repeatable over multiple injection tests. <
/li>
<
li>
Demonstrated feasibility of measuring the strain tensor at shallow depths (30 m) while injecting into a reservoir at 530 m. These data show that horizontal strains are tensile, with the circumferential strain larger than the radial strain. Vertical strain is compressive and similar in magnitude to the average horizontal strain. The data are similar to results from simulations. This appears to be the first time the transient strain tensor caused by injection has been measured. <
/li>
<
li>
Developed two new strainmeter instruments capable of measuring strains during injection. One instrument measures the vertical strain, the horizontal strain tensor and two tilts using electromagnetic sensors. The other instrument measures areal strain using simple, inexpensive optical fiber sensors. <
/li>
<
li>
Showed that areal strain data from the optical strainmeter are virtually identical to baseline data from a state-of-the-art Gladwin strainmeter. Low cost, high resolution and verified performance make the optical strainmeter design ideal for use during future CO<
sub>
2<
/sub>
storage projects, or similar applications. <
/li>
<
li>
Developed four quantitative methods for interpreting strain signals. Derived a new analytical solution for deformation during injection. Developed a stochastic inversion technique well suited to 3D poroelastic problems. Devised a simple graphical method for preliminary interpretation of strain signals. <
/li>
<
li>
Used four independent interpretation methods to predict material parameters (e.g. permeability, elastic modulus, hydraulic diffusivity, Biot-Willis parameter) and reservoir geometry that are consistent with each other and with independent estimates from the field site. This information would be useful for planning a CO<
sub>
2<
/sub>
storage project. This appears to be the first time these reservoir parameters were estimated in-situ using a signal measured at a single location at shallow (30 m) depth. <
/li>
<
li>
Established publication of strain data from a well field in near real time to a publically accessible, archived database maintained by IRIS. Data available at: http://ds.iris.edu/mda/2J/.<
/li>
<
/ol>