Development and evaluation of the coaxial cable casing imager: a cost‐effective solution to real‐time downhole monitoring for CO₂ sequestration wellbore integrity

Abstract

CO2 leakage is a major concern in a geological carbon sequestration projects due to adverse environmental consequences, where the main leakage risk is identified to be along existing wells through a thick, low‐permeable cap rock. To pursue robust and cost effective real‐time downhole monitoring technology for CO2 sequestration wellbore integrity, a permanently deployed coaxial cable casing imager is developed and evaluated in laboratory in this paper. The prototype of the casing imager consists of evenly distributed coaxial cable strain sensors helically wrapped around the pipe. The system is deployed on both PVC pipe and steel pipe to test its performance in casing deformation monitoring, including axial compression, radial expansion, bending, and ovalization. The strain sensors are pre‐stressed and then helically wrapped onto the pipe with high strength epoxy. Multiple linear variable differential transformers (LVDTs) or strain gauges are used as an independent measurement of the actual pipe deformation in comparison to the casing imager measured pipe deformation. The test results demonstrated the ability of the lab‐scale casing imager prototype in real‐time casing deformation monitoring, including axial compression, radial expansion, bending, and ovalization, which would prove of great value in evaluating wellbore integrity state and providing early warnings of leakage risk that will contaminate the groundwater during CO2 injection. The low cost and high robustness of the distributed coaxial cable sensors will greatly lower the downhole monitoring cost and increase the system longevity. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

A numerical study on the feasibility of evaluating CO2 injection wellbore integrity through casing deformation monitoring

“…To improve the system's sensitivity for casing strain below 1000 με, one of the solutions is to reduce the sensor wrapping angle so that larger strain would be generated on the sensor. The current wrapping angle of the sensor is 23 degrees, and the casing strain to sensor strain correlation is represented by Eqn , where ε is the sensor strain; is the casing axial strain; ν is the Poisson's ratio of the casing material; θ is the wrapping angle of the sensor; K is the bonding factor between casing and sensor, which represents how well the casing strain is reflected on strain sensors.…”

“…To improve the system's sensitivity for casing strain below 1000 με, one of the solutions is to reduce the sensor wrapping angle so that larger strain would be generated on the sensor. The current wrapping angle of the sensor is 23 degrees, and the casing strain to sensor strain correlation is represented by Eqn (1), 15,16…”

“…10 The laboratory test on the coaxial cable casing imager shows that the system could also differentiate multiple casing deformation modes, such as axial compression, radial expansion, bending, and ovalization. 16 And the system demonstrated very high measurement accuracy in axial compression measurement in the range of 1000 με to 10 000 με with a strain resolution of 15 με, but the accuracy is much lower when the casing axial strain is below 1000 με. Both systems can be deployed permanently downhole for real-time casing deformation monitoring, thus the wellbore integrity can be evaluated throughout the whole life of the well without requiring entry into the wellbore, as opposed to the current wellbore integrity investigation technologies.…”

“…The SureView TM system claims to be able to detect and differentiate various casing deformation modes including axial compression, bending, ovalization, shearing, pressuring, and thermal expansion, with a resolution of 10 με and a strain dynamic range of ±17,500 με . The laboratory test on the coaxial cable casing imager shows that the system could also differentiate multiple casing deformation modes, such as axial compression, radial expansion, bending, and ovalization . And the system demonstrated very high measurement accuracy in axial compression measurement in the range of 1000 με to 10 000 με with a strain resolution of 15 με, but the accuracy is much lower when the casing axial strain is below 1000 με.…”

“…Real‐time casing deformation monitoring systems based on distributed strain sensors have been developed, such as the Sureview TM system, which has been tested both in laboratory and in pilot field trials, and the coaxial cable casing imager which was recently developed based on a similar working mechanism as the Sureview TM system and was evaluated in laboratory. A sketch of the coaxial cable casing imager is shown in Fig.…”