Stress-transfer characterization in a concrete-rock system using DSS measurements

Well-based Fiber Optic Cable (FOC) constitutes a novel technology for sensing and monitoring, with high spatial resolution, strain resulting from changes in reservoir pressure due to thermal, mechanical, and hydraulic stresses triggered by critical activities which endanger wellbore stability.

As wellbore integrity assessments depend on reliable, calibrated strain measurements, the strain recorded in such configurations needs to be corrected for coupled stresses across multiple media, such as cement-formation systems.

In this research, we aim to enhance the understanding of mechanical stress transfer in cement-rock formation systems through laboratory experiments by recording and comparing FOC strain measurements with 2-D strain-gage measurements.

We crafted two cylindrical sandstone samples of 50 mm diameter and 100 mm height with a concentric hole where concrete of standard mix was poured; one of the samples is equipped with a segment of fiber-optic cable coiled at the concrete-rock interface, and a second segment coiled around the external surface of the rock sample. The second sample is equipped with a set of 2D strain gauges: three are placed at the concrete-rock interface, and three more on the external surface of the sandstone.

Both samples are subjected to the same stress protocol: cyclic uniaxial compression with increments at the end of each cycle over the entire elastic regime until yielding.

The end goal is to provide FOC data calibration for formation-cement interface under uniaxial mechanical stress, as well as providing insights into the micromechanical behavior of the formation-cement interaction.

This work was supported by CETP Q-Fibre (proposal code Cetp-FP-2023-00079). CETP Q-Fibre is co-funded by the European Commission (GA no. 101069750), the Netherlands Enterprise Agency (RVO), the Research Council of Norway (RCN), and the U.S. Department of Energy (DOE).