Experimental investigation of wellbore integrity during geological carbon sequestration: Thermal- and pressure-cycling experiments
Taofik H. Nassan, Martin Kirch, Carsten Freese, Hakan Alkan, D. Baganz, Mohammed Amro
Abstract
The long-term safety and integrity of CO2 storage in geological formations requires understanding of the interactions along the injection well between CO2 and casing, cement, and rock, which may lead to potential leakage pathways and compromise the storage security. The current knowledge on the large scale evaluation of casing-cement or cement-rock composites behavior under reservoir pressure and temperature (P&T) conditions and CO2 flow is still limited as the related experiments are challenging. Furthermore, intermittent cold CO2 injection or cooling resulting from the Joule-Thomson (J-T) effect during injection in depleted hydrocarbon reservoirs may lead to freeze-thaw cycling in the near wellbore area. Such processes have barely been investigated to date, as they are also technically demanding. In this paper, the above challenges have been addressed by constructing a test facility that includes a large scale reactor with a length of 2 m, a diameter of 0.7 m and operating pressure up to 20 MPa. The facility has been used to experimentally investigate the behavior of the casing-cement composite under P&T cycles at CO2 flow conditions. Furthermore, cement, caprock (e.g. shale), and cement-caprock composite tightness to CO2 flow was investigated on a small scale setup similar to the large scale one. The results show that cement class G, caprock (shale), cement-caprock composite remain tight. The effect of pressure cycling on casing-cement bond showed that the composite exhibits enough low permeability at ambient temperature using CO2. The effective pressure is a critical factor; the higher the effective pressure, the lower the permeability. Temperature cycling effect on the composite casing-cement was also investigated and the results showed that at subzero temperatures freezing of water in the pore space of cement caused no hydraulic conductivity (no flow of CO2), moreover, no significant change in the original permeability was observed after thawing.