Effects of CO2-induced Reaction on the Transport Properties of Debonded Well Cement-Casing Interfaces: Reactive Flow-through Experiments on the Metre Scale

Tuesday, 16 December 2014: 3:10 PM
Timotheus K T Wolterbeek1, Colin J Peach2 and Christopher James Spiers2, (1)Utrecht University, Utrecht, 3584, Netherlands, (2)Utrecht University, Utrecht, Netherlands
Debonding between casing and cement may create interfacial leakage pathways, compromising well integrity in CO2 storage systems. Our previous work on such debonding-defects showed that chemical reactions between cement, steel and CO2-fluids provide only limited potential for local reaction-induced sealing, allowing short-range defects to remain open. Changes in temperature and stress state may subsequently cause these defects to grow and connect, potentially forming long-range interfacial leakage pathways. This study investigates how CO2-induced reaction affects the transport properties of such interconnected defects by means of reactive flow-through experiments.

Metre scale sections of debonded cement-casing interface were simulated using composite samples, prepared as follows. Cement was cast into steel tube coils (L 1.5–3.0 m, ø 6–8 mm). After curing, the coils were pressurized using water, causing the steel tube to deform permanently and lift off the cement, creating casing-cement samples that contain sections of (partially) debonded cement-steel interface.

Reactive flow-through experiments were performed in a permeameter, capable of running at temperatures (80°C ± 0.5 °C) and fluid pressures (10–12 MPa) representative for downhole environments. The coil samples were one-sidedly flooded with CO2-bearing fluid, continuously measuring apparent sample permeability and periodically sampling the downstream fluid. Additionally, post-experiment microstructural analyses were performed. Results show permeability decreases of several orders, indicating reactive-transport phenomena that occur on the metre scale contribute significantly to the sealing-potential. As such, our experiments can be used to understand the long-range behaviour of annuli in wells, beyond the commonly used lab-scale.