Fracture opening or self-sealing: Critical residence time as a unifying parameter for cement–CO2–brine interactions. (April 2016)

• Record Type: Journal Article
• Authors: Brunet, Jean-Patrick Leopold; Li, Li; Karpyn, Zuleima T.; Huerta, Nicolas J.
• Is Part Of: International journal of greenhouse gas control. Volume 47(2016:Apr.)
• Page Start: 25
• Page End: 37
• Publication Date: 2016-04
• Subjects: Well integrity -- Carbon storage -- Reactive transport modeling -- Cement fracture alteration -- CO2 leakage; Greenhouse gases -- Environmental aspects -- Periodicals; Air -- Purification -- Technological innovations -- Periodicals; Gaz à effet de serre -- Périodiques; Gaz à effet de serre -- Réduction -- Périodiques; Air -- Purification -- Technological innovations; Greenhouse gases -- Environmental aspects; Periodicals; 363.73874605
• DOI: 10.1016/j.ijggc.2016.01.024
• Languages: English
• ISSNs: 1750-5836

Abstract

Graphical abstract: Highlights: Residence time determines self-sealing or fracture opening behavior. Long residence time leads to self-sealing. The most significant alterations occur within hours to days. Abstract: Understanding long-term property evolution of cement fractures is essential for assessing well integrity during geological carbon sequestration (GCS). Cement fractures represent preferential leakage pathways in abandoned wells upon exposure to CO2 -rich fluid. Contrasting self-sealing and fracture opening behavior have been observed while a unifying framework is still missing. Here we developed a process-based reactive transport model that explicitly simulates flow and multi-component reactive transport in fractured cement by reproducing experimental observation of sharp flow rate reduction during exposure to carbonated water. The simulation shows similar reaction network as in diffusion-controlled systems without flow. That is, the CO2 -rich water accelerates the portlandite dissolution, releasing calcium that further reacted with carbonate to form calcite. The calibrated model was used for CO2 -flooding numerical experiments in 250 cement fractures with varying initial hydraulic aperture ( b ) and residence time ( τ ) defined as the ratio of fracture volume over flow rate. A long τ leads to slow replenishment of carbonated water, calcite precipitation, and self-sealing. The opposite occurs when τ is small with short fracture and fast flow rates. Simulation results indicate a critical residence time τ c – the minimum τ required for self-sealing – divides the conditions that trigger the opening and self-sealing behavior. The τ c value depends on the initial aperture size through τ c = 9.8 × 10 −4 × b 2 + 0.254 × b . Among the 250 numerical experiments, significant changes in effective permeability – self-healing or opening – typically occur within hours to a day, thus providing supporting argument for the extrapolation of short-term laboratory observation (hours to months) to long-term prediction at relevant GCS time scales (years to hundreds of years).