Analysis of cementing carbonation during Co2 sequestration

Abstract

Effects of global warming are well-known to be caused by emissions of greenhouse gases. As an effort to alleviate the gases production, Capture and Sequestration (CCS) is implied in oil and gas practices where carbon dioxide gas (CO2) is captured from different emission sites and injected into geological formations. However, problems arised in sequestration projects as exposure of CO2 degraded the Portland-based cement in the wellbore. Consecutively, the cement cracked and leakage of CO2 contaminated the underground drinking water. Hence, this paper aims to understand the physical and chemical reaction between CO2 and Class G cement further. Class G cement was obtained from Schlumberger Kemaman Supply Base and tested with water according to American Petroleum Institute (API) standard which water to cement ratio was set to 0:44:1. All of the samples were exposed to CO2 for six, eight and ten days accordingly and analyzed with unconfined compression, Field Emission-Scanning Electron Microscope (FESEM) and X-Ray Diffraction (XRD) testings. Ten days of CO2 exposure towards Class G cement showed the lowest compressive strength as to be compared to other samples. Carbonation reaction between water and CO2 was diagnosed to take place causing the cement to loose its strength. FESEM analysis on the other hand showed that the surface of the sample were uneven with long-shaped crystals with supporting XRD data presented large number of calcium carbonate ((Ca(CO)3). Nevertheless, the unexposed sample showed the opposite result with highest value of compressive strain and large number of calcium hydroxide ((Ca(OH)2).