Nano-Computed Tomography Analysis of Downscaled Cement Sheath Samples: Insights into Porosity Distribution

Mitigating greenhouse gas emissions from hydrocarbon wells is an industrywide challenge, with microstructural variations in the cement sheaths lining the wells recognized as key factors in forming leakage pathways. To better understand the microstructural variations in cement sheaths and the corresponding mechanisms, downscaled samples simulating rock–cement–casing and casing–cement–casing cement sheaths were prepared and then scanned using nano-computed tomography at resolutions of 11.93 μm and 6.80 μm, respectively. Both the radial and axial porosity of regions of interest were quantified and analyzed. The results showed that radial porosity distributions were quite different between the rock–cement–casing and casing–cement–casing samples. In the rock–cement–casing samples, the radial porosity decreased from the cement–rock to the cement–casing interface due to cement migration, while in the casing–cement–casing samples, the highest radial porosities occurred in both the cement–casing interfaces due to the influence of an interfacial transition zone. The axial porosity distribution was similar in all the rock–cement–casing and casing–cement–casing samples because the porosity decreased from the top to the bottom due to the particle settling phenomenon. These findings enhance our understanding of the factors affecting gas leakage pathways from wells, and the proposed methodology can be used to optimize cement blends to produce effective wellbore barriers.