Southwest Petroleum University, China
Prof. Xiaoyang Guo is an academic leader of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, vice-director of Cementing group of Chinese Petroleum Society (CPS), senior expert of Drilling Engineering Standardization Technical Committees of China National Petroleum Corporation (CNPC), member of Society of Petroleum Engineers (SPE). Prof. Guo’s researches focus on the operation safety and integrity of deep and ultra-deep well. Studies on the basic theory and applied technology of cementing engineering and cement slurry systems. He has obtained 12 patents and published 70 articles and 3 industry standard of CNPC.
H2S is an acidic and toxic gas and the corrosion of H2S on oilwell cement is considered to be a great challenge for wellbore integrity and environmental safety in the exploitation of high-sulfur gas reservoir. In our work, an unidirectional sample was designed to simulate the actual downhole condition, and the corrosion performances of oilwell cement exposed to humid H2S gas and H2S rich brine were investigated using designed unidirectional samples. Compressive strength, microhardness, porosity, gas permeability, SEM, EDS, and XRD analyses were conducted to compare the dissimilarity of H2S attack in two exposure scenarios. The experimental results show that the corrosion degree of cement exposed to humid H2S gas was lower due to a dense gypsum layer formed on the cement surface; this layer inhibited inward penetration of H2S by blocking diffusion. On the contrary, a porous and loose amorphous silica gel section formed on the headspace of brine-exposed cement for dissolution and migration effects of brine, which facilitated the penetration of H2S to the interior of cement. The degradation mechanism of cement and the effects of exposure scenario on cement properties are proposed.