Investigation Of Carbonation Degradation Of Oil Well Cement For CCUS Geological Sequestration

CO₂ capture,sequestration and utilization technology(CCUS),especially CO₂geological sequestration,is a technology that can effectively reduce CO₂emissions from large CO₂ emission point sources to the atmospheric environment and mitigate the impact of anthropogenic CO₂ on global climate change.The goal of CCUS technology is to safely and permanently store CO₂ in CO₂ reservoirs.If CO₂ were to leak out of the reservoir,the incentive to use CCUS to reduce atmospheric emissions would be greatly reduced.The results show that the cementitious surface between cement ring and rock is most prone to CO₂carbonization corrosion leading to CO₂ leakage.In order to study the Shenhua CCUS demonstration project static seal stage to the formation of security and stability of geologic sequestration,this article taking Shenhua ordos CCUS demonstration project of Majiagou reservoir rock as the research object,by simulating the real formation conditions for CO₂-salt water-oil well cement/rock reaction,in the process of the study of geologic sequestration of CO₂ injection in oil well cement/reservoir after influence of the cementation,then through using TOUGHREACT software to simulate the long geologic sequestration reaction process.This paper characterizes the static physical simulation test samples in the high-temperature and high-pressure room in terms of macroscopic changes,microstructure changes before and after the reaction,metal ion concentration changes in the reaction liquid before and after the reaction,and p H changes.The test results show that after the carbon dioxide is injected into the reactor,the carbon dioxide is quickly dissolved in the salt water(simulated formation water)solution under the actual temperature and pressure of the simulated geological storage,so that the concentration of carbonic acid in the system solution increases significantly,and carbonic acid further generates hydrogen ions And bicarbonate ions,and then a series of corrosion reactions with rock/oil well cement composite samples.In the CO₂-saline water-stratigraphic rock/oil well cement reaction,the carbon dioxide saturated saline solution will cause the dissolution of the carbonate layer in the reservoir rock part;at the same time,the carbon dioxide saturated saline solution will also undergo carbonization corrosion reaction with the oil well cement part,It reacts with calcium hydroxide and hydrated calcium silicate gel in the oil well cement to form calcium carbonate precipitates,resulting in a larger porosity in the oil well cement sample.At the same time,the TOUGHREACT numerical simulation software was used to conduct a 500-year long-period geological storage simulation test on the Majiagou Formation reservoir/oil well cement composite sample.The data obtained showed that with the extension of the reaction time,the Ca²⁺and Mg²⁺concentrations will both decrease.The increase in calcium carbonate content indicates that the calcium carbonate generated after the reaction of the carbon dioxide salt water solution with the oil well cement is accumulated and precipitated in the internal area of the oil well cement.However,since the Ca²⁺and Mg²⁺concentrations in the storage system did not change significantly over a long period of time,and the increase in calcite content also indicated that there may also be a mineralization storage process during the reaction process,it can be inferred that carbon dioxide affects oil well cement in a longer period of time.Carbonization corrosion has little effect on the storage safety of the Shenhua Ordos CCUS demonstration project.In summary,through the combination of short-period laboratory physical simulation experiments and long-period numerical experiments,this paper focuses on the carbonation corrosion mechanism of carbon dioxide saturated saline solution to the cement/reservoir cement surface of oil wells,which was demonstrated by CCUS in Shenhua The project's geological storage safety evaluation provides a certain reference basis.