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Cross-borehole electrical resistivity tomography (CHERT) technology has been implemented in field-scale CCS/CCUS (carbon capture and storage/carbon capture, utilization and storage) projects. It is highly desirable to investigate how to optimize the design of the ERT electrode arrays and corresponding working schemes for both laboratory experiments and field applications. A CHERT system was developed for laboratory experiments of CO2 geological storage applications. An optimization method was established for optimizing the structure of electrode arrays and corresponding working schemes. The developed CHERT system was calibrated systematically to determine the measurement range and accuracy of electrical impedance. Laboratory experiments were designed and implemented to validate the performance of the developed CHERT system. It has been illustrated that: (1) It is an essential step to optimize the structure of electrode arrays and corresponding working schemes of CHERT according to the real application background. The optimization method based on finite-element modelling provides an effective means for designing a field-scale CHERT system. (2) The quality of the images inverted from the CHERT data is highly dependent on the working schemes and specific modes, which is closely related to the size of the data sets used for the inversion. The AM-BN scheme is recommended due to the better uniformity of the resultant sensitivity field and application to larger borehole spacing. (3) Based on the calibration, the measurement range of the developed CHERT system can be determined as 100 Ω to 4.5 kΩ with an error limit of 1.5%. The maximum relative errors of the impedance magnitude and phase angle are 5.0% and 7.0%, respectively. Based on the test results the location of the CO2-bearing objects can be identified accurately. The shapes of the tested objects present distortion to some extent, but this can be alleviated by selecting working modes with a larger size of data set. [ABSTRACT FROM AUTHOR]

CO2 sequestration in saline aquifers is one of the most potential sequestration modes, and saline aquifers are ideal sites for CO2 geological sequestration. After CO2 is injected into a saline aquifer, it will have a long-term complex geochemical reaction with the formation of minerals and water, and the minerals will undergo multiple reactions such as dissolution and reprecipitation. Therefore, an in-depth study of the geochemical reaction mechanisms between CO2 and formation minerals is of great significance to the accurate calculation and prediction of CO2 storage volume and the safety evaluation of long-term CO2 sequestration. In China, continental saline aquifers are widely distributed, whose mineral compositions and texture maturity are markedly different from those of the marine sedimentary basins in North America, and their stratigraphic environments are more complicated. The studies on the CO2–water–rock (mineral) still have many research gaps or insufficiencies, and there is no report on the dissolution mechanisms of individual minerals in the reaction. Taking one certain block of Daqing Oilfield, which is a typical continental deposit in China, as an example, we analyze the dissolution laws and four types of typical continental deposited minerals under the effect of CO2 and the change features of ionic compositions and pH of the formation water in the process of geochemical reaction. The research results indicate that CO2 has different dissolution degrees for the four types of minerals, among which, feldspar, as the main mineral in continental sedimentary formations, has the lowest dissolution rate. Furthermore, in terms of the water type (Na+-enriched NaHCO3) of the saline aquifer in the deep part of the continental deposit, feldspar can precipitate into the secondary minerals represented by dawsonite in the later stage, which can act as the potential minerals of carbon fixation to increase the CO2 mineralization storage volume in continental deposited saline aquifers. [ABSTRACT FROM AUTHOR]