Cement Self-Healing as a Result of CO2 Leakage

Avoiding CO2 leakages from storage reservoirs is crucial to ensure safe and cost-efficient Carbon Capture and Storage (CCS). This can only be done if effort is made to maintain well integrity throughout the entire life-cycle of a well. Cement integrity is especially important, since the interfaces between cement and rock or casing have been identified as weak links in today's well construction. The present paper focuses on the healing of fractures in well cement when the material is exposed to a CO2-brine water-alternating-gas (WAG) flooding scheme. Specimen characterization using computed tomography combined with electron microscopy documents the self-healing procedure in detail for a composite cement-rock specimen subjected to a WAG flooding scheme. The study revealed volumetric data on self-healing of cement cracks and chemical changes in the specimen as well as in aqueous chemistry upon CO2 exposure. The measured aqueous chemistry suggests CO2-cement interaction to be less pronounced with time thereby together with the observed cement self-healing suggesting that the risk of compromising the safety of a storage site by cement-CO2 chemical reactions is minimal.publishedVersio

Cement Self-Healing as a Result of CO2 Leakage

Avoiding CO2 leakages from storage reservoirs is crucial to ensure safe and cost-efficient Carbon Capture and Storage (CCS). This can only be done if effort is made to maintain well integrity throughout the entire life-cycle of a well. Cement integrity is especially important, since the interfaces between cement and rock or casing have been identified as weak links in today's well construction. The present paper focuses on the healing of fractures in well cement when the material is exposed to a CO2-brine water-alternating-gas (WAG) flooding scheme. Specimen characterization using computed tomography combined with electron microscopy documents the self-healing procedure in detail for a composite cement-rock specimen subjected to a WAG flooding scheme. The study revealed volumetric data on self-healing of cement cracks and chemical changes in the specimen as well as in aqueous chemistry upon CO2 exposure. The measured aqueous chemistry suggests CO2-cement interaction to be less pronounced with time thereby together with the observed cement self-healing suggesting that the risk of compromising the safety of a storage site by cement-CO2 chemical reactions is minimal

A predictive model for the wettability of chalk

Wettability is usually measured in special core analyses of limited plug samples according to typically costly and time-consuming procedures. For comparative purposes, wettability is considered an index. The two most frequently used wettability indices are the Amott–Harvey wettability index and the U.S. Bureau of Mines (USBM) index. The Amott–Harvey wettability index is linked to imbibition characteristics and the USBM index is associated with the area under capillary pressure curves. To provide a fast analytical method, a mathematical model for predicting the wettability of chalk is presented. The model is calibrated using experimental wettability data and subsequently applied to two wells in Danish chalk oil fields in the North Sea and to outcrop chalk samples. The model supplements traditional labor-intensive laboratory measurements and predicts water wettability variations with depth by modeling both depth and porosity dependencies; in addition, it provides estimates of the effects of the aging time and displacement temperature of chalk wettability measurements in the laboratory