Carbon capture and storage (CCS) is a developed technology to minimize CO₂ emissions and reduce global climate change. Currently, shale gas formations are considered as a suitable target for CO₂ sequestration projects predominantly due to their wide availability. Compared to conventional geological formations including saline aquifers and coal seams, depleted shale formations provide larger storage potential due to the high adsorption capacity of CO₂ compared to methane in the shale formation. However, the injected CO₂ causes possible geochemical interactions with the shale formation during storage applications and CO₂ enhanced shale gas recovery (ESGR) processes. The CO₂/shale interaction is a key factor for the efficiency of CO₂ storage in shale formations, as it can significantly alter the shale properties. The formation of carbonic acid from CO₂ dissolution is the main cause for the alterations in the physical, chemical and mechanical properties of the shale, which in return affects the storage capacity, pore properties, and fluid transport. Therefore, in this paper, the effect of CO₂ exposure on shale properties is comprehensively reviewed, to gain an in-depth understanding of the impact of CO₂/shale interaction on shale properties. This paper reviews the current knowledge of the CO₂/shale interactions and describes the results achieved to date. The pore structure is one of the most affected properties by CO₂/shale interactions; several scholars indicated that the differences in mineral composition for shales would result in wide variations in pore structure system. A noticeable reduction in specific surface area of shales was observed after CO₂ treatment, which in the long-term could decrease CO₂ adsorption capacity, affecting the CO₂ storage efficiency. Other factors including shale sedimentary, pressure and temperature can also alter the pore system and decrease the shale “caprock” seal efficiency. Similarly, the alteration in shales’ surface chemistry and functional species after CO₂ treatment may increase the adsorption capacity of CO₂, impacting the overall storage potential in shales. Furthermore, the injection of CO₂ into shales may also influence the wetting behavior. Surface wettability is mainly affected by the presented minerals in shale, and less affected by brine salinity, temperature, organic content, and thermal maturity. Mainly, shales have strong water-wetting behavior in the presence of hydrocarbons, however, the alteration in shale’s wettability towards CO₂-wet will significantly minimize CO₂ storage capacities, and affect the sealing efficiency of caprock. The CO₂/shale interactions were also found to cause noticeable degradation in shales’ mechanical properties. CO₂ injection can weaken shale, decrease its brittleness and increases its plasticity and toughness. Various reductions in tri-axial compressive strength, tensile strength, and the elastic modulus of shales were observed after CO₂ injection, due to the dissolution effect and adsorption strain within the pores. Based on this review, we conclude that CO₂/shale interaction is a significant factor for the efficiency of CCS. However, due to the heterogeneity of shales, further studies are needed to include various shale formations and identify how different shales’ mineralogy could affect the CO₂ storage capacity in the long-term.

This study investigates the effects of tuning n_estimators along with max_features and min_samples_leaf in random forest regression when predicting the porosity of the Volve oil field.

Numerical investigation of optimum ions concentration in low salinity waterflooding

The modern hydraulic fracturing technique was implemented in the oil and gas industry in the 1940s. Since then, it has been used extensively as a method of stimulation in unconventional reservoirs in order to enhance hydrocarbon recovery. Advances in directional drilling technology in shale reservoirs allowed hydraulic fracturing to become an extensively common practice worldwide. Fracturing technology can be classified according to the type of the fracturing fluid with respect to the well orientation into vertical, inclined, or horizontal well fracturing. Depth, natural fractures, well completion technology, capacity, and formation sensitivity of a shale reservoir all play a role in the selection of fracturing fluid and fracturing orientation. At present, the most commonly used technologies are multi-section fracturing, hydra-jet fracturing, fracture network fracturing, re-fracturing, simultaneous fracturing, and CO2 and N2 fracturing. This chapter briefly reviews the technologies used in shale reservoir fracturing.