Mineral consumption is increasing rapidly as more consumers enter the market for minerals and as the global standard of living increases. As a result, underground mining continues to progress to deeper levels in order to tackle the mineral supply crisis in the 21st century. However, deep mining occurs in a very technical and challenging environment, in which significant innovative solutions and best practice are required and additional safety standards must be implemented in order to overcome the challenges and reap huge economic gains. These challenges include the catastrophic events that are often met in deep mining engineering: rockbursts, gas outbursts, high in situ and redistributed stresses, large deformation, squeezing and creeping rocks, and high temperature. This review paper presents the current global status of deep mining and highlights some of the newest technological achievements and opportunities associated with rock mechanics and geotechnical engineering in deep mining. Of the various technical achievements, unmanned working-faces and unmanned mines based on fully automated mining and mineral extraction processes have become important fields in the 21st century

This paper reports on a comprehensive study of the CO₂-EOR (Enhanced oil recovery) process, a detailed literature review and a numerical modelling study. According to past studies, CO₂ injection can recover additional oil from reservoirs by reservoir pressure increment, oil swelling, the reduction of oil viscosity and density and the vaporization of oil hydrocarbons. Therefore, CO₂-EOR can be used to enhance the two major oil recovery mechanisms in the field: miscible and immiscible oil recovery, which can be further increased by increasing the amount of CO₂ injected, applying innovative flood design and well placement, improving the mobility ratio, extending miscibility, and controlling reservoir depth and temperature. A 3-D numerical model was developed using the CO₂-Prophet simulator to examine the effective factors in the CO₂-EOR process. According to that, in pure CO₂ injection, oil production generally exhibits increasing trends with increasing CO₂ injection rate and volume (in HCPV (Hydrocarbon pore volume)) and reservoir temperature. In the WAG (Water alternating gas) process, oil production generally increases with increasing CO₂ and water injection rates, the total amount of flood injected in HCPV and the distance between the injection wells, and reduces with WAG flood ratio and initial reservoir pressure. Compared to other factors, the water injection rate creates the minimum influence on oil production, and the CO₂ injection rate, flood volume and distance between the flood wells have almost equally important influence on oil production.

Interactions between injected CO₂, brine and rock during CO₂ sequestration in deep saline aquifers alter their natural hydro-mechanical properties, affecting the safety and efficiency of the sequestration process. This study aims to identify such interaction-induced mineralogical changes in aquifers and in particular their impact on the reservoir rock’s flow characteristics. Sandstone samples were first exposed for 1.5 years to a mixture of brine and super-critical CO₂ (scCO₂), then tested to determine their altered geochemical and mineralogical properties. Changes caused uniquely by CO₂ were identified by comparison with samples exposed over a similar period to either plain brine or brine saturated with N₂. The results show that long-term reaction with CO₂ causes a significant pH drop in the saline pore fluid, clearly due to carbonic acid (as dissolved CO₂) in the brine. Free H⁺ ions released into the pore fluid alter the mineralogical structure of the rock formation, through the dissolution of minerals such as calcite, siderite, barite and quartz. Long-term CO₂ injection also creates a significant CO₂ drying-out effect and crystals of salt (NaCl) precipitate in the system, further changing the pore structure. Such mineralogical alterations significantly affect the saline aquifer’s permeability, with important practical consequences for the sequestration process.