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Oil and gas exploration and production activities generate large amounts of waste material, especially during well drilling and completion activities. Waste material from drilling activities to the greatest extent consists of drilled cuttings and used drilling mud with a smaller portion of other materials (wastewater, produced hydrocarbons during well testing, spent stimulation fluid, etc.). Nowadays, growing concerns for environmental protections and new strict regulations encourage companies to improve methods for the reduction of waste material, as well as improve existing and develop new waste disposal methods that are more environmentally friendly and safer from the aspect of human health. The main advantages of the waste injection method into suitable deep geological formations over other waste disposal methods (biodegradation, thermal treatment, etc.) are minimizing potentially harmful impacts on groundwater, reducing the required surface area for waste disposal, reducing the negative impact on the air and long-term risks for the entire environment. This paper gives a comprehensive overview of the underground waste injection technology, criteria for the selection of the injection zone and methods required for process monitoring, as well as a comprehensive literature overview of significant past or ongoing projects from all over the world.

We study thermal expansion, mass changes, heat capacity, and thermal diffusivity and conductivity for a ceramic body with 20 mass% and without fly ash content, using the thermodilatometric analysis, thermogravimetric analysis, differential thermal analysis, differential scanning calorimetry, and flash method. The measurements were performed: (a) for green samples either isothermally or by a linear heating up to a temperature 600 °C, 1050 °C, or 1100 °C, depending on the measurement method; (b) at the room temperature for samples preheated at 100 °C, 200 °C, ..., 1100 °C. In case (a) addition of fly ash changes the final contraction only above ~900 °C, while the thermal properties remain almost unchanged. In case (b) the final contraction of samples at 1100 °C is the same. The thermal diffusivity is nearly identical up to 700 °C, and fly ash causes the diffusivity to stay almost constant up to 1000 °C.

Wellbore instability is one of the most serious problems that can occur during drilling, mainly during drilling oil or gas wells through rocks that contain a higher proportion of clay, such as shales. To prevent wellbore instability, oil companies apply different approaches to strengthen wellbore walls, and use different shale swelling inhibitors. The aim of this research was to apply a green approach and the concept of the circular economy in mud design, and to determine whether mandarin peel powder, which is a waste material, can be used as an inhibitor of shale swelling. For that purpose, pellets consisting of bentonite and quartz in a 50:50 ratio were prepared using a compactor, and bentonite-based drilling mud (BM) with and without mandarin peel powder in concentrations of 0.5, 1, 1.5 and 2% by volume of water. The swelling of quartz–bentonite pellets after 2 and 24 h in each drilling-mud sample was determined at room temperature and 90 °C using a linear swell meter. On the basis of laboratory research, we concluded that increasing the concentration of mandarin peel powder reduces pellet swelling. By adding mandarin peel powder particles between 0.1 and 0.16 mm to the base mud at a concentration of 2% by volume of water, the following was achieved: 44% reduction in API filtration, 61.54% reduction in PPT filtration, 45% reduction in pellet swelling after 24 h at room temperature, and 48.6% reduction of pellet swelling after 24 h at 90 °C.