The process of oil and gas production, and well drilling in particular, is accompanied by waste generation [1–3]. Waste resulting from drilling operations accounts for about 90% of all oil and gas field development waste [4]. Drilling waste includes drill cuttings, used drill mud, and drilling wastewater. In the process of drilling a well, drilling fluid is supplied to lubricate and cool the tool, compensate for downhole pressure, reduce the intensity of cavern formation, strengthen the walls of the well, and bring the drilled rock to the surface. Drill cuttings are formed after the exit of used drill mud with particles of the drilled rock at the surface, and as a result of its subsequent cleaning. At the end of drilling a well or its separate interval, and upon reaching the point of no further use, the used drilling fluid also becomes waste. When the drilling site, drilling equipment, and tools are flushed, drilling wastewater is generated.
Every year, the number of wells put into operation increases, therefore, the volume of drilling waste generated also grows, which is an urgent problem that requires constant monitoring and incurs large monetary costs [5–8]. In fact, according to data from Rosneft [9], the largest oil and gas company in Russia, formed about 4 million tons of drilling cutting alone.
Drilling waste contains water, drilled rock particles, oil, and drilling mud components in various proportions. Different fields are characterized by unique composition of drilling waste and significant variation in the components to be found there. The composition of drilling waste is influenced by the drilling technologies used, the location of the oil production facility, the geological and geochemical features of the rocks, the composition of chemical reagents used for the preparation and processing of drilling fluids, etc. Drilling waste samples usually contain 0.8–7.5% oil and up to 15% organic compounds (petroleum products and chemical reagents) [10]. Drilling waste generated with oil-based drilling fluid is characterized by a higher petroleum product content in comparison to water-based drilling fluid and, accordingly, it has a more significant impact on the environment and demands a more responsible attitude [11–12].
Around the world, the treatment of drilling waste offshore and onshore differs significantly. Common methods of drilling waste treatment in offshore drilling operations are discharged into a marine environment under specific conditions [13–14] and then reinjected into a subsurface formation [15–16]. The main disadvantage of reinjection is the risk of ground water contamination.
Onshore landspreading, landspraying and land farming are widely used in the USA and Canada [17]. Periodic treatment of the mixture of soil and drilling waste (to increase aeration), and the addition of nutrients and other additives (manure, straw, etc.) can enhance the aerobic biodegradation of hydrocarbons and prevent the development of conditions that promote leaching and mobilization of organic and inorganic pollutants from drilling waste. These methods are most effective in a mild climate [18]. Drilling waste vermicomposting allows the rapid degradation of hydrocarbons and reduces the content of mineral compounds in waste [19]. The authors Kogbara et al. [20] determined that bioaugmentation, biostimulation and phytoremediation of drilling waste will reduce the content of heavy metal compounds and some volatile organic compounds. Solidification is one of the most popular methods of drilling waste disposal, allowing users to reduce the solubility and mobility of pollutants [21–24]. Thermal disposal methods are commonly used for waste generated during drilling with oil-based drill fluids [25–26]. Currently, drilling waste is also used for the production of building materials. A mixture of drilling waste and various binders (portland cement, lime, sand, loam, etc.) allows consumers to obtain materials that can be used for recultivation, and strengthening of roadside slopes, embankments, and quarries, as well as landfill dredging and reclamation [27].
In Russia, the most common method of onshore drilling waste treatment is disposal in drilling waste pits. The advantage of this method is the option for waste disposal on each multi-well pad with a capacity corresponding to the volume of drilling waste generated. However, it takes up significant land areas and poses a potential danger to the environment because of possible emissions. Drilling waste disposal in pits leads to significant environmental pollution and cannot be considered as a promising technology for drilling waste treatment. It has therefore been replaced by other technologies in numerous oil and gas companies. Currently, many technologies in the field of drilling waste management are offered in the Russian market of services and equipment. For example, several dozen technologies developed by different companies implement a common technological principle of solidification and differ in the reagents and formulations used, along with equipment and work performed.
In this regard, the need often arises to choose the most appropriate drilling waste treatment technology. Taking into account the diversity of oil and gas fields, the constantly changing legislation in the field of waste management and the development of new technologies for waste treatment, the main task is not to create a list of "ideal" technologies, but rather to develop an approach, in other words a methodology for comparative analysis of technologies encompassing all stages of the waste life cycle.
Today, there are many methods for evaluating and selecting waste management technologies in general, and drilling waste treatment technologies more specifically. In most cases, these methods are based on the use of a cost-effectiveness analysis of waste management options [28–29], a SWOT-analysis and analytical process hierarchy methods [30], and finally, a multi-criteria analysis of methods [31–32].
A common disadvantage of all these approaches to technology assessment is the lack of attention to measuring environmental impact and evaluating its long-term consequences. Therefore, applying the methodology of life cycle analysis to assess the environmental consequences of drilling waste management technologies seems to be the most optimal choice.
The methodology of life cycle analysis (LCA) is widely used today for a variety of purposes, particularly, to justify decisions in the oil and gas industry. For example, LCA is applied to estimate greenhouse gas emissions from oil production at various oil sand fields in Canada, and to compare the fuel obtained from such oil with other types of fossil fuels in terms of greenhouse gas emissions [33]. LCA is used to evaluate options for wastewater management in the production and processing of oil [34–35], and to justify the choice of drilling fluids [36–38]. LCA was also applied to compare alternative options for drilling waste management in Algeria [36, 39], and for treatment of oil-based drill cuttings [25]. Thus, life cycle assessment is a promising methodology for environmental evaluation of oil and gas deposits, and also for assessing methods and technologies of oil extraction and processing, including waste management.