The article analyzes the reuse of mineralized drilling fluids. Research methodology — analysis of scientific literature on the given problem as well as practical domestic experience.
Keywords: drilling fluids, mud, mineralized fluids, pumping, reagents, reuse
The activities of oil and gas companies are inevitably connected with the anthropogenic impact of drilling and production processes on the natural environment, so environmental protection issues are important for the industry. The peculiarity of such impact of drilling processes is high intensity and short-term formation of significant anthropogenic loads on hydro- and biosphere objects, which often exceed the threshold loads, causing disturbance of ecological balance in drilling areas.
In the process of well construction, large volumes of waste are generated, the majority of which is accumulated in sludge pits built directly on the territory of the drilling site. In the process of operation, the barns are filled with drilling and plugging muds, drilling waste water and sludge, formation water, well testing products, materials for preparation and chemical treatment of drilling and plugging muds, household waste water and solid waste, storm water.
Russia's oil and gas complex generates over 3 million tons of industrial waste annually. Of these, about 1 million tons is accounted for by extractive enterprises.
The most common way of decontamination of drilling and oil production wastes, as well as elimination of sludge pits is as follows. The barns are released from the liquid phase, which is used for various purposes (for example, they are sent to the system of oil collection and treatment with its subsequent use in the system of reservoir pressure maintenance). The rest of the sludge is covered with mineral soil. At the same time, the main objects of pollution when drilling wells are underground waters and open water bodies, soil and vegetation cover. Drilling waste is also taken to specially equipped landfills for disposal. But their maintenance demands considerable economic expenses, therefore drillers try to manage by own forces to lower the cost price of building of a well.
The greatest negative impact on the environment in the process of construction of oil and gas wells on land, which is potentially a source of groundwater pollution, has the collection, accumulation and subsequent disposal of drilling waste within the drilling site. This causes the need to search for alternative solutions to the problem, including the use of pitless method of drilling waste collection, which is considered to be the most radical solution to the environmental safety of well construction.
The problem becomes actual, if to take into account that nowadays about 70 % of volumes of drilling works fall on ecologically vulnerable areas of the far north with difficult natural-climatic and soil-landscape conditions which possess limited ability to self-cleaning and practically are not capable to protection from any kind of anthropogenic influence, and also in areas with low temperatures causing the big depth of freezing of rocks. Consequently, it is obvious that the damage caused to the natural habitat during the drilling and development of wells is obvious. Thus, the urgent tasks facing companies that have a direct impact on the construction and development cycle of wells is to minimize the generation of drilling waste.
In order to reduce the negative impact of drilling wastes on the environment, first of all, they use technologies that allow to reduce the amount of waste itself. Thus, for example, in order to reduce the volume of the accumulated solid phase in the drilling mud and, accordingly, the amount of spent drilling muds, a four-stage cleaning of the mud from the drilled rock is applied. The most affordable way to dispose of used drilling fluids is to reuse them for drilling new wells. This approach is justified not only from the ecological, but also from the economic point of view, as it provides a significant reduction in the costs of drilling mud preparation, transportation and utilization of drilling mud. However, this important and ecologically expedient direction of used drilling mud utilization is not feasible everywhere because of specific natural-climatic and landscape conditions of drilling operations areas and at considerable distance of drilling operations from each other, which is economically unprofitable. Calculations show that the cost of transportation of spent drilling muds at a distance of more than 250 km begins to exceed the cost of mud prepared on site.
Drilling wastes of oil and gas producing enterprises turn into a real source of environmental hazard. At the same time, environmental damage, for example, from the use of sludge pits, has been manifested for many years, which makes them one of the objects that cause environmental damage.
Mineralized drilling fluids can be reused in the production cycle. This applies to all types of compositions starting from weakly mineralized ones. Mineralized compositions mostly are used at those deposits, where the penetration of salts into their composition is possibly during drilling. These salts dissolve in the drilling fluids. As a result, the parameters of drilling fluids changes. They can become overly thick or overly liquid. The mineralized muds should be pumped out in the case of a loss of stability because of high reagent consumption is required to maintain their stability in the future. After pumping out the mineralized drilling fluids for reuse in production, a centrifuge can be used to separate the dispersed phases under the influence of centrifugal force. Sludge must be removed as a result and the cleaned mud reused in the production cycle.
The usage of a centrifuge allows to separate different chemical reagents according to density characteristics of each reagent. Different inhibiting agents can be added to mineralized drilling fluid in the process of preparing it. Recycling of drilling fluids reduces drilling costs. It is not always possible to recover drilling fluids. An example of this are the fields developed by Tatneft. The practice of recycling drilling fluids was successfully tested at several fields. The main task for the reusing of drilling fluids is to restore necessary properties. Recycling can use a simple scheme of separating sludge from the drilling fluids. It is passable to use a vibrating screen that separates the sludge from the drilling fluids using the vibration.
Different technologies can be used for the recycling of drilling fluids depending on the specifics of production in a particular field. It is not only about vibrating screens, but also about other technological installations, for example, centrifuges. In addition, recycling plants can be used for chemical preparation of drilling fluids for reuse in the mining industry. The main task of these technical solutions is to restore the properties of drilling fluids, which were lost after dissolution of salts in them. The specifics of recovery of drilling fluids for their reuse is that all work should be carried out directly on the well pad. As a rule, specialized enterprises are involved in this work. Additional equipment will need to be installed at the well pad if the drilling fluids are to be recycled at the well pad. In addition, it is necessary to train staff before including the recycling of drilling fluids in the extractive industry, which leads us to increase production costs.
It is inevitable that the transportation costs of mud transportation to the place of restoration of its original properties will increase if it is planned to carry out mud recycling with the involvement of a specialized enterprise. Thus, both schemes of mud recycling lead to increasing production costs. Therefore, it is necessary to prepare a feasibility study for recycling of mineralized drilling fluids. Many enterprises use the practice of utilization of drilling fluids after their preliminary neutralization due to the specifics of reuse of drilling fluids and the high costs.
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