Oil under the ground is often contained in so-called “collectors” – layers of porous rocks. In order to reach “black oil” engineers drill wells, to which oil travels from surrounding rocks through highly porous and permeable rocks and later gets extracted. During drilling of wells or after a long-term well operation pores of oil-bearing rocks get clogged and large amount of oil is left inside the Earth forever. Such clogging is also known as “wall cake” or “filter cake”.

There already exist some techniques for enhancing efficiency of oil production – treating wells with acidic solutions is one of such techniques. A solution, made with consideration for geological situation of the site, is poured into a well and under air pressure washes surrounding layers of oil-bearing rocks. Such treatment dissolves salts, which tend to block pores of these rocks, and releases oil.

Today a popular solution for treating oil-bearing wells in order to extract more oil from them is called mud acid – a mixture of hydrochloric and hydrofluoric acids with some additives. Mud acid is a liquid with low pH, which can be harmful for human health and corrode equipment. This mixture, which is quite difficult to obtain, doesn’t work good enough on all oil-bearing rocks, since it precipitates carbonates, rather than dissolves them, thus causing additional troubles with oil extraction. Using mud acid under inappropriate geological and temperature conditions can even lead to premature well deterioration.

 

 

Russian researchers, based in Russian State University of Oil and Gas, have developed an alternative mixture for treating oil-bearing wells. The innovation is a dry acid complex compound, which is less aggressive towards materials it contacts with. Such properties increase time, required for treatment, but at the same time lower risks of damaging oil wells and equipment. The compound is also less hazardous for human health. The innovative compound consists of three components: an acid, which reacts with quartziferous and argillaceous rocks; a chelating agent, which binds with calcium and iron ions, thus preventing them from precipitation; and surface-active reagent, which helps oil to get to the well and protects equipment from corrosion. A dry acid complex compound exists in the form of powder, which needs to be dissolved in a hydrochloric acid before use.

Experimental tests of a new compound have been performed in the laboratory of modeling of reservoir processes of the Institute of Oilfield Chemistry. As a model researchers have used a three-meter-thick sample of an oil-bearing rock, taken in the Irkutsk Region. During the experiment an oil-bearing well was saturated with a dry acid complex compound under temperature of 95 degrees Celsius. Twenty four hours after saturation of the rock with the solution, rock permeability was shown to increase eight per cent. New technique, developed by Russian scientists, is expected to become a great help to oil-producing enterprises and even countries.