ABSTRACT
In oilfield practice, acid treatments with hydrochloric acid are the most widely used. However, hydrochloric acid contributes to the formation of organochlorine compounds both in reservoir and in oil processing. The presence of organochlorine compounds in the produced fluids leads to hydrochloric corrosion of equipment, which is very dangerous for oil refining processes. Furthermore, a large number of iron ions enter the underground reservoirs with hydrochloric acid. Iron ions form secondary sediments, which damage formation and decrease the efficiency of acid treatments. From what has been said above it is clear that, it is very important to develop hydrochloric-free acid systems for matrix acidizing. Aim of this study was development of new oil recovery stimulation technology for carbonate reservoirs using chlorine-free acid system. The components of chlorine-free acid systems were sulfamic acid, ammonium acetate, surfactant, acetic acid, corrosion inhibitor. The complex of laboratory studies included researching of interfacial tension, rate of steel corrosion, secondary sedimentation after neutralization of acid, rate of dissolution of marble, compatibility of new chlorine-free acid systems with reservoir fluids. The compatibility of new chlorine-free acid systems with reservoir fluids was investigated by using brine water and crude oils selected from carbonate reservoirs of various fields of PJSC TATNEFT. The developed acid systems reduced the interfacial tension at the boundary with crude oil to less than 0.001 N/m. Corrosion activity of the new acid systems was at a low level, which allowed injecting large volumes of acid without significant damage of oilfield equipment. Secondary sedimentation of salts after neutralization of acid was absent. The developed chlorine-free acid systems dissolved the marble much slower compared to other acids. The new acid systems are fully compatible with formation fluids. New well stimulation technology has been tested since 2017. The absolute average increase in oil production from treated wells was 0.7 tons/day (35 %). The absolute average increase of the fluid flow rate was 1.0 tons/day (41.6 %). By this method more than 3,000 tons of additional oil was produced with the continuing benefit from treatment.
