It is well-known that one of the most widespread methods of formation shutdown during well workover and well service operations is well killing. Well killing is usually performed by means of injection of formation water and/or water solutions of mineral salts (with various densities) into formation. Field experience shows, however, that this causes the reduction of bottomhole formation zone (BFZ) permeability.

 

One of the techniques that allows to preserve porosity and permeability properties of BFZ is the mixing of well killing fluids with oil-wetting agents, which reduce surface tension on the “oil-well killing fluid” boundary. Oil-wetting agents break an emulsion in BFZ and prevent the formation of new emulsions, reduce the formation rate of salvation shells in the capillaries of hydrophilic reservoirs and decrease paraffin saturation point. It is also known that these agents significantly suppress clay swelling process, especially in clogged-up reservoirs.

 

ZAO NPF Bursintez-M has recently developed new ChAS oil-wetting agent (TS 2482-089-50199225-10), which is based on water-alcohol solution of quaternary ammonium alkyl-dimethylamine salts. ChAS oil-wetting agent can be used in oil and gas industry during BFZ acid treatments, as well as during well killing operations both in summer and winter periods. It is an effective additive for reduction of clay swelling, decreasing of well killing fluids corrosiveness and hydrophobization of rock surface. The above-mentioned oil-wetting agent has been tested by OAO VNIIneft and OAO SibNIINP at temperatures up to 900 С (1652 F). The agent is stable in sodium chloride brine (with densities up to 1,190 kg/m3 or 74.3 lb/ft3), in calcium chloride brine (with densities up to 1,300 kg/m3 or 81.2 lb/ft3) and in calcium nitrate solutions (with densities up to 1,440-1,480 kg/m3 or 89.9-92.4 lb/ft3).

 

Leak-off tests showed that utilization of oil-wetting agent increases permeability restoring coefficient up to 0.72, while in the absence of agent maximum value is 0.21. Moreover, ChAS oil-wetting agent has high microbicidal properties. At the moment full-scale test of the agent are being performed by OOO PN-Uganskneftegas.