Procedure for Elimination of Gas-cone by Using Salt Crystals (Case Study)

Abstract

A part of the reservoirs within Hungary have got a big gas cap and a thin oil-bearing zone. During production from their vertically as well as horizontally drilled oil bearing intervals, it is typical that the rate of oil production is decreased by the gasconing. Our procedure reduces the effect of gas-coning by injecting sodium chloride saturated brine into the gas-coning oil wells. When the quantity of the solvent (water) and/or the solubility of the salt is diminished, salt crystals will precipitate in the part of pores of the reservoir. (In the German-language literature the denomination of the effect is Salzzementation) Gas-coning eliminations consist of several alternate injections of salt saturated brine, oil and ethanol slugs. After treatment, the mobile phases (gas, oil) influence salt crystals differently. It was experienced the gas is not able to dissolve the salt crystals, because it has no mobile water. Gas transports salt crystals into the pore throats, thus the "permeability barrier" in the gas flow zone remains. However, oil contains some water to dissolve the salt crystals. In the oil flow zone, the "permeability barrier" ceases gradually, and the former permeability is restored. 15 oil wells (2 horizontal ones among them) were treated for eliminating gas-coning. For surplus oil calculations, production forecasts were prepared. Surplus oil was calculated as the difference between actual and forecast production data. 67% of the treatments gave a positive result. From 1999 till the end of 2008 the project resulted in 113 000 m 3 surplus oil. Taking into account all of the treated wells, the economic result was six times larger than the input cost at least. As both horizontal wells have given good results, the procedure can be recommended for such wells especially if the reservoir is significantly heterogeneous.