Restriction of gas losses in an overpressurised CO2 reservoir using gel technology

The overpressurised CO2 field Becej (Serbia) was explored in 1951. At the end of 1968, an uncontrolled gas blowout of Bc-5 well lasted 209 days resulting in 35 bars pressure drop in the reservoir until 2007. Hence, the substantial loss of reserve (> 17 billion m(3)) became a critical issue of the operator. Environmental friendly chemicals should be used only for well rehabilitation. Therefore, silicate-based method was recommended for the job. A triangle well pattern, inverted injection protocol and huge volume of treating solution were used to cure the problem. Placing the inorganic gel-forming chemicals into the target area, the annual decline of formation pressure was merely 0.03 bar/y compared to 0.9 bar/y prior to treatment. Thus, the uncontrolled gas flow was practically terminated, the loss of CO2 reserve minimised, CO2 emission to atmosphere was limited and the well against repeated gas blowout was also stabilised.