Prevention of Vertical Gas Flow in a Collapsed Well Using Silicate/Polymer/Urea Method

Abstract

Abstract The overpressurized CO2 field Becej (Serbia) was found in 1951. At the end of 1968, drilling a well, an uncontrolled gas blowout happened and lasted for 209 days. The disaster claimed human lives and huge gas loss until it was spontaneously killed by collapse of the well5. Hence, the substantial loss of reserve (>17 billion m3) became critical and urgent actions had to be taken to stop the vertical gas migration. As a precondition, environmentally friendly chemicals could be used for restriction of vertical gas flow in the collapsed well. Therefore, silicate solution aided by polymer and urea was recommended for the job utilizing its auto-gelation in CO2 rich media. The triangle well pattern was the basis of operation consisting of an observation and a newly drilled directional well that served for injection of the treating solutions. The inverted injection protocol and huge volume of treating solution jointly proved satisfactory to provide extensive pillow around the well filling up also the accumulated debris at the bottom and open vertical hole. Restriction of vertical CO2 migration in and around the collapsed well was successfully completed in the middle of 2007. As a result of treatment, the annual decline of formation pressure was merely 0.03 bar/y compared to 0.9 bar/y before the treatment. Further, other indications in the damaged and the observation wells have shown that the uncontrolled gas flow was considerably restricted or completely stopped. The successful restriction of gas migration into the upper layers (and the atmosphere) preserves the CO2 reserve, limits CO2 and GHGs emission to atmosphere and stabilizes the collapsed well against potential danger of repeated gas blowout.