Intensive comparative feasibility studies were performed in different laboratories in order to select the most promising polymer based technology for water control in gas production and storage wells exhibiting low matrix permeability, high temperature and high produced brine salinity. Core flow experiments performed under reservoir conditions with different commercial available chemical systems have pointed out to the superiority of two relatively low-molecular-weight vinyl sulfonated/ vinyl amide/ acrylamide terpolymers over other polymers to decrease selectively and effectively the water permeability without affecting the gas flow. These polymers have excellent compatibility with all types of reservoir brines and good thermal stability up to 150°C. Furthermore, because of their high shear resistance, and excellent injectability even in low permeability cores, solutions of these polymers can be pumped at high injection rates with a moderate wellhead pressure.
Based on the promising results of the lab tests the first field treatment was performed in January 1993 on an abandoned gas producing well from a sandstone reservoir with a BHT of about 130°C, an average matrix permeability of 0.01 μm2 and a produced brine salinity of more than 300 g/1 TDS. This well was loaded up with water. The polymer solutions were injected at a well head pressure not exceeding 5 MPa without any problem. The treatment returned a daily gas production of more than 100,000 m3 to the well. The water production was reduced from almost 90 m3/d to less than 1 m3/d. The second treatment was performed in May 1994 on a candidate well in a gas storage sandstone reservoir with a BHT of 87°C, matrix permeability of 0.1μm2 and brine salinity of 300 g/l. According to the lab feasibility studies this time a terpolymer with a lower molecular weight was used. As a consequence of the treatment the well is showing far better gas injection characteristics. The effect on the gas and water production can only be evaluated at the end of the winter production period in March 1995.