Secondary recovery of gas from Gulf Coast reservoirs

Studies funded by the Gas Research Institute have provided insight into the investment decisions of a small operator engaged in SGR from an abandoned Frio sandstone reservoir in Galveston County, Texas. Favorable gas-brine ratios were obtained by rapid brine production using gas lift. The lowered reservoir pressure allowed imbibition-trapped gas bubbles to expand and merge, forming a mobile phase which greatly improved recovery. Brine was disposed by environmentally benign reinjection into a shallower, unconsolidated sand unit, although the disposal formation suffered permeability damage due to iron hydroxides in the brine. Brine solids were reduced by keeping oxygen out of the surface plumbing and performing gas-brine separation in several steps inside pressurized vessels. Periodic backflowing of the disposal well dislodged the damaged surface layer of the unconsolidated disposal sand, which was then removed from the hole by swabbing, exposing a fresh formation surface to the brine. This work has shown that the technical problems involved in secondary gas recovery can be overcome by using relatively simple solutions in line with the budget constraints of a small operator. Because secondary gas production occurs in known fields located near major gathering systems and transmission lines, it is expected to supply a significant portionmore » of future domestic natural gas.« less