--> ABSTRACT: Secondary Recovery of Gas from Gulf Coast Reservoirs, by Daniel J. Soeder and Philip L. Randolph; #91022 (1989)

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Secondary Recovery of Gas from Gulf Coast Reservoirs

Daniel J. Soeder, Philip L. Randolph

Water-drive gas reservoirs on the U.S. Gulf Coast are typically abandoned when large volumes of formation brine begin to be produced. Many of these abandoned fields still contain up to half of the original gas in place, making them a significant domestic gas resource. Where the initial field development costs were recovered by the original operator, the economics for production of this abandoned gas can be very positive. Two factors are important to the costs of secondary gas recovery (SGR): favorable gas-brine ratio in the produced fluids and inexpensive, environmentally safe disposal of the waste brine.

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 b ckflowing 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 portion of future domestic natural gas.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.