GUREVICH, ALEXANDER E., and GEORGE V. CHILINGARIAN, University of Southern California, Los Angeles, CA

ABSTRACT: Leakage of Gas from Production Fields and Underground Gas Storages

Pressure decline in producing reservoirs causes subsidence with consequent deformations below and at the surface, damages to wells, and formation of fractures that increase vertical permeability. Injection of water (in the process of enhanced oil recovery) and of gas (while injecting gas into underground storage reservoirs) may form additional vertical fractures due to hydraulic fracturing. These deformations initiate or increase the gas leakage from pools, the greatest being along faults. Natural and induced (by production operations) leakage of gas reduces reserves but, at the same time, can form new, shallower gas accumulations - "secondary" reserves. Leaking gas can cause explosions and fires, and, sometimes, liquefaction of soils, especially during earthquakes. In extreme situati ns, formation of fluid diapirs is possible.

The most reasonable approach to these hazards is not to avoid them completely, but in each particular case to stermine acceptable values of subsidence and gas leakage to the surface, thus optimizing the production/hazards cost ratio. The most efficient way for this optimization, including prediction, is to combine simulation with statistical methods, using geologic characteristics selected on the basis of rigorous physical analysis. The possible existance of "secondary" reserves can be checked by additional seismic surveys. If such reserves are discovered, only reshooting of existing boreholes is necessary.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.