GEODYNAMIC EFFECTS INDUCED BY DISTANT EARTHQUAKES IN NATURAL GAS FIELDS

Abstract

A discussion is presented of geodynamic effects produced by distant earthquakes, as exemplified by the active Karachaganak gas-condensate field, located in a seismically inactive zone in northwestern Kazakhstan. The upper, rift-generated part of the field, at depths from 3700 to 4500 m, is now being worked. The initial formation pressure and temperature were 550 kg/cm2 and 74°C. The productive sequence consists of low-permeability carbonate reservoir rock. The formation fluid has a high content of heavy hydrocarbons (C5H12 and higher), i.e., 450 g/m3. The gas-condensate system is undersaturated in gas, and the pressure of the onset of condensation is 420 kg/cm2. Based on data analysis, it is found that the effect produced by a strong earthquake is manifested as a significant decrease in the gas and condensate yield, with subsequent relaxation, which also depends on the number and magnitude of aftershocks.