| Abstract |
Previous measurements have shown that gravity values in the northern and eastern parts of the main production borefield increased from the early 1970's to 1983, as a result of an influx of cool water into the steam zone. More recent measurements have shown that this increase has continued and the distribution of the changes is similar to that previously found. Gravity values, corrected for the combined effects of ground subsidence and drops in groundwater level have increased by about 400 microgal at benchmarks in the northern borefield and by 250-350 microgal in the eastern borefield, since the early 1970's. The gravity changes in the northern borefield are consistent with the value calculated from pressure changes in the reservoir. The gravity changes in the eastern borefield, however, are less than expected, possibly because saturation changes in the bottom of the steam zone there have not been as large as previously thought. Gravity changes in the western borefield have remained near zero since the early 1970's, indicating changes in saturation or thickness of the steam zone there have been small. |