P- 144 New Developments in Gravity Applications and Instruments

Gravity meters are commonly used to map spatial changes in the earth’s gravity, achieving resolution of parts per billion on microgravity surveys. The application of gravity surveys to monitor change and recent improvements in gravity instrumentation will be summarized. The use of gravity to track the progress of a waterflood in Prudhoe Bay, Alaska, provides a 4D Gravity case history. The surface gravity change caused by the injection of water into the gas cap is measured annually and compared to the expected change calculated from the reservoir model. Monitoring injected products using non-intrusive, inexpensive surface gravity measurements provides an effective “early warning system ” for injection and sequestration projects. A recent borehole gravity survey in Hanford, Washington, demonstrates the ability to measure bulk densities using a borehole gravimeter. The applications include geotechnical studies at waste disposal sites, bridges and structures, locating and monitoring thief zones in reservoirs, and grade control in iron mines. Recent and ongoing improvements in borehole gravity instrumentation will result in the introduction of a new borehole gravity meter during 2008 that can be used in smaller, inclined boreholes. Earth tides are commonly measured with gravity meters. Other long period movements of the earth can also be recorded by suitably configured gravity meters. The ground shaking in Luxembourg before and after the January 13, 2007, earthquake in Japan was recorded on a long period seismometer, a superconducting gravity meter and a new portable gPhone gravity meter. The match between the seismometer data and the gPhone data during the earthquake is excellent. The gPhone continued to record the arrival