Export 4 results:
Sort by: Author [ Title  (Asc)] Type Year
A B C D E F [G] H I J K L M N O P Q R S T U V W X Y Z   [Show ALL]
Eiken, O, Stenvold T, Zumberge M, Alnes H, Sasagawa G.  2008.  Gravimetric monitoring of gas production from the Troll field. Geophysics. 73:WA149-WA154.   10.1190/1.2978166   AbstractWebsite

Four surveys of relative gravity and depth measurements have been conducted over the Troll field since gas production began in 1996. Precision in gravity (intrasurvey repeatability measured as standard deviation) has improved from 26 mu Gal to 4-5 mu Gal in two surveys in 2002 and 2005. The scatter of 74 station depth differences (standard deviation) has improved to 1.0 cm (with modeled subsidence removed) for the same two surveys. Subsidence of up to 3 cm is observed above the thickest reservoir of Troll East between 2002 and 2005. Time-lapse gravity shows a general slight average increase in Troll East (95% confidence for the interval centered at 5.2 +/- 4.4 mu Gal), which is likely caused by edgewater influx. One gravity station close to Troll A shows a 9-mu Gal gravity increase, indicating 2.2-m water rise. Repeated logging in a nearby well indicates 2.8-m rise. These two observations agree within uncertainty bounds. Gravity decrease in Troll West is explained by oil production and a downward-moving gas-oil contact. Gravity increases in two areas in the easternmost part appear statistically significant and are likely to have been caused by edgewater influx. This has not been confirmed by other data, but aquifers located near these areas make the results plausible. The gravity and subsidence data give estimates of total mass influx and pore compaction; these data have been used in and agree with material-balance calculations.

Zumberge, M.  2011.  Gravity Measurements, Absolute. Encyclopedia of Solid Earth Geophysics. ( Gupta HK, Ed.).:494-497., Dordrecht: Springer Abstract
Zumberge, M.  1995.  Gravity Meter. McGraw Hill Encyclopedia of Science & Technology. Abstract
Zumberge, MA, Ander ME, Lautzenhiser TV, Parker RL, Aiken CLV, Gorman MR, Nieto MM, Cooper APR, Ferguson JF, Fisher E, Greer J, Hammer P, Hansen BL, McMechan GA, Sasagawa GS, Sidles C, Stevenson JM, Wirtz J.  1990.  The Greenland Gravitational Constant Experiment. Journal of Geophysical Research-Solid Earth and Planets. 95:15483-15501.   10.1029/JB095iB10p15483   AbstractWebsite

An Airy-type geophysical experiment was conducted in a 2-km-deep hole in the Greenland ice cap at depths between 213 m and 1673 m to test for possible violations of Newton's inverse square law. The experiment was done at Dye 3, the location of a Distant Early Warning Line radar dome and the site of the deepest of the Greenland Ice-Sheet Program (GISP) drill holes. Gravity measurements were made at eight depths in 183-m intervals with a LaCoste&Romberg borehole gravity meter. Prior to the experiment the borehole gravity meter was calibrated with an absolute gravity meter, and the wireline depth-rinding system used in the borehole logging was calibrated in a vertical mine-shaft against a laser geodimeter. The density of the ice in the region was calculated from measurements taken from ice cores obtained from earlier drilling observations. Ice penetrating radar was employed in order to correct the gravity data for the topography of the ice-rock interface. Surface gravity observations were made to assess the extent to which density variations in the sub-ice rock could affect the vertical gravity gradient. The locations of the gravity observation points were determined with a combination of GPS recording, first-order leveling, and EDM surveying. An anomalous variation in gravity totaling 3.87 mGal (3.87×10−5 m/s2) in a depth interval of 1460 m was observed. This may be attributed either to a breakdown of Newtonian gravity or to unexpected density variations in the rock below the ice.