Poster

[MO-P-01] Practical hybrid gravity monitoring

*Mituhiko Sugihara¹, Hiroki Goto¹ (1. Geological Survey of Japan, AIST (Japan))

Recently, absolute/relative hybrid gravity measurements have been made in many fields for practical purposes such as geothermal exploitation, oil/gas fields, water resources, and CCS. However, the benefits of hybrid monitoring have not been sufficiently applied. Generally, this technique is effective to delineate the spatial distribution of gravity changes within a few microgals. However, such precise observations are not always feasible due to the error of absolute gravity measurements as well as the unstable behavior of the relative gravimeters. The hybrid method is apt to be ineffective when an absolute gravimeter is installed at a remote location. Now we reviewed the hybrid gravity data from a geothermal field and succeeded in delineating a reliable spatial distribution of gravity changes. Short-term and long-term trends were evaluated with an absolute gravimeter installed at the center of the production area. It provides a reliable datum for the continuous processing of piecewise relative gravity data. The short-term drift of the relative gravimeter, which was observed to be larger than that of another relative gravimeter, was better corrected by an exponential drift function than a power series drift function. Particular characteristics of the observations were derived by the method independent of reservoir modelling. It is effective to evaluate reservoir response in the time domain as well as in the spatial domain.