Reservoir Monitoring

Advances in space geodesy (GPS and Interferometric Synthetic Aperture Radar, or InSAR) allow measurements of both horizontal and vertical deformation with low cost and high accuracy. Horizontal deformation is more sensitive to reservoir properties than is vertical deformation. This sensitivity allows stringent tests of predictions of geomechanical models and improves the accuracy of inversions for reservoir properties. GPS provides high temporal resolution with sub-millimeter accuracy at a discrete set of locations. InSAR provides high spatial resolution with typically monthly temporal resolution. The basic InSAR measurement is a line of sight change of range (look angles between 23° and 45° off nadir). The noise in these measurements is a few millimeters but they are influenced by atmospheric propagation delays that can reach several centimeters, depending on distance. ERL researchers are exploring methods for measuring along track deformation, multiple aperture interferometric (MAI) processing, and the combination of GPS and InSAR to mitigate the effects of atmospheric delay changes. Methods are also being explored which will allow single image processing of InSAR data.

Three-dimensional geodetic data is critical for discriminating between models of the processes occurring in the reservoir – pressure variations, stress changes, and fluid movements in the reservoir, which are in turn sensitive to variations in permeability. The geodetic data analyses at ERL focus on measurements of 3-D deformations through a combination and assimilation approach. Other tools include precise gravity change measurements, which yield information on deformation and density changes, and tiltmeter measurements.