Improvements in the sensitivity of gradiometers have opened up the possibility of new applications of gravity gradiometry. For example, it may now be possible to detect the subtle signal variations of time-lapse reservoirs. In this paper, we evaluate the feasibility of using gravity gradiometry as a monitoring tool for SAGD (steam-assisted gravity drainage) reservoirs. SAGD is an ideally suited time-lapse gradiometry problem due to the shallowness of the formations and large density contrasts caused by steam replacing heavy oil. We begin by developing a test model that is a first-order approximation to the density change produced by the growing steam chamber within the subsurface. Using this model, we first analyze the predicted signal and compare it to current and predicted next-generation instrument sensitivities. We then expand to a more realistic multi-well SAGD problem, with varying density contrast and deviating plumes, to develop a workflow that includes inversion to understand the ability of this method to recover information about steam chamber integrity.
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