SEISMIC TIME-LAPSE MONITORING OF POTENTIAL GAS HYDRATE DISSOCIATION AROUND BOREHOLES - COULD IT BE FEASIBLE? A CONCEPTUAL 2D STUDY LINKING GEOMECHANICAL AND SEISMIC FD MODELS Pecher, Ingo A.; Freij-Ayoub, Reem; Yang, Jinhai; Anderson, Ross; Tohidi, Bahman; MacBeth, Colin; Clennell, Ben
Monitoring of the seafloor for gas hydrate dissociation around boreholes during hydrocarbon production is likely to involve seismic methods because of the strong sensitivity of P-wave velocity to gas in sediment pores. Here, based on geomechanical models, we apply commonly used rock physics modeling to predict the seismic response to gas hydrate dissociation with a focus on P-impedance and performed sensitivity tests. For a given initial gas hydrate saturation, the mode of gas hydrate distribution (cementation, frame-bearing, or pore-filling) has the strongest effect on P-impedance, followed by the mesoscopic distribution of gas bubbles (evenly distributed in pores or “patchy”), gas saturation, and pore pressure. Of these, the distribution of gas is likely to be most challenging to predict. Conceptual 2-D FD wave-propagation modeling shows that it could be possible to detect gas hydrate dissociation after a few days.
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