A 4D-3C study reveals prominent shear wave splitting anomalies in the interval directly overlying a reservoir currently undergoing a CO2 flood. The anomalies occur near the three injector wells with the highest recorded levels of bottomhole pressure. This indicates that increased reservoir pressure has affected the stress state of the overlying formations and induced observable azimuthal anisotropy. No evidence of fracturing within the confining layer exists. This new application of shear wave splitting analysis demonstrates its viability as a tool to monitor stress changes in surrounding formations and prevent undesired fracturing. It may thus provide valuable insight into enhanced oil recovery, carbon sequestration, and hydraulic fracturing operations. The use of converted wave data acquired by a dynamite source establishes that shear wave splitting analysis can be performed without incurring the costs associated with 9C surveys.


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