Multicomponent PP and PS Seismic Response from Volcanic Gas Reservoirs

Here we present an example of using PP and PS converted-waves for characterizing volcanic gas reservoirs in Daqing Oilfield in Northeast China. The volcanic targets are buried at depth raging from 2800m to 3600m, which often give rise to incoherent P-wave response. To overcome this problem, a multicomponent seismic experiment was set up to evaluate the converted-waves recorded by digital MEMS (micro-electro-mechanical system) sensors. The experiment includes six 2D lines, passing through ten boreholes drilled for the volcanic reservoirs. Several multicomponent VSPs have also been acquired for correlation purposes. Analysis the P- and S-waves from the target formation at the ten borehole locations reveals very consistent P- and S-wave amplitude anomalies. From the gas producing wells, the P-wave reflection is consistently weak and scattered, whilst the PS-wave reflection are consistently strong and continuous. In contrast from the non-producing wells, both PP- and PS-waves show continuous and strong reflections. The gas reservoirs can then be delineated from joint PP- and PS-amplitude analysis and the results agree with the drilling results in the study area. This provides conclusive evidence demonstrating the benefit of multicomponent seismic data from digital MEMS sensors.