Seismic response characteristics and distribution prediction of Permian volcanic rocks in the Guanghan area, western Sichuan

The Permian strata in the Guanghan area of western Sichuan feature thick volcanic rock layers.Due to the lack of drilling, large burial depth, low quality seismic data, complex lithofacies changes, and complicated stratigraphic contact relations, the existing seismic data cannot accurately identify the internal stratigraphic structure of the volcanic rocks, volcanic channels, and the boundary between the volcanic rocks and surrounding rocks, affecting the oil and gas exploration in these volcanic rocks.Based on the actual drilling data from the study area, two forward models of central and fractured volcanic institutions were established to simulate the changes in seismic reflection characteristics caused by changes in lithology, lithofacies, and thickness of different volcanic rocks.The forward simulation results indicate that①The thickness of the volcanic body is thickened and the outside is in a mound shape.②The boundary of the volcanic facies between different eruptions was characterized by an oblique reflection with a variable continuity.③Differences in lithology, lithofacies, thickness, and wave impedance all affected the imaging results.If the thickness was greater than 60m, the internal structure of the volcanic rocks could be clearly imaged (in particular, basalt was the easiest to identify).④The imaging of the volcanic channel showed interruptions, blanks, and weak features, but wider portions were easier to identify.⑤Volcanic bodies affected the imaging of the underlying strata, resulting in phase pull-up, energy shielding, and false structures.Nonetheless, the modeling results led to a clear identification of the complex structural characteristics of the Permian volcanic rocks in Guanghan area, western Sichuan.On the basis of the seismic facies and various seismic attributes representing the characteristics of volcanic rocks, it is predicted that thick and large explosive facies and effusive facies volcanic rocks are mainly distributed in well A and in the central part of the study area.The results of this research could be used to guide the prediction of volcanic reservoirs and the deployment of well locations in the next step of development.