3D seismic data attribute-based characterization of volcanic reservoirs in the BZ34-9 Block, Bohai Bay Basin, eastern China

Abstract

Volcanic effusive facies (VEF) and volcanic conduit facies (VCF) are two important facies units that can be found in a volcanic reservoir or edifice. Because VEF and VCF generally exhibit opposing seismic reflection characteristics, few studies have been applied to simultaneous characterization of the two facies in seismic data. We have developed an integrated 3D seismic data attribute-based characterization technique of VEF and VCF in the BZ34-9 Block, Bohai Bay Basin, eastern China. Our method is based mainly on the 3D visualization of a thresholding display so as to separately describe the strong-amplitude reflection of the VEF with its original amplitude attribute and the weak-amplitude chaotic reflection of the VCF with its variance-cube attribute. The detailed workflow comprises four steps, including seismic facies analysis, characterization of the VEF, characterization of the VCF, and merging a display of the two volcanic-facies units. The resulting 3D image of the different volcanic facies described in the BZ34-9 Block should be able to be viewed from any perspective for a better understanding of the related genesis mechanisms of the first and second members of the Shahejie (Es12) and Dongying Formations (Ed). In total, 28 volcanic edifices have been identified on the basis of the proposed method, among which three volcanic edifices exhibited inherited eruptions, in the Es12 and the Ed. Volcanic edifices in the Es12 are distributed locally in the central part of the BZ34-9 Block, showing a central eruption style, whereas those of the Ed are characterized by a widespread distribution in the southern gentle slope of the BZ34-9 Block, revealing a composite, center-fissure eruption style. The approach should be convenient to operate and would be effective in characterizing different volcanic facies simultaneously. This application can serve as a useful reference for other basins or regions with obvious volcanic influence.