Abstract
Abstract Seismic dispersion and fluid mobility attributes are used to characterize a volcanic gas reservoir in the Songliao Basin of China. A rock physics model is constructed to describe poroelastic behaviors associated with heterogeneous fluids saturation within the volcanic gas reservoirs, where velocity dispersion and attenuation of propagating waves are attributed to the wave-induced fluid flow described by the patchy saturation theory. Modeling results indicate that the frequency-dependent bulk modulus at the seismic frequency is more sensitive to gas saturation than the P-wave velocity dispersion. Accordingly, a new inversion method is developed to compute bulk-modulus-related dispersion attribute DK for improved characterization of volcanic gas reservoirs. Synthetic tests indicate that DK is more sensitive than traditional P-wave dispersion attribute DP to the variations of reservoir properties. The high value of dispersion attribute DK indicates the volcanic gas reservoirs with high porosity and gas saturation. At the same time, fluid mobility attribute FM can discriminate the volcanic gas reservoir as DK. Field data applications illustrate that DK and FM exhibit anomalies to the gas zones in the volcanic gas reservoir on the cross-well section. However, DK is more robust than FM to identify favorable zones on horizontal slices for specific target layers. Overall, rock physical modeling provides insights into the poroelastic behaviors of volcanic gas reservoirs, and inversion for seismic dispersion attribute DK improves hydrocarbon detection in the volcanic gas reservoir.
Highlights
As a type of essential unconventional reservoir, the volcanic reservoir plays a significant role in hydrocarbon production
Estimating seismic dispersion attributes and fluid mobility is essential for better characterizing volcanic gas reservoirs
We built a rock physics model for the volcanic gas reservoir to describe poroelastic behaviors associated with heterogeneous fluid saturation in volcanic rocks
Summary
As a type of essential unconventional reservoir, the volcanic reservoir plays a significant role in hydrocarbon production. The volcanic gas reservoir of the Songliao Basin in northeast China contributed an increasing amount of gas production in recent years This volcanic gas reservoir is located in the formations related to multiple-period volcanic eruptions, representing a heterogeneous stratigraphic structure with very low porosity and permeability. Complex microstructure makes it challenging to get insights into rock physical properties and associated seismic responses of the volcanic gas reservoir. It is demanding to develop practical seismic techniques to discriminate favorable volcanic gas reservoirs based on rock physical modeling Seismic techniques such as amplitude variations versus offset (AVO) are usually used to identify lithology and fluids in a hydrocarbon reservoir. Russell et al [5] proposed a generalized AVO representation to calculate fluid properties by incorporating the poroelastic theory
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