Abstract
High-amplitude events in seismic reflection profiles of oil and gas reservoirs are the exploration “bright spot” target, as have also been observed in recent borehole acoustic reflection imaging applications. This paper uses the cracked porous-medium elastic wave theory to analyze the cause of this phenomenon. We model the reservoir as layered cracked porous media and analyze the effect of wave-induced squirt flow in a multi-crack system on acoustic reflection. The propagator matrix method can generally be used to calculate wave reflection and transmission through the layered reservoir model. In particular, for a single fracture layer, assuming that the layer thickness is small compared with the wavelength, the linear slip interface theory can be used to solve the problem. The insight gained from this analysis is that, in addition to acoustic impedance, crack abundance (i.e., crack density) and fluid properties (water, oil, or gas) significantly affect the wave reflection amplitude. Higher crack density and lighter fluid (i.e., gas) will substantially increase the reflection intensity, generating “bright spots” in reflection surveys. The theoretical result has been verified by a deep well acoustic reflection imaging case study. The results can be used to provide a “bright spot” exploration technology for fractured oil and gas reservoirs.
Paper Information:
Tang X, Wang W, Wang H, Zheng K. 2025. Elastic-wave reflection “bright spot” of a fractured rock formation: Theoretical analysis and deep-well acoustic imaging evidence. Science China Earth Sciences, https://doi.org/10.1007/s11430-025-1674-6
