Scattering characteristics in heterogeneous fractured reservoirs from waveform estimation

Abstract

Offset-dependent characteristics of seismic scattering are useful in the interpretation of fractured reservoirs. Synthetic seismograms generated by a 3-D finite difference modeling are used to study elastic wave propagation and scattering in heterogeneous fraetmed reservoirs. We use two models having different background medium properties and different azimuthal AVO responses and build heterogeneous fracture densit)' realizations through stochastic modeling. Gas-saturated fractured reservoirs and waveforms ill fracture normal and strike directions are considered in this paper. The multiple signal classification (MUSIC) frequency estimator is used in waveform estimation to proYid" frequency domain attributes related to seismic wav" scattering by fractmes. Om l"('sults indicate that the strength of the scattered field increases with increasing fracture scatter density and decreasing correlation length of spatial variations of fracture densit,·. It is also a function of the background medium. The strengt h of the scattering field is stronger in model 1 which has smaller property contrasts in the background medium than model 2. The scattering characteristics for both models are different at the top and the base of the fractured reservoir. Our results show that the scattered field is weak at the top of a fractured reservoir. The first order results are dominated by velocit)' anisotropy of a mean crack density field. However, the base of the fractured reservoir corresponds to a strong scattered field on which fracture heterogeneity has a larger effect. 5-1Shen and Toksiiz

Azimuthal offset‐dependent attributes applied to fracture detection in a carbonate reservoir

“…The modeled results also show that the first-order effect of fractures on frequency variations with offset (FVO) and AVO is controlled by the mean fracture density (Shen and Toksoz, 2000). In addition, the study shows that signal frequencies in the crack normal direction decrease faster with offset than those in the crack strike direction.…”

“…Setting aK = 1 for all K leads to the multiple signal classification algorithm (Schmidt, 1986); setting (YK = l / h~ for all K yields the eigenvector algorithm frequency estimator (Johnson and DeGraaf, 1982) where hK is the eigenvector associated with V K . The frequency estimator also is detailed by Shen and Toksoz (2000).…”

Impact of Pre-stack and Post-stack Seismic on Integrated Naturally Fractured Reservoir Characterization

“…Since the early ideas proposed by Crampin 13 et al about the use of pre-stack seismic data to detect fractures, many teams [18][19][20][21][22][23][24][25] have exerted significant efforts to find practical ways to accomplish this. Unfortunately, this area turned out to be a very challenging scientific domain where the solutions seem to be very complex.…”

“…Many of the simplifying assumptions made in the area of fracture detection using azimuthal analysis are not currently needed as extensive work [21][22][23][24][25][26][27][28][29][30][31][32] have improved seismic anisotropy analysis techniques, and fracture "imaging" is possible today without using the common simplifying assumptions. Unfortunately, most of the current providers of this technology are using the simplifying assumptions.…”

Seismically Driven Integrated Fracture Modeling

“…Since the early ideas proposed by Crampin 12 et al about the use of pre-stack seismic data to detect fractures, many teams [17][18][19][20][21][22][23][24] have exerted significant efforts to find practical ways to accomplish this. Unfortunately, this area turned out to be a very challenging scientific domain where the solutions seem to be very complex.…”