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Numeric Simulation of Frequency-Dependent Seismic Response and Hydrocarbon Detection, a Turbidite Reservoir in JZ Area, the Bohai Sea, China
The numerous recent laboratory and field examples show the
potential benefits of seismic low frequencies in hydrocarbon detection. To
simulate the frequency-dependent response of turbidite reservoirs in JZ Area,
the Bohai Sea, China, and then implement frequency-dependent detection of the
hydrocarbon accumulation based on low frequencies, we expanded a diffusive and
viscous wave equation (DVWE), which takes into account the diffusive and
viscous attenuation, and velocity dispersion in fluid-bearing poroelastic
media. In design of reservoir equivalent geologic model, by applying a
90°-phase shift on the raw seismic section contained turbidite, we pick
zero crossing on converted section to produce interface (reflectivity) section.
Then assigning the parameters such as density, velocity, diffusive and
viscosity, and Q for each stratum produce physical parameters section. Such
parameters originate from the well log and rock physical experiments. The DVWE
based simulation result not only shows the characteristic reflection and
geometry of turbidites, that are consistent desirably with the reflection
feature on the raw seismic section, but also delineates the phase delay,
instantaneous dominant frequency decrease and magnitude attenuation related to
the gas-bearing reservoir. By conducting instantaneous spectral decomposition
on the simulation section, the common frequency section indicates bright
strong
energy of the gas reservoir and low-frequency shadow lie immediately underneath
the reservoir at 8Hz and 12Hz. At 20Hz and 28Hz, the gas reservoir is brighter
than the shadow that becomes weaker but still persists. The shadow is almost
gone at 36Hz.
We carry out
instantaneous spectral decomposition and calculate fluid mobility (permeability
to viscosity ratio) on the seismic data. At 12Hz, the hydrocarbon accumulation
in tubidite show clear bright
spot on common frequency section and horizon
slice at the reservoir. There show abnormally strong low-frequency shadow on the
common section and the slice for a 40ms window immediately below the reservoir.
At 20-36Hz, the reservoir remains
bright
, and the shadow gradually disappear.
The fluid mobility calculated at 12Hz also clearly delineates the brighter gas
reservoir and its spatial distribution.
In this case study presented above, the low-frequency effects are especially important for delineate the fluid signature. It is necessary to developed numerous deeper laboratory and theoretical research in the near future.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California