--> ABSTRACT: Numeric Simulation of Frequency-Dependent Seismic Response and Hydrocarbon Detection, a Turbidite Reservoir in JZ Area, the Bohai Sea, China, by Chen, Xuehua; He, Zhenhua; He, Xilei; Huang, Deji; #90142 (2012)

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Numeric Simulation of Frequency-Dependent Seismic Response and Hydrocarbon Detection, a Turbidite Reservoir in JZ Area, the Bohai Sea, China

Chen, Xuehua*1; He, Zhenhua1; He, Xilei1; Huang, Deji2
(1) State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, China. ([email protected]
(2) College of Geophysics, Chengdu University of Technology, Chengdu, 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