Research On Seismic Wave Attenuation And Its Application In Two-phase Media

Petroleum and natural gas occupy an important position in energy exploitation ofmany countries as extremely important natural resources across the world. With theimprovement of petroleum exploration accuracy and target complex degree, theoriesbased on single phase elastic media can hardly solve the problems in new oilfieldexploration and development. Two-phase theory contains the elastic characteristics ofboth solid phase and fluid phase,embodying the subsurface formation porous fluidfilling condition.Consequently, the methods based on two-phase wave theory havemore reasonable rock physics assumptions and are beneficial to discover complexporous oil-gas reservoirs and subsurface fluid.Seismic wave attenuation is an important research field of seismic exploration.Research on seismic wave attenuation in two-phase media is rare.The seismicattenuation characteristic is an important technical means to identify petroleumreservoir. This paper mainly studies the seismic wave attenuation characteristics intwo-phase media with the objectieve to apply the theory results to practicalhydrocarbon detection through the reseach of relationsips between seismic waveattenuation characteristic and the existence of hydrocarbon fluids.Based on the research mentioned above, this paper firstly uses staggered-gridhigh-order finite difference method for seismic numerical modeling. Multiple physicalmodels including heterogeneous media, interbeddings of single and two-phase meida,practical thin reservoirs and isotropic and anisotropic media are established.Two-phase media numerical modeling technology is studied to research the seismicwave propagation and attenuation characteristics in two-phase media from manyaspects.Phase velocity and inverse quality factor are important parameters affectiing the seismic wave propagation and absorption in two-phase media.Under theassumption of plane harmonic wave,the fast and slow P-waves’ analytic expressionsof phase velocity and attenuation are deduced from the Biot P-waves equation inisotropic medium, analyzing the influential law of permeability, viscosity, porosityand other parameters in the vertical direction of wave propagation on phase velocityand inverse quality factor, and compare with BISQ model under the same conditions.The above research in seismic wave attenuation characteristics in two-phasemedia discovered that the low frequency energy of seismic wave is relativelyenhanced but the high frequency energy is relatively weakened. Based on the abovediscovery, this paper proposes the oil revesoir prediction method to detect the seismicdata energy of both high and low frequency.The modeling trial calculation haseffective results. Apply this method on pratical work area target layer of fan131blockES3and get good results thus prove the effectiveness and validity of this method.With these research works, some conclusions can be drawn, as the following:1. Through a series of numerical modeling of two-phase media, the discoverycan be found that both slow and fast waves can generate reflected wave, convertedslow and fast P-wave, converted S-wave, transmitted wave and transmitted convertedwave. Slow P-wave reverses the wave phase in both solid and fluid wave fields. InVTI media, S-wave generates three-bifurcate phenomenon. The shape and size ofthree-bifurcate phenomenon area are related to elastic parameterC13. The wavefrontof fast P-wave has cusps.2. In the routine frequency scale of seismic exploration, the fast and slow P-waveof BISQ model and Biot model do not vary with frequency. In Biot model the phasevelocity of slow P-wave increases significantly along with the increase of frequency.In BISQ model the phase velocity of slow P-wave increases significantly along withthe increase of permeability and the inverse quality factor of the fast P-wave issensitive to the changes of viscosity. In oil-bearing reservoir it is obvious that energyattenuates fast in high frequency but slow in low frequency. The inverse quality factorof slow P-wave velocity of BISQ and Biot model decreases with increasing frequency. 3. Two-phase elastic media has attenuation effect on seismic energy. As a result,seismic wave energy in low frequency is relatively enhanced while it is weakened inhigh frequency. In single phase elastic media has no attenuation effect on seismicenergy. This distinction can be applied to detect subsurface oil and gas. The detectionmethod has good resluts in the practical work erea of fan131block.