Evaluation Of Reservoir Connectivity Based On Frequency Dependent Attributes

Permeability is an important property of reservoir,which can represent the connectivity of reservoir and the ability of fluid flow,and play an important role in the the study on distribution of fluid and oil and gas exploitation.The imaging attribute and reservoir fluid mobility extracted from the low-frequency seismic signal contains reservoir permeability and fluid viscosity coefficient information;1 attribute combined with the seismic high frequency signals and low frequency signals can reflect connectivity of fractured reservoirs.Therefore,the application value of imaging attributes,reservoir fluid mobility and 1 attributes has been paid more and more attention.The common used imaging attribute and reservoir fluid mobility plays an important role in the prediction of reservoir physical parameter and fluid parameters,but the method in the reservoir fluid flow capability evaluation have many uncertainty and ambiguity,as the following two aspects: 1.influence of lens in the reservoir,calculation formula of imaging attribute and reservoir fluid mobility from frequencydependent reflection coefficient,this reflection coefficient only considering the reflection on the interface,and the actual seismic reflection signal not only is the seismic wave at the interface of reflection,also contains the reflection information within the reservoir multi lens layers.2.the optimal frequency,optimal frequency is important for the calculation of imaging attribute and reservoir fluid mobility,the commonly used method is the artificial selection,so that attributes human disturbance factors extracted from the larger,not reflect the reservoir fluid activity.Aiming at the above problems,this paper based on rock physics,discusses the applicable conditions of conventional reservoir fluid mobility and 1 attributes;considering the reflectivity of the permeable inhomogeneous layer,solves the problem of selecting the optimal frequency,eliminate the influence of interbedded reservoir,the main content of the work and understanding are:(1)Introduced theory of frequency-dependent reflectivity from a fluid-saturated poroelastic medium,analyzed the relationship between the frequency-dependent reflectivity coefficient and permeability,viscosity coefficient and frequency.On the basis of the above research,the paper compares the advantages and disadvantages of imaging attribute and reservoir fluid mobility.(2)We presents the characteristics analysis of reservoir fluid mobility and 1 attribute with change of permeability in use of numerical simulation based on dualporosity model.The result show that phase velocity of seismic wave can be influenced by permeability,which can cause the phenomenon of attenuation and dispersion,and at the dispersion phenomenon of the low frequency is more obvious than the high frequency.It is concluded that the two attributes are significantly proportional to permeability,in the first model the acoustic impendence contrast between the top layer and the reservoir decreases with the increase of permeability.In the second model that acoustic impendence contrast between the top layer and the reservoir increase with the increase of permeability,reservoir fluid mobility is generally proportional to permeability,1 attribute is generally inversely proportional to permeability.Then take the offshore oil well A carbonate reservoir zone as an example,the author estimated the connectivity in this area by using reservoir fluid mobility attribute and K1 attribute calculation from post stack seismic data combined with geological data and drilling data,It is concluded the result is roughly corresponding to the actual logging data and this method can effectively reflect the permeability distribution in this region.(3)Introducing the reflection coefficient of the permeable inhomogeneous layer,numerical simulation variation of the reflection coefficient with the frequency and the layer thickness.From the point of reflectivity of the permeable inhomogeneous layer,re calculation formula of reservoir fluid mobility,reduced the influence of layer thickness.