Study Of Seismic Attributes For The Discontinuity Of Channel Sandstone Reservoir

Discontinuity boundaries are common in the channel sandstone reservoir such as structural faults and sedimentary interbedded sandbody interfaces.The discontinuity boundaries can directly influence the fluid flow.This also could influence the distribution of remaining oil and the relationship of injection-production and could affect exploitation efficiency.Therefore,the accuracy of discontinuity boundaries identification is related to the success rate of development well location identification.The type of sandstone discontinuity boundaries is related to the mode of interbedded sandbody configuration.Investigators domestic and abroad have studied the mode of interbedded sandbody and have constructed interbedded sandbody model,and further performed seismic forward modeling,waveform response analysis and seismic attributes analysis for sandbody discontinuity boundaries study.However,most theoretical studies are not comprehensive enough.The type of sandstone boundaries is simple.The type of seismic attributes lacks of full ranges of study,particularly lacks of study under seismic noises.In the recent years,exaction of seismic discontinuity attributes has been an effective method to detect the discontinuity boundaries.However,these discontinuity attributes are normally used to detect large scale fault.This leads to that the attributes are barely used to to detect small scale interbedded boundaries.Therefore,there is a need to use the sandbody boundaries model to study the detectability of interbedded boundaries using seismic discontinuity attributes.In addition,due to sparse wells in the offshore oilfield,it has become a practical issue on how to make full use of seismic data to describe the spatial distribution of discontinuity boundaries in channel sandstone reservoir.In this work,the mode of interbedded sandbody configuration is summarized.The velocities and densities of sandstones from Qin Huangdao area are suited to construct a 3D interbedded sandbody boundaries model.The constructed model considers various types of discontinuity boundaries with different lateral separation and vertical depth difference for channel sand,abandoned channel and overbank sands.The convolution method was used to the forward modeling of 3D interbedded sandbody boundaries model for seismic response analysis.The characteristics of seismic waveform is further analyzed and summarized in the interbedded area.42 different seismic attributes including amplitude,complex trace,spectral,waveform and nonlinear type of attributes are extracted and analyzed.Then,selected 20 seismic attributes which sensitive to sandstone boundaries,interbedded area and vertical depth differences are further analyzed for their anti-noise ability.Random noises commonly exists in the field data.The attributes along horizons from field data can be interfered with noise for the depiction of discontinuity boundaries.Therefore,the median filter,the trimmed-mean filter,the modified-trimmed-mean filter,the multistage-median filter,the multistage-median modified-trimmed-mean filter,the edge-preserving smoothing filter and the anisotropy diffusion filter are analyzed and compared.Finally,we proposed a modified edge-preserving smoothing diffusion filter method for noise removal.The data test results showed that the edge-preserving smoothing diffusion filter not only is effective to remove the random noises but also can enhance the characteristics of energy distribution of seismic attributes.The processed attributes showed clearer boundaries of geological body.In this work,a 2D interbedded sandbody model is further constructed.The detectability of interbedded boundaries by C1 coherence,C3 coherence,local structural entropy,gradient structural tensor and 3D curvature are analyzed and compared.The results showed that the local structural entropy is the best attribute for the boundary identification.Combining the features of local structural entropy and gradient structural tensor,a dip-oriented gradient-energy-entropy coherence is proposed.A 2D small-scale fault model is constructed to verify its advantage to the anti-noise ability and the detection of small-scale discontinuity.Finally,the proposed methods were used to the channel sandstone reservoir in the Qin Huangdao area.Three type interbedded sandbody boundaries were identified.These are tightness contact,loose contact,and scatter contact.Proposed attributes are extracted including C3 coherence,local structural entropy and gradient structural tensor,dip-oriented gradient-energy-entropy,max positive curvature and min negative curvature.The comparison study showed that,the gradient structural tensor and the dip-oriented gradient-energy-entropy are the better attributes for the identification of vertical discontinuity boundaries.Meanwhile,by comparing the selective 20 sensitive attributes sensitive to lateral discontinuity boundaries,it is found that 10 sensitive attributes can preferably response the lateral distribution characteristics of channel sandbody.Furthermore,application of oriented filters,RGB fusion,and K-L transform to these attributes can enhance the boundaries characteristics.The study demonstrated a technique flow for the identification of discontinuity boundaries for the channel sandstone reservoir.Also,Reservoir Discontinuity Prediction Software is developed,which can be used to solve the problem in practical production.