Prediction Of Sandbody And Sedimentary Facies Analysis Of Shanxi Formation In Yichuan Area Of Ordos Basin

Shanxi Formation in Yichuan area is meandering-river delta front sub-facies with shallow water depth and sufficient provenance supply,which results in strong lateral heterogeneity of sandbody.It is difficult to predict distribution of sandbody and sedimentary facies by traditional logging methods under large well spacing in the study area,so that the drilling success rate is low.And the strong reflection formed by coal seams and carbonate stratigraphic in the study area weaken the effective reflection of sandbody,which affects the effect of using seismic data to predict distribution of sandbody.Base on the above problems,this study use combination of core,logging and seismic data.The method of"well-seismic combination and multi-dimensional interaction"is adopted to carry out the fine interpretation of three-dimensional structure,through which the formation pattern and structural characteristics are clarified.Then,the prediction ability of frequency-divided seismic attributes fusion technique and frequency-divided inversion method for the target layer sandbody is compared,the method of"multi-wavelet decomposition and reconstruction technique combined with frequency-divided inversion"was selected,and on this basis,the probability model of sandstone is established to predict the distribution of sandbody.Finally,the sedimentary facies analysis is completed by using the research idea of"well seismic combination,model guidance and multi-dimensional interaction".The research results improv the prediction accuracy of sandbody and sedimentary microfacies prediction,lay the foundation for the development of tight sandstone gas reservoirs in the target layer,and provide experience for the prediction of sandbody distribution by well seismic methods under strong reflection background.Research shows that:(1)The structural type of the target stratum is monocline with low gradient and no faults,and its northwest region is relatively low;The horizontal distribution of stratum is stable and its pattern is aggradation type;(2)The main reasons why it is difficult to predict sandbody by frequency-divided seismic attributes fusion are reservoir properties,the decay in frequency of seismic wave as it propagates,and the superposition of reflection wavelets leads to the complexity of seismic information;(3)If strong reflection exists in the formation,the multi-wavelet decomposition and reconstruction technique can improve the effect of frequency-divided inversion to predict the distribution of sandbody.(4)If there is little difference between the wave impedance of sandstone and that of mudstone,the frequency-divided inversion method has better ability to predict the distribution of sandbody compared with the conventional wave impedance inversion methods.(5)The width of sandbody is large,and the distribution patterns is mainly cross-cutting banded form and isolated banded form.The development degree of sand body of each layer is different,and the development degree of sandbody of Shan 2~2 layer is the least.(6)The distribution patterns of underwater distributary channel include cross-cutting banded form and isolated banded form;The sedimentary period of Shan 2~2 is in the middle period of the medium-term cycle,so the development degree of its underwater distributary channel is relatively poor.(7)The sedimentary microfacies superimposed styles include underwater distributary channel-interdistributary bay-underwater distributary channel type(interval type)and underwater distributary channel-underwater distributary channel type(contact type).