Studies On Methods Of Geophysical Prediction In Sand Bodies Of Shallow Water Lacustrine

Lai bei area of lower Minghuazhen formation of Neocene, is shallow water lacustrine basin deposition, with two different characteristics, which contains both features of river and lacustrine. In such sedimentary environments, rapidly lateral changes of reservoirs lead to sand body distribution is hard to control, which restricted the exploration and development of this area. In view of this, the paper through a comparative analysis of conventional sand body prediction method of geophysical, filters out sand body prediction method for shallow water lacustrine basin and subtly depicts the characterization of sand body in the area. The prediction provides reference for objective exploration.Regular sand body prediction technologies include Seismic facies analysis, seismic attributes analysis, and seismic inversion analysis. Seismic Facies analysis technology applies seismic reflection parameters, such as continuity, frequency and amplitude characteristics, combined with the geological information in wells, to recognize sand body through manual or software clustering recognition of sand. Seismic attributes technology based on seismic attributes, can extract lithological information from seismic data, and then convert them into identifiable information associated with rock. At present the main seismic attributes have amplitude statistics class, complex trace statistics, and spectrum statistics class and so on. Through applying the expert experience or mathematical method to screen kinds of attributes, one or several attributes that are the most sensitive to reservoir lithological properties can be gained and sand body is predicted. Post-stack seismic inversion technology mainly includes three kinds of seismic inversion technology, such as the seismic inversion technology based on recursive, the seismic inversion technology based on the model and the seismic inversion technology based on the seismic attributes and so on. with the development of technology and the requirement of the high accuracy, integrating the vertical drilling data with the high resolution with seismic data which has better lateral continuity become an inevitable trend. Seismic inversion technology mainly converts the seismic data that present reflection interface into the data that present rock formation information. Through this method, the results of inversion can be directly compared with drilling, logging, which also can be used to predict change of features of sand body in the underground space.The comprehensive researches based on area actual material have been done to establish isochronous stratigraphic framework. During the research, there are some Strong amplitude-low continuity-low frequency reflection characteristics and weak amplitude-continuity-low frequency reflection characteristics in the bottom of the lower Minghuazhen formation of Neocene, and are overlapped The mutual overlap of the two different kinds of reflection properties up and down is a common phenomenon in the profile of the seismic data. The phenomenon present sand bodies of shallow water lacustrine characteristics of the mutual overlap and succession development. when the clustering software is used to classify the wave forms, the results perform well in local area, but it doesn’t overall. So this method can only be used to predict sand bodies as a auxiliary method; For seismic attribute analysis method, this research used expert experience on attributes to filter, and application results also have validated effectiveness of expert experience. The effective attributes is amplitude attributes and especially are minimum amplitude attribute, square amplitude and so on, these attributes can make seismic anomalous bodies features so obvious that can be described better. For seismic inversion, combination study gave out the result that it cannot be used as main method to describe sand in this research, which due to area that is near1000km2, but the number of well is less, only11, and its distribution is very uneven. What’s more, the anomalous bodies features of shallow water lacutrine basin described by seismic attributes that shows that changes fast on the plan. All elements mentioned above make the accuracy of seismic inversion reduce with limited well constraints conditions.The sand body prediction of ideal technologies-seismic attribute analysis is filtered out, which is on the basis of these studies mentioned above, and anomalous bodies are described well. Firstly, through combination of isochronous formation framework and the interpretation results of Sequence stratigraphy, typical layer segment was selected and selected segment whose top and bottom is PSM1-Ⅲ and To. Secondly, extracted amplitude class of seismic attribute by formation slice, described plane distribution of anomalous bodies, and gave them geological meanings with fine seismic calibration results. Finally, described typical layer segment from three parts, such as plane distribution, profile features and sand thickness, and then chose the best target. Fit statistical regression equation was established between the most effective seismic attribute and sand thickness on wells corresponding to the profile window in this article, and then sandstone thickness were predicted by the seismic attribute.Geophysical methods selected in this article can describe sand distribution and thickness of typical layer segment successfully, and the researches have been verified by manufactures, which indicates that the ideas and methods of this paper are effective.