Forward Modeling Study Of The Time-frequency Response Law Of Thin Interbeds With Random Thickness Distribution

With the deepening of oil and gas exploration and development,the study of thin interbedded oil and gas reservoirs in sand mudstone has been paid more and more attention,which are characterized by thin sand body,weak reflection,and large randomness in the combination of thin layers.The geological model of thin interbedded reservoirs with random thickness distribution is more general,and the seismic data after forward simulation is closer to the actual seismic data,which makes the study more general and is a key area for future research on the forward simulation of thin interbedded reservoirs.However,there are three problems in the study of thin interlayer with random thickness distribution: first,there is a lack of a geological modeling method for random thickness distribution thin interlayer that can randomly simulate the lithological conversion of sedimentary sequences;second,there is a need to find a high-precision time-frequency analysis method that is applicable to the detection of weak signals in thin sand bodies;third,the characteristics of time-frequency response and variation law of thin interlayer with random thickness distribution are still unclear,and it is urgent to carry out Targeted research is needed.In this thesis,we firstly introduce Markov chain theory into the geological modeling of thin interlayer to generate lithological profiles with randomly varying thickness and position,and then establish a geological modeling method for thin interlayer with random thickness distribution.Secondly,a comparison of the processing effects of time-frequency analysis methods is carried out to select a method suitable for the detection and analysis of timefrequency characteristics of weak reflection signals in complex geological backgrounds,so as to accurately characterize the transient spectrum of thin interlayer with randomly distributed thickness.Third,since the orthorectified simulation of thin interlayer is an important research tool for the study of thin interlayer.Therefore,this thesis adopts the fluctuation equation orthorectified simulation method to obtain the simulated seismic data of the geological model of thin interlayer with random thickness distribution,and adopts the second-order simultaneous extraction transformation algorithm to obtain the instantaneous spectrum of the reflected composite wave,and then examines the characteristics and variation law of the time-frequency response of the thin interlayer with random thickness distribution and different minimum unit thicknesses.Through a large number of thickness randomly distributed thin mutual layer orthorectified simulation analysis and processing results to obtain the following points of understanding:(1)The Markov chain is used to establish the geological model of the thin mutual layer with random thickness distribution,which can better reflect the original depositional characteristics of the thin mutual layer reservoir in sandy mudstone and is an effective method for geological modeling of the thin mutual layer with random thickness distribution.(2)The time-frequency spectrum of the second-order synchronous extraction transform has the characteristics of good energy focus and high time-frequency resolution,which is very suitable for the detection and analysis of the time-frequency characteristics of weak reflection signals such as thin layers and equivalent thin layers.(3)In the time-frequency domain,the main frequency line in the second-order synchronous extraction transformed time-frequency spectrum follows the overall change law of "thin rise and thick fall" along the frequency direction;in the calculation result of the operator,the "arch" shape in the range of 50-100 Hz indicates the thickness of the small layer.The "arch" pattern in the range of 50-100 Hz indicates the thickness of the small layer;the "inverted arch" pattern below 50 Hz indicates the position of the equivalent thick layer;the "X" pattern above100 Hz indicates the position of the thick layer,and these three aspects give a good picture of the internal details of the thin mutual layer with random thickness distribution.(4)Combining the excellent characteristics of various time-frequency analysis methods,the top-bottom interface is determined by the second-order synchronous extraction transform,the overall thickness change trend is determined by the generalized S-transform combined with the synchronous extraction transform,and the internal structure is determined by the secondorder synchronous extraction operator feature,which accurately portrays the characteristics and change law of the time-frequency response of the thin mutual layer with random thickness distribution.The above research is of great significance to enrich the geological understanding of thin interlayer and promote the research work of thin interlayer.