| Nowadays,hydraulic fracturing has become one of the important means for the development of oil and gas fields.However,the development of underground fractures cannot be obtained directly during construction.Therefore,microseismic monitoring technology is used to evaluate fracturing effects.Microseismic monitoring is an important monitoring method for hydraulic fracturing transformation of underground reservoirs,and its application prospects are becoming more widespread.However,the source excitation mode of microseismic induced by hydraulic fracturing is more complicated,therefore,the high-order staggered-grid finite difference method is used to simulate the hydraulic fracturing microseismic data and analyze its wavefield characteristics and source radiation characteristics.And based on the understanding of the microseismic wavefield characteristics and source radiation characteristics,this article has carried out a series of applied researches on microseismic observation systems,denoising,and microseismic event location.The details are as follows:(1)Three-dimensional hydraulic fracturing microseismic forward modeling.In this paper,the finite-difference method of staggered grids is used to solve the elastic and viscoelastic wave equations,and the forward modeling of three-dimensional hydraulic fracturing microseismic data is completed.The boundary reflections are absorbed and attenuated by using PML absorption boundary conditions.And using the multi-layer and complex velocity model to verify the forward results;(2)Research on forward simulation of hydraulic fracturing microseismic based on different focal mechanism.Because the source excitation mode of microseismic induced by hydraulic fracturing is more complicated,the source mechanism was introduced.Microseismic forward modeling is based on three different focal mechanisms(ISO,CLVD,DC),and two different methods of source loading are used.By comparing and analyzing the seismic records and the snapshots of the wavefield at different times,The wavefield characteristics and source radiation characteristics under different focal mechanisms were obtained,which provided a theoretical basis for analyzing the influence of the focal mechanism on the positioning accuracy;(3)Research on application of surface microseismic data denoising method.Due to the low signal-to-noise ratio of surface microseismic data,this paper uses simulated microseismic data with different proportions of actual noise By denoising the data containing different proportions of actual noise,we tested the feasibility of the method of denoising surface microseismic data and this method has a good application effect on actual data;(4)Analysis of the influence of positioning accuracy of microseismic events.The forward modeling data is used to analyze the location accuracy of microseismic events,theoretically analyzes the influence of the type of observation system,aperture,spacing,etc.on the positioning accuracy,and also analyzes the influence of stratum absorption and attenuation and focal mechanism on the positioning accuracy.It can provide theoretical basis for actual micro seismic data acquisition,positioning and so on;(5)Practical application of actual microseismic monitoring data in the field.Combining the processing and positioning effect of the three-dimensional microseismic forward simulation data,and complete the processing and positioning of the field actual microseismic monitoring data. |
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