The Study Of Acquisition Parameters For Crosswell Seismic CT's Image Resolution

Crosswell seismic CT have higher frequency,higher resolution,shorter wavelength and easier required.With the developing of computer technology,the inversion softwares become multifunctional.At present,the technology has been widely used in pile foundation detection and small tectonic investigation.However,the collection parameter design is usually based on experience,instead of theoretical calculation.In this paper,combined with the numerical model and the actual construction situation,from space sampling theorem,the acquisition parameters study of the cross-hole seismic CT detection of karst at limestone region is undertaken.First of all,according to the spatial sampling theorem,the wave number of seismic data is determined by the sampling frequency and the apparent velocity,apparent velocity is related to formation rate,apparent dip,while apparent dip Angle is calculated by the length of well spacing and arrangement.therefore,wave number and negatively correlated with well spacing,formation rate.And array length,sampling frequency were positively correlated.The maximum wave number specified in the sampling theorem is only negatively correlated with the permutation interval.To satisfy the space sampling theorem,the wave number of seismic data is less than the max wave number.In this way,the spacing should be selected according to the spacing of Wells,length of arrangement,formation speed and sampling frequency.On the other hand,the minimum wavelength of the observation system is not larger than the minimum size of the anomalous body,which can effectively distinguish the anomalous body,while the minimum wavelength is determined by the formation velocity and frequency of acquisition.In this way,according to the actual geological prospecting target,each parameter can be measured or calculated to obtain a reasonable interval,which can be selected according to the situation when construction.Secondly,the paper studies the seismic source and the detector.The frequency of collection is the key to determine whether the target is abnormal,and whether the data can contain an effective frequency component is determined by the excitation and receiving device.The paper compares the advantages and disadvantages of various seismic sources,conducts different energy experiments on the point spark source suitable for urban road construction,and studies the characteristics of each energy data.At the same time,the construction conditions and frequency range of four different detectors are compared,which can be selected according to the task.In this paper,the paper studies the correction method of the time of the excitation time of the spark source and the time of the initial recording time of the seismograph.According to the principle of seismic wave ray propagation,the propagation path of the first and the ray in the vicinity of the stratigraphic interface is studied,and the problem of the first arrival of the refraction wave without the formation information is discussed.After the initial arrival of the collection,the reasonable standard of the first to pick up is checked by changing the way set arrangement.In the inversion,the initial model is given by combining the borehole data and the formation velocity,and the influence of the meshing of different sizes on the inversion precision is studied.Finally,through geological exploration task,the acquisition parameters and inversion parameters of the study are applied to the actual project,and the final results obtained are in good agreement with the geological borehole data,and the method is reliable.