Research And Application Of Cross-well Seismic Reflection Imaging In Karst Exploration

In recent years,associated with underground space development and utilization of underground space and safety operation has become an important task to large and medium-sized cities in China,the detection results of underground space and accurately is the key to guarantee the project successful implementation.Urban underground space probe's main goal is to achieve 200 m underground to shallow rice and Amish target body and structure detection.By cross-hole seismic exploration we can effectively detect underground strata structure,to detect abnormal body size,shape and spatial distribution,etc.,and the results combined with drilling results,but there is scope of exploration is limited,the problem of high cost.By using interwell reflection wave cross-hole,underground and near the well structure imaging,can more comprehensive understanding of two Wells around underground strata structure,to solve the urban geological problems have very important significance.Interwell seismic reflection wave imaging is one of the key steps in crosswell seismic data processing technology,and it is also an effective means to invert geological models.In this paper,numerical simulation is used to realize the inter-well reflection wave migration imaging and the cross-well side reflection wave equivalent imaging.It is necessary to establish a stratigraphic model,simulate the interwell seismic data,analyze the wave field characteristics of the simulated data,and study the extraction of well reflections.The method of side reflection waves.The separated interwell reflection wave is used as the offset velocity model according to the inter-well CT imaging result,and the inter-well reflection wave prestack depth migration is performed;the inter-well side reflection wave is extracted to perform equivalent imaging of the inter-well side reflection wave,and the essence is passed The geometric relationship transforms the original well problem into ground-excited ground receiving problem.The detection point in the well is equivalent to the wave surface reflection path to a certain horizontal surface of the surface interface,and the position coordinate conversion is performed to obtain the relative position of each equivalent point and travel.At the time of change,the ground imaging method was used to image the underground geological anomaly,and the imaging accuracy was studied and analyzed.At the same time,the above method is applied to the engineering problem,the inter-well seismic data in the project is analyzed,and representative data is selected to extract the inter-well reflection wave,carry out the pre-stack depth migration,and study the imaging of the interwell interface and karst.The effect is to extract the reflected wave between the wells and perform equivalent imaging of the reflected wave between the wells to study the imaging effect on the well karst.Finally,the results are analyzed and the following two conclusions are obtained:(1)The pre-stack depth migration method is more accurate for the location of the stratigraphic interface.The detection of geological anomalies such as caves is accurate in the depth range.The lateral resolution of the anomalous body is limited.(2)The inter-well side reflection wave imaging can accurately image the well-side interface and the low-speed anomaly.Selecting the equivalent velocity is the key factor affecting the imaging result.This paper use crosswell seismic reflection wave prestack depth migration and side equivalent reflection wave imaging method for imaging analysis of actual seismic data,good results have been achieved.Therefore cross-borehole reflection wave imaging method is practical and effective.