三维叠前转换波克希霍夫时间偏移方法研究

Research on Kirchhoff time migration for 3-D prestack converted wave

(1.成都理工大学“油气藏地质及开发工程”国家重点实验室,四川成都610059；2.中国石油勘探开发研究院西北分院,甘肃兰州730020)

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China

在地层含气时，转换波勘探可以获得更为丰富的地下信息。但由于转换波的射线路径不对称，因此转换波的叠前偏移比纵波复杂。在VTI介质中，三维叠前转换波克希霍夫时间偏移的旅行时受偏移孔径、速度模型和双程垂向旅行时等多种因素的影响，为此，对转换波旅行时的计算方法和偏移算法进行了讨论。转换波旅行时由激发点到成像点的纵波旅行时和成像点到接收点的转换波旅行时两部分构成，通过建立旅行时表来提高偏移计算效率，保证旅行时精度。同时，讨论了基于VTI介质的三维转换波叠前时间偏移近似算法，利用理论模型验证了叠前时间偏移方法的正确性。对西部某油田实际转换波地震资料进行三维叠前时间偏移的结果与井资料较为吻合，含气地层的成像优于纵波。

Converted wave exploration can obtain abundant information in gas-bearing horizon. The pre-stack migration of converted-wave is more complex than that of P-wave because the ray paths of the convertedwave are asymmetry. In VTI media, the travel time of 3-D pre-stack Kirchhoff time migration for converted-wave is affected by many factors, including migration aperture, velocity model, and two-way vertical travel time. Aiming at this problem, we discussed the calculation method and migration algorithm of converted-wave travel time. The travel time includes the P-wave travel time from the source to imaging points and the converted-wave travel time from imaging points to receivers. The travel-time form is established to improve the migration computation efficiency and guarantee the accuracy of travel time. In addition, we also discussed the algorithm for 3-D pre-stack time migration of converted-wave in VTI media. The validity of pre-stack time migration method is verified by a theoretical model. The 3-D pre-stack migration result of one actual converted-wave data from a certain oilfield in west area matches its logging data very well and the imaging effect in gas-bearing horizon is better than that of P-wave.