基于模型约束的Kirchhoff积分法叠前深度成像

Pre-Stack Depth Migration Based on Model Confined Kirchhoff Integration

与时间域偏移方法比较,叠前深度偏移成像方法能够适应剧烈横向速度变化、陡倾角反射的地震资料。本文通过研究Kirchhoff叠前深度偏移方法成像原理,首先建立初始速度模型;然后在初始速度模型中加入了目标地质体——盐丘作为层位,对初始速度模型进行优化,在层位的约束下通过多次迭代计算,对优化前后的两个速度模型求取旅行时差更新初始速度模型;最后利用更新后的初始速度模型进行Kirchhoff积分法叠前成像。叠前时间偏移和模型约束下的Kirchhoff积分法叠前深度偏移成像结果显示,后者成像具有更高的信噪比和分辨率。

To compare the pre-stack migration in the time domain(PSTM),the pre-stack migration in the depth domain(PSDM)can adapt to the seismic data which has the high dip angle and the large variation of the velocity in the horizon.Based on the imaging principle of Kirchhoff pre-stack depth migration method,we established the initial velocity model at first;then added the target geological body-Salt Dome to the initial velocity model,and further optimized it;under the constraints of the horizon of the salt dome,we computed the difference of two travel times through a lot of iterations so as to update the initial velocity model.By the updated initial velocity model,the Kirchhoff integral method is used to migrate the seismic data.The job can be finished if the corrected reflection phase of the common imaging point gather is at the same level;if not,the horizon of the salt dome has to be modified again and again.We can modify the horizon by use of the well logs and the geological knowledge or consult with the geological experts.Taking this new modeling approach,the latter image has higher S/N and resolution compared to the results of the PSTM imaging methods under the constraints of the horizon of the salt dome.The specific performance is the clear breakpoint,outstanding wave group characteristics;especially,the outline of the salt dome has very clear boundaries,and the bottom of the salt dome image is also much more improved than that of the image of the PSTM.