孔洞型碳酸盐岩储层地震正演及叠前深度偏移

塔里木盆地孔洞型碳酸盐岩储层具有尺度小、埋藏深、非均质性极强的特征,严重制约油气的勘探开发。针对碳酸盐岩储层的复杂性和特殊性,有必要开展地震正演模拟和叠前深度偏移方法优选研究。基于PML边界的变网格高阶有限差分算法可对小型非均质地质体进行精确地震模拟,既保证了模拟精度,又提高了计算效率,为理论研究提供模拟数据。采用克希霍夫积分法、单程波、逆时偏移对模拟数据进行偏移成像。结果表明,在速度准确情况下,波动方程方法成像效果优于积分法成像,实际资料也验证了这一点;从保幅角度来看,单程波偏移方法的振幅相对保持能力最佳,优于积分法和逆时偏移。综合上述3种偏移方法的成像效果、计算效率和振幅保持能力,单程波叠前深度偏移更适合孔洞型碳酸盐岩储层的成像。

Seismic forward modeling and pre-stack depth migration of porous-type carbonate reservoirs

The porous-type carbonate reservoirs in Tarim Basin are characterized by small scale, large buried depth and extremely strong heterogeneity, severely restricting hydrocarbon exploration and development. Aiming at the complexity and specialty of carbonate reservoirs, it is required to carry out the optimization research on seismic forward simulation and pre-stack depth migration method. PML-boundary-based variable-gird high-order finite difference algorithm can be used to conduct precise seismic simulation on small heterogeneous geologic bodies, which can not only guarantee simulation precision, but also improve computational efficiency, thus providing simulation data for theoretical research. Then, Kirchhoff integral method, one-way wave and reverse-time migration methods are applied for the migration imaging of simulation data. The results have shown that in case of accurate velocity, the imaging effect of wave equation method is better than the integral method, which has been also validated by actual data. In terms of amplitude preservation, the one-way wave migration method has better relative amplitude maintained capacity than the integral method and reverse-time migration method. Considering the imaging effect, computational efficiency and amplitude maintained capacity of the above three methods, one-way wave pre-stack depth migration is more applicable to the imaging of porous-type carbonate reservoirs.