Near-surface Q compensation for absorption and dispersion in pre-stack time migration from topography

In some areas containing loose near-surface medium and irregular topography, the high resolution seismic imaging results, which are critical for oil exploration, while always very hard to obtain. The pre-stack time migration from topography (topography PSTM) handles the irregular topography problem by using two effective velocity parameters. However, the resolution of seismic imaging is still mainly degraded due to the absorption and dispersion caused by the intrinsic attenuation of the near-surface medium.

In order to address this issue, this study presents a near-surface Q compensated direct migration scheme by introducing a near-surface effective Q parameter to improve topography PSTM, called near-surface QPSTM. The introduced near-surface effective Q parameter is related to lateral coordinates for each receiver rather than a commonly used Q factor, thus the effective Q parameter can be estimated by scanning the imaging gathers of common receiver group, and then the Q field can be obtained by fitting a relationship between the near-surface effective Q and the velocity parameters. The main advantage of the near-surface QPSTM over conventional statics corrections plus inverse Q filtering is that it honors the actual wave propagation path instead of using a vertical travel time in the near-surface medium, and compensates for absorption and dispersion during migration. Besides, it can update or build the near-surface Q model by using the surface reflection seismic data during migration without detailed near-surface velocity and Q models provided in advance.

We used a simple synthetic example to verify the correctness and effectiveness of the near-surface QPSTM. More accuracy and higher resolution of migration results obtained by the near-surface QPSTM than the conventional PSTM are gained on a real data example from oil field. The higher resolution seismic imaging results can service the oil exploration and production.