复杂地表浅层速度建模技术研究及应用

A shallow velocity modeling technique for complex surfaces

随着中国西部复杂山地油气勘探程度的不断深入,真地表叠前深度偏移技术的重要性不断提升,但该技术的应用效果不理想,除整体速度模型精度不够的固有因素外,近地表速度模型与时间域静校正的关系、层析成像方法和偏移策略也是影响真地表叠前深度偏移应用的关键因素。针对这种情况,分析了目前叠前深度偏移处理中地表圆滑偏移基准面与浅层速度建模存在的问题,提出了适合复杂山地的真地表浅层速度建模技术。首先通过微测井约束回折波分层层析反演建立准确的深度域近地表速度模型,避免时间域静校正对实际地震波场的改造;然后在井控地质导向约束下,通过包含高精度旅行时算法的各向异性多方位层析反演迭代,使得浅层以及中、深层深度偏移速度模型更准确;最后利用TTI逆时偏移实现真地表叠前深度偏移。该技术的核心思想包括微测井约束下的初至回折波层析反演、真地表偏移基准面选取和数据校正的综合应用。实际复杂山地地震资料应用结果表明,该技术有效提高了速度模型精度,提高了断裂及构造成像质量,较好地解决了井震深度误差,为复杂山地油气勘探提供了有效的技术支撑。

With the development of oil and gas exploration in complex mountainous areas of western China,true-surface pre-stack depth migration is becoming increasingly important.In addition to the velocity model,the relationship between the near-surface model and the time-domain static correction,tomographic imaging method,and migration strategy are key factors affecting the real-surface pre-stack depth migration.After analyzing the issues associated with the smoothed-surface migration datum and the shallow velocity modeling in the pre-stack depth migration,a true-surface shallow velocity modeling approach that is suitable for complex mountainous areas is proposed.Firstly,the accurate near-surface velocity model in the depth domain was established by refraction tomography inversion using an up-hole survey constraint,thereby avoiding the time-domain static correction on actual seismic wavefields.Then,under the constraint of well-controlled geological guidance,the anisotropic multi-directional tomography iteration technique with highly precise calculation of the travel time was adopted to produce an accurate migration velocity model for shallow and intermediate depths.Finally,reverse time migration based on the tilted transverse isotropic acoustic wave equation was utilized to achieve the true-surface pre-stack depth migration.Key aspects of the proposed technique are the comprehensive application of the first-arrival tomography inversion with the up-hole survey constraint,near-true surface migration datum,and data correction.A practical application on a complex mountainous area demonstrated that the use of the proposed technique improved the velocity accuracy and the quality of fault and structural imaging,and solved the inconsistency between wells and seismic data,thereby aiding the oil and gas exploration in complex mountainous areas.