长宁页岩气开发随钻跟踪叠前深度偏移建模方法及应用效果

Modeling method for prestack depth migration and tracking while drilling in shale gas development and its application effect in Changning

受多期次构造运动影响,四川山地探区地表起伏剧烈,相对高差大;近地表低降速带结构复杂,局部区域有高速岩层出露;地下构造复杂,各向异性问题突出。为此,以长宁页岩气勘探开发工区水平井随钻跟踪处理为例,针对复杂地表及复杂地下构造的“双复杂”地震资料叠前深度成像,以融合近地表速度的“真”地表各向同性速度精细建模和逐层TTI各向异性速度建模为基础,随钻跟踪中通过井平台滚动处理的模式,以地震数据驱动为主,及时利用已钻井信息约束,同时通过多角度、全方位地震—地质一体化地质因素分析对速度模型修正提供指导,提高了速度模型精度,减少了深度域速度的多解性,使得复杂构造成像更贴合地下真实地层产状,最大限度地满足了随钻跟踪对水平井段地层产状预测准确性和对资料处理时效性的需要。

The terrain of the mountainous exploration areas in Sichuan Province is usually complex.Specifically,affected by multi-stage and multi-group tectonic movements,the undulating surface varies rapidly,with large relative relieves.The near-surface low-velocity and sub-weathered zones are structurally complex,and high-velocity rock strata outcrop to the surface in certain regions.The underground structures are also complex with salient anisotropy.For the above reason,this paper discusses the seismic data processing for tracking while drilling of horizontal wells in the shale gas exploration and development area as an example in Changning.The prestack depth imaging of the seismic data on the“dual complexities”of complex surface and complex underground structures is investigated.Isotropic fine velocity modeling on the“true”surface and layer-by-layer tilted transversely isotropic(TTI)anisotropic velocity modeling for near-surface velocities are integrated.During tracking while drilling,the mode of rolling well platform processing is adopted.The procedure is mainly seismic data-driven,but information on drilled wells is used as constraints in a timely manner.Moreover,comprehensive geological factor analysis featuring seismic-geological integration from multiple perspectives is conducted to guide velocity model modification.As a result,the accuracy of the velocity model is enhanced,and the non-uniqueness of velocities in the depth domain is reduced.Furthermore,the imaging of complex structures is more consistent with the real underground stratigraphic occurrence.The proposed method meets the requirements of tracking while drilling on the accuracy of stratigraphic occurrence prediction of horizontal sections and the timeliness of data processing.