优势方位地震数据在多尺度断裂识别中的应用

Application of dominant azimuth seismic data in multiscale fracture identification

目前针对页岩油气、致密油气等低效产层的开发主要通过水平井钻探实现,水平井钻遇中、小尺度断层时容易发生垮塌、卡钻和漏失等工程事故,严重影响开发效率。因此,精细预测断层的展布是急需解决的问题。常规方法依据地震波在HTI介质不同方向传播过程中表现的速度、振幅、走时等参数的特征差异,利用垂直断裂走向的部分方位叠加数据识别断层,但复杂构造带断层的走向复杂多变,常规分方位叠加方法无法实现叠加道集方位与所有的断层都垂直。为此,提出应用“两宽一高”道集数据进行OVT域偏移处理,根据其速度、振幅以及走时等参数变化,自适应地提取地下每一点对应的受断裂影响最大的方位道集,重构形成断裂优势方位地震数据体。自动提取的垂直断层走向的道集(或叠加)数据不仅适用于多期次、多方向的复杂断裂发育区,还能进一步提高断层预测的精度,使断裂刻画尺度更小、细节更丰富,预测结果为水平井导向和压裂设计提供了依据。

At present,the development of low-efficiency production layers such as shale and tight oil&gas reservoirs is mainly realized by horizontal well drilling.However,when small and medium-sized faults are encountered during the drilling,engineering accidents such as collapse,sticking,and leakage are easy to occur,which will seriously affect development efficiency.Therefore,the accurate prediction of fault distribution is an urgent problem to be solved in production.According to the knowledge of the characteristics of velocity,amplitude,travel time,and other parameters in the propagation of seismic waves in different directions in HTI media,the conventional method uses partial azimuth stacking data of vertical fracture strikes for fault identification.However,the fault strikes of complex structural zones are complex and changeable,and the conventional azimuth stacking method cannot ensure the gathers are perpendicular to all faults.Therefore,we propose to use the gather data of“wide azimuth,broadband,and high density(WBH)”for OVT domain migration processing.The azimuth gather corresponding to each underground point most affected by a fault is adaptively extracted according to the changes in velocity,amplitude,and travel time,so as to reconstruct the dominant azimuth seismic data volume of the fracture.The gathers(or stacking data)perpendicular to the fault strike can be applied to the complex fracture development areas with multiple stages and directions,and lead to a smaller scale and richer details of fracture characterization,as well as higher accuracy in fault prediction.The predictions can provide a basis for horizontal well guidance and fracturing design.