面向深层页岩气“甜点”预测的地震勘探技术进展——以DX探区全方位三维地震为例

Recent seismic technology advances for deep shale gas “sweet spot”prediction:A case study on full-azimuth 3D seismic exploration in DX

深层页岩气效益勘探开发需要落实易于压裂求产的“甜点”区,对地震资料成像品质、信息丰度有针对性需求,一是要对与构造保存评价密切相关的断层、断洼以及低序级断裂实现高品质成像,二是要为可压裂性“甜点”预测提供高品质、高精度、高信息丰度的叠前五维地震成像数据。考虑到四川盆地深层页岩气效益勘探对地震资料的针对性需求,重点介绍了地质目标导向的观测系统设计论证与叠前全方位信息保持处理技术及其在綦江高陡构造带DX探区的应用效果。地质目标导向的观测系统设计论证以真地表三维建模及地震正演模拟为基础,通过多维度照明和退化处理分析,设计出满足地质目标探测需求的最优化观测系统。叠前全方位信息保持处理以偏移距向量片地震数据划分为基础,融入山地地震数据规则化和成像道集时差校正技术,获得高品质叠前五维地震成像数据。DX探区应用结果表明,炮道采样对称均匀的宽(全)方位、高覆盖、强耦合的高精度三维采集与OVT域全方位处理,基本能够实现山地探区深层页岩气地质目标的叠前方位偏移距地震信息的充分采集与保留,能够获得高品质、高精度、高信息丰度的地震成像数据,有效支撑深层页岩气构造保存评价、水平井轨迹设计与控制以及可压裂性预测等工作。

The beneficial exploration and development of deep shale gas requires seismic technology to implement the“sweet spot”area,in which it fractures easily for high production and has targeted the special demands for the imaging quality and information abundance of seismic data.First,high-quality imaging of faults,fault depressions,and low-order faults that are closely related to the structural preservation and evaluation of shale gas must be achieved.Second,high-quality,high-precision,and high information abundance pre-stack 5D seismic imaging data for the“sweet-spot”prediction of deep shale gas fracturing must be achieved.Driven by the key requirements of seismic data for the benefit exploration of deep shale gas in the Sichuan Basin,this study focused on seismic technology progress,including the design of geological target-oriented 3D geometry,processing of prestack full-azimuth information preservation,and its application in the DX target region of the Qijiang high-steep structural belt.Geological target-oriented 3D geometry utilizes multidimensional lighting and seismic data degradation processing to design an optimal observation system that meets the needs of geological target detection based on 3D surface and subsurface geological and seismic forward modeling.The prestack full-azimuth information preservation process integrates mountain seismic data regularization and image correction for time differences during the prestack migration processing to obtain prestack 5D seismic imaging data that fully retain offset and azimuth information based on the division of data with an offset vector tile(OVT).In the DX target area,3D high-precision seismic acquisition of wide azimuth(full azimuth),high fold,and strong coupling with symmetrical and uniform sampling of shot and receiving points and OVT full-azimuth processing were applied,which can realize the full acquisition and retention of prestack azimuth-offset seismic information of deep shale gas geological targets to provide seismic imaging data with high quality,accuracy,and information abundance for structural preservation evaluation,design,and control of horizontal well trajectory,and fracturing prediction of deep shale gas.