涪陵焦石坝三维工区高精度速度建场方法

页岩气层构造形态描述精度直接关系到水平井轨迹设计的准确性和可靠性。利用时间域地震资料描述深度域地下构造形态,关键是在工区建立高精度平均速度场。针对涪陵焦石坝三维工区地表及地下地震地质特点,提出并实现了基于表层模型的叠加速度CMP浮动基准面时间域到深度域的转换、模型迭代层速度计算、基于层位约束的两步法层速度误差趋势面构建、平均速度场随钻实时更新等方法,形成了一套适用于山地起伏地表的高精度三维速度建场技术。该套技术应用于焦石坝页岩气产建区,提高了变速成图精度、水平井井轨迹设计准确率、优质页岩气层钻遇率以及钻井效率,降低了钻井成本。

The structural description of shale gas reservoirs is relevant to the design precision of horizontal well trajectory.Building a high-precision velocity field is key for describing the subsurface structure in the depth domain using seismic data.Based on the characteristics of the surface and underground seismic geology in the research area,a set of high-precision 3D velocity field building techniques was developed.The technique includes several process steps,namely,the velocity field transition from the time domain to the depth domain,interval velocity calculation based on layer model iteration,two-step interval velocity error trend surface construction based on horizon constraint,and average velocity field updating in real time while drilling.The results of application in the Jiaoshiba 3D seismic survey area of the Fuling shale gas field showed that the proposed technique could help improve the accuracy of variable velocity mapping and the design of horizontal well trajectory,improve the rate of drilling encountering high-quality shale gas formations,and improve drilling efficiency and reduce drilling costs.