海上大型气云发育区地震数据采集参数论证分析

根据渤海X油田气云发育区地质特征建立三维地震地质模型,模拟地震采集方式,考虑采集方向、排列长度、面元尺寸、覆盖次数以及激发频率等因素,建立了4种OBC采集观测系统。对4种观测系统利用三维声波方程分别进行正演模拟并对正演炮集数据进行克希霍夫叠前时间偏移成像。依据不同采集观测系统正演模拟得到的数据分析了气云下伏地层偏移成像剖面和时间切片,提出了5点采集建议:①沿气云短轴方向采集有利于改善下伏地层成像;②OBC束线采集方式下覆盖次数的变化主要影响气云下方埋藏较深地层的成像品质,对浅层地层的成像影响较小;③随着面元增大,地层成像质量变差,且地层埋深越大影响越严重;④低频震源激发是改善气云发育区下伏地层成像的关键;⑤加大排列长度可有效改善高陡地层的成像品质。上述采集建议在气云区实际采集中被采纳应用,新采集资料品质及成像质量相对老资料明显提高。

Demonstration analysis of seismic acquisition in a large-scale gas cloud area in the sea

Gas clouds are an important indicator of oil and gas migration.However,the presence of gas clouds poses a challenge for seismic data imaging.A variety of data processing techniques can be used to enhance the imaging quality of a gas cloud area and improving the seismic acquisition can solve the problem from the root.Firstly,based on the three-dimensional seismic-geological model of the gas cloud area in the X Oilfield in the Bohai Sea,seismic acquisition was simulated.Four ocean bottom cable(OBC)seismic observation systems were established,which differed in terms of values of parameters such as the direction and geometry of the acquisition,spread length,number of coverage units,bin size,and excitation frequency.Then forward modeling and pre-stack Kirchhoff time migration were implemented to investigate how the different observation systems performed in terms of gas cloud imaging.Five suggestions for improving the seismic acquisition were formulated:1)acquisition along the short axis of the gas cloud is beneficial for improving the imaging of the underlying strata;2)the number of coverage units affects the imaging quality of the deep layers(beneath the gas cloud)more than of the shallow ones(above the gas cloud);3)as the bin size increases,the imaging quality worsens;moreover,the deeper the stratum,the more significant the worsening;4)low-frequency source excitation is key to improving the imaging of the strata beneath the gas cloud;5)increasing the spread length can effectively improve the imaging quality of high-dip formations and faults.In summary,we demonstrated that the quality of seismic data and imaging can be improved by following the proposed suggestions.