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崎岖海底和海洋深水区速度的复杂性导致沉积层构造畸变、深度预测难度大,严重制约了深水区的油气勘探。利用测井速度、VSP速度对白云凹陷速度结构特征和影响因素进行了分析,结果表明,地层速度与海水深度不存在必然的联系,沉积环境的差别是陆架、陆坡深水区速度异常的根本原因,陆架坡折带是界定地层速度异常的关键。理论模型正演方法研究表明,叠前相干速度反演的精度高、可操作性强,是解决速度异常的有效方法。利用测井速度、叠前相干反演速度及地震叠加速度的优势互补,建立了白云凹陷时深转换速度场,较好地解决了深水区崎岖海底造成的构造畸变问题。利用建立的时深转换速度场转换得到B19井和B20井的深度,与实际钻井深度相比,T50反射层深度误差分别为6和7m,大幅提高了海洋深水区深度预测的精度。
The complexity of the velocity in the rugged seafloor and the ocean deepwater zone leads to structural deformation of the sedimentary layer, which makes it difficult to predict the depth and severely restricts the exploration for oil and gas in the deepwater area. The logging velocity and VSP velocity are used to analyze the velocity structure and influencing factors of Baiyun sag. The results show that there is no necessary relationship between the velocity and seawater depth. The difference of sedimentary environment is the fundamental reason of the velocity anomaly in deep shelf and continental slope. The slope break of the shelf is the key to define the abnormal formation velocity. Theoretical model forward method research shows that the prestack coherence velocity inversion accuracy and operability, is an effective method to solve the speed anomaly. Based on the complementarity of well logging speed, prestack coherence inversion velocity and seismic stacking velocity, the time-velocity field of Baiyun sag is set up to solve the tectonic deformation caused by the rugged seafloor in the deepwater area. The depth of B19 and B20 wells is obtained by using the established time-conversion velocity field. The depth errors of T50 reflectors are 6 and 7 m, respectively, compared with the actual drilling depth, which greatly improves the accuracy of depth prediction of deep-sea ocean areas.