乐东—陵水坡折带速度分析及时深转换方法

Velocity analysis and time-depth conversion study of Ledong-Lingshui slope-break belt

南海西部海域琼东南盆地乐东—陵水坡折带的地层倾角变化大,沉积相复杂,并存在异常压力带,使地层速度的分析也变得复杂,而速度是时深转换和压力预测的关键,所以理清坡折带速度的变化规律及影响速度异常变化的主控因素是该区研究的重点。为此,首先通过分析地震资料和井上声波资料,总结了乐东—陵水坡折带的速度分布规律,发现在乐东—陵水凹陷内陵水组到黄流组之间存在低速反转带,并由深层到浅层、坡下到坡上方向,速度反转的强度和范围逐渐减小;然后,结合地质和压力等资料,分析影响坡折带速度变化的因素主要有水深、地层倾角、压力和异常岩性体等;最后,将坡折带速度体应用于三个目标砂体的时深转换,对比不同井校方案下的时深关系及时间、速度和深度等值线图,对于不同目标的设计井采取不同的井校方案,得到最合理的时深关系。

In Ledong-Lingshui slope-break belt of Qiongdongnan Basin in western South China Sea,the stratigraphic dip changes a lot, the sedimentary facies is complex and there is abnormal high pressure zone. All these factors make the velocity analysis complicated while velocity is the key to convert time to depth and to predict pressure.So it is important to ravel out the velocity change rules and in-fluence factors in the slope-break belt.For this purpose,the authors analyzed the seismic velocity volume and well sonic data to get the velocity distribution regularity and found that it corresponds to the ordinary distribution rules except for an abnormal low velocity zone spread out from Lingshui to Huangliu formation,which fades away from shallow layer to the depth and from downslope to upslope. In combination with the geology and pressure information,it is found that the main factors influencing the velocity change rules include depth of water,formation dip, pressure, abnormal lithologic body et al. Based on above understanding, the authors applied the slope-break belt velocity volume to three sand bodies ＆#39; time-depth conversion. Different calibration cases are comparatively studied with the time-depth relationship and time/velocity/depth contour map.At last the most reasonable calibration methods were chosen for different sand proposal wells.