【摘要】 发育了一系列岩性圈闭的琼东南盆地坡折带是天然气勘探的重点目标和领域,但在该坡折带上,当沿斜井轨迹的水深变化很大时,常规计算时深关系的方法往往会失效,致使时深关系求取困难。为此,从理论上剖析了该坡折带上常规VSP测井和声波测井计算的时深关系与准确时深关系之间存在差异的原因。结果表明:常规声波测井和VSP测井是沿井轨迹方向计算时间和深度值的,只考虑了井口位置上的水深影响,而在斜井变水深的条件下,求取时深关系则需要计算井轨迹上每个点的垂向深度及其所对应的传播时间且不同位置对应着不同的水深值。在理论研究的基础上,采用变水深斜井VSP速度建模方法,开展了射线追踪正演模拟;通过分析VSP正演记录初至时间和实测记录初至时间的相关关系,进行速度模型迭代更新,建立了井附近地层的速度模型,从而得到坡折带上沿斜井轨迹水深变化条件下的时深关系。结论认为,与常规基于标志层方法计算的时深关系相比,所建立的变水深斜井VSP速度建模方法不受地面地震资料品质的限制,保证了井轨迹上每个点时深关系的准确性且精度更高。更多还原

【Abstract】 The slope-break belts of the Qiongdongnan Basin,in which a series of lithologic traps are developed,are the main exploration targets.With a varying underwater depth ranging from 200 mto 2 000 min the slope-break belts,it is very hard to get the true T-D relationship for a deviated well because those conventional methods don’t work well.Therefore,a theoretical analysis was performed on why the exact T-D relationship is different from that obtained from VSP and sonic logging.In the conventional VSP and sonic logging,the time and depth values were calculated along the well trajectory,which refers to the water depth from the wellhead only.But under the condition of varying water depth of a deviated well,the T-D relationship should be calculated with the vertical depth and the corresponding time at each point along the well trajectory taken into consideration.Based on a theoretical research,we introduced the VSP velocity modeling with varying water depth along the well trajectory.Following the ray-tracing forward modeling,the arrival time of VSP synthetic data was picked,and was compared with the VSP measured data.Then the initial velocity model is updated with iteration,and an accurate velocity model was established finally for the strata near a deviated well.In this way,it became easy to get the accurate T-D relationship of the deviated well with different water depths along the well trajectory now.This method is independent from surface seismic data quality,and the T-D relationship followed is more accurate than that with conventional methods based on the marker beds.更多还原