四川盆地VSP测井技术进展

Progress of VSP logging technology in Sichuan Basin

VSP技术在复杂构造和岩性油气田勘探开发领域发挥着越来越重要的作用,可为地面地震资料处理解释提供精确的时深转换及速度模型,改进地面资料成像处理的精度,实现井周地层高分辨率成像。为充分利用这些优越性,四川盆地开展了VSP测井可控震源激发、井中uDAS接收、井地联合采集与处理解释试验。结果显示:①相对于炸药震源而言,可控震源受地面激发条件影响相对小,炮间能量相对更加均衡,相对于零偏移距测井速度资料,其时深关系的求取也更加精确,且施工方面可控震源更加安全环保,可大大提高施工作业效率,降低勘探成本;②井中uDAS光纤传感器具有耐高温、高压、测量精度高、稳定性好、可测量深度大特点,能实现一次激发全井段接收,因此作业效率高,成本低,且时间采样和空间采样间隔更小,有利于识别几米甚至更薄的地层或储层,此外还可在超斜井、小口径等特殊油气井中使用;③井地联采则通过地面激发,地面与井中同时接收,利用井中VSP资料提取各种地球物理参数,驱动地面地震资料处理,井地联合处理剖面的频率通常可比常规处理剖面提高8~10 Hz,成像质量改善明显,绕射归位合理,断点清楚、干脆,可进一步提高地面地震资料对储层的描述能力。

VSP technology plays an increasingly important role in the exploration and development domains of complex structures and lithologic oil and gasfields.For example,it can provide accurate time-depth conversion and velocity model for surface seismic-data processing and interpretation,improve imaging processing accuracy of surface data,and achieve high-resolution imaging near borehole.In order to make full use of these advantages,some VSP logging vibroseis excitation,borehole uDAS receiving,well-ground joint acquisition,and processing interpretation tests were carried out in Sichuan Basin.Results show that(1)compared with explosive source,vibroseis is less influenced by ground excitation conditions and its energy among shots is more balanced.Compared with zero-offset logging velocity data,vibroseis can provide more accurate calculation of time-depth relationship and ensure environmentally friendly and safer construction,so as to greatly improve the operation efficiency and reduce the exploration cost;(2)borehole uDAS optical fiber sensor has some advantages of high temperature,pressure tolerance,and measurement accuracy,good stability,and great measurement depth,furthermore,it can realize full-hole reception in one shot,so its operation efficiency is high and the cost is low.In addition,its time and spatial sampling intervals are shorter,which is conducive to identifying the layers or reservoirs with several meters thick or even thinner.What's more,it can be used in special oil and gas wells,such as super deviated and slimhole wells;and(3)based on excitation on the ground and simultaneous reception on the ground and in the hole,the well-ground joint acquisition technology extracts various geophysical parameters through VSP data and drives the surface seismic-data processing.The frequency of well-ground joint processed profile is usually 8-10 Hz higher than that of conventionally processed profile,and the imaging quality is improved significantly with reasonable diffraction homing and clear and simple breakpoint,which may improve an ability of surface seismic data to describe reservoirs.