论文详情
零偏VSP以水平地层为假设条件,当地层倾斜时,零偏VSP时深关系精度和走廊叠加记录精度出现误差,更严重的是,走廊叠加记录上观测井段之下地层的上行反射波成像位置错误,需进行倾角时差校正处理。针对复杂高陡构造零偏VSP资料处理,提出了空变倾角时差校正的基本概念和方法,利用零偏VSP上、下行波场计算反射界面倾角,建立二维层速度初始模型,通过射线追踪修正速度模型,使倾角空间变化的高陡构造地层的VSP上行反射波场得到充分拉平,不仅提高了零偏VSP走廊叠加记录的精度,而且观测井段之下地层的上行反射也得到有效拉平并能精确成像,从而实现观测井段之下地层深度的精确预测和波组特征预测,时深关系也校正到地震波自地面震源到井下检波器的铅直传播时间,有效解决了复杂高陡构造的零偏VSP时深关系、层位标定和钻前地层预测等问题,实际资料处理效果验证了方法的有效性。
Zero-offset VSP is based on the assumption of horizontal strata.For inclined layer,the time-depth relationship and seismic corridor stack of zero-offset VSP is not accurate,and more seriously,the imaging position on corridor stack record under observation well section is incorrect,so we need to conduct DMO correction.For complex high-steep structure,we propose a modified method of space varying DMO correction for zero-offset VSP data.Firstly,the down-going and up-going waves are used to calculate dip angle of reflection interface,an initial 2D interval velocity model is established.Then,by tracing down-going and up-going wave’s ray path with ray tracing algorithm,the above velocity model is amended,which can make the up-going waves of zero-offset VSP from complex high-steep structure come to flat.It not only enhances the accuracy of corridor stack record,but makes up-going wave correctly imaging under observation well section.Therefore,the accurate prediction of formation depth and seismic reflections characteristics are achieved.Time-depth relationship is also corrected to direct path wave travel time in vertical depth,which effectively resolves problems such as time-depth relationship,seismic horizon calibration and pre-drilling prediction in complex high-steep structure.The actual data processing shows the effectiveness of the method.
国家科技重大专项“塔里木前陆盆地油气富集规律、勘探技术与区带和目标优选”(2011ZX05003-04)资助。