海底电缆地震勘探中近正四面体法二次定位技术

在海底电缆地震勘探中,检波器的二次定位技术十分重要。本文详细阐述了三个炮点集中分布、两个炮点集中分布、三个炮点近于-条直线分布及三个炮点呈等边三角形分布并与检波点构成正四面体等四种炮点分布类型的初至距离、炮点坐标误差对检波点定位的影响,计算分析表明:前三种炮点分布类型在炮点坐标和初至距离存在微小误差时,对检波点定位精度的影响很大,其中初至距离误差的影响远大于炮点坐标误差;对于最后-种炮点分布类型,不论初至距离误差还是炮点坐标误差,对检波点定位精度的影响都很小。根据模型分析结果,文中提出了近正四面体定位技术,并建立了计算方法、选点原则和评价标准。近正四面体定位技术的核心思想是:按-定方法从众多的炮、检组合中优选出最接近正四面体组合进行计算,舍去偏离正四面体程度大的组合,将优选值再进行统计分析,能够有效地提高检波点定位精度。文中方法的实现简单,计算量小,具有实用性和创新性,模型分析和海上三维地震勘探二次定位实例均证明了该方法的合理性。

An approximate tetrahedron method for the seconda-ry positioning in OBC seismic survey

The secondary positioning of sensors is very important in the ocean bottom cable(OBC)seismic survey.In this paper,we discuss different shot point distributions,such as 3 shot point focus,2 shot point focus,3 shot points in line and 3 shot point triangle tetrahedral distributions.The computation and analysis results show that the first three distributions have a great influence on the sensor position accuracy even there are very small errors of the first arrival distance and the shot point coordinates.Moreover the first arrival distance error has much greater affects than the shot point coordinate errors.But with the tetrahedral distribution,both the first arrival distance error and the shot point coordinate errors has very small affects on the sensor position accuracy.Based on the model analysis results,the paper proposes a near tetrahedral secondary positioning method.Nearest tetrahedral combinations other than deviate combinations are chosen and calculated among many shot-receiver combinations on a large extent.Then the calculated results are statistically analyzed.Finally it is found that this approach can evidently increase sensor positioning accuracy.The method is not only simple but also computational efficient.Both model and offshore 3D examples show the validity and rationality of the method.