三维VSP观测系统设计研究

 三维VSP观测系统设计取决于地面炮数、井下可利用检波器数目、井源距、检波点深度、炮点分布和检波点分布等方面，设计合理的观测系统能够改善井孔附近地层的三维成像效果。通常可以通过覆盖次数和井源距等面元属性参数来衡量三维VSP观测系统设计的合理性。本文研究了井源距和检波点深度、炮点和检波点的分布对纵波和转换波的观测范围、覆盖次数的影响，通过计算与分析，得出以下认识：①检波点深度越小、井源距越大，则观测面积越大；②PS波观测面积小于PP波观测面积；③在检波器个数和炮点分布固定的情况下，适当增加检波点间距有利于覆盖次数均匀；④在炮点呈环形分布或束状分布且炮点间距与炮线间距相当时覆盖次数较为均匀，PP波、PS波覆盖次数的均匀程度基本相当。

Study on design of 3-D VSP geometry

The design of 3-D VSP geometry depends on number of shots on surface, number of geophones available in well, offset, depth of receiver point, distribution of shots and receiver points. Designing reasonable geometry can improve 3-D imaging results around borehole. Generally, we can evaluate the reasonability of 3-D VSP geometry design by such bin attributes as folds and offsets. The paper studied the influences of offsets,folds and distribution of shots and receiver points on surveying scope and folds of P-wave and converted wave, and got following knowledge by computation and analysis: (1)the shallower the depth of receiver points and the larger the off sets, the larger the surveyed area; (2)the surveyed area of PS-wave is less than that of PP-wave; (3)in a condition fixing number of receivers and distribution of shot points, increasing adequately the interval of receiver points is advantageous to the uniform folds; (4)in a condition of ring-like or bunch-like distribution of shot points, the folds are uniform and uniformity of PP-wave and PS-wave is basically equivalent when the shot-point spacing is equivalent to shot line interval.