黄土塬区模型约束折射静校正技术应用研究

Application of the technology of model constraint refraction statics on loess area

鄂尔多斯盆地东缘黄土塬区地形起伏剧烈,低降速层厚度和速度横向变化大,表层结构复杂,折射波静校正表层模型建模困难,静校正问题突出.本文通过黄土塬区表层结构规律分析,提出了一种基于初至走时层析求取近地表速度、以等速度界面近似高速顶界面的表层模型约束建模方法;在基准面静校正概念的基础上,对比分析了基岩顶界面、层析速度收敛面等不同折射面解释方案对静校正量、标志层反射时间及平均速度的影响,结合实际钻井资料证实了在黄土塬区以基岩顶界面作为折射面能够获得正确的静校正量、标志层反射时间与平均速度.

The near surface structure in the loess area eastern of Ordos Basin is quite complex with the irregular topography and the rapid changing of both the thickness and velocity of the low velocity layer horizontally. Field statics correction is an outstanding problem of seismic exploration and it＇s usually hard to acquire optimum near surface model parameters for calculating refraction field statics in the loess area. According to the characteristics of the near surface structure in the loess area,the velocity isoline corresponding to the top of bedrock determined on the near surface velocity section,which is derived from first break time tomography,can be treated as a good approximation to the real refractor. Thus this approximate refractor can be taken as the constraining information while setting up the near surface refraction model. Since the parameter of model base has significant influences on the datum statics, both the reflection time and average velocity of key marker bed,two different refractor interpretation schemes including the top of bedrock and surface of velocity convergence in depth direction are tested and analyzed. Based on the concepts of datum statics and with the available well data,the scheme that taken the top of bedrock as the model base can obtain accurate datum statics,and both reflection time and average velocity for key marker bed.