黄土厚度变化较大地区煤田三维地震勘探时深转换方法的探讨

Probe into Coalfield 3D Seismic Prospecting Time-depth Conversion in Variable Loess Thickness Areas

时深转换是煤田三维地震资料解释中非常关键的一步,时深转换方法的选取直接关系到地质成果的准确程度。针对山西某勘探区黄土覆盖厚度大且变化剧烈的实际情况,在比较大平均速度和分层速度两种时深转换方法的适应性和误差特点的基础上,优选分层速度计算方法作为本区时深转换方法。具体步骤为:根据地层沉积相和地质构造特点,结合由速度谱数据库和声波测井速度数据库确定的岩性分布规律,以单斜为基本单元进行区块划分;计算出各区块的新生界、煤系地层的厚度和速度后,从而求出较为准确的煤层埋深。实例表明,采用分区块、分层计算的煤层底板深度不仅准确程度高,而且还能克服由大平均速度时深转换方法造成的煤层假构造现象。

The time-depth conversion is a very crucial step in the coalfield three-dimensional seismic data interpretation, and the selection of method is directly related to the accuracy of geological results. In this paper, we studied an exploration area in Shanxi which is covered by loess with variable thickness, based on the comparison of adaptability and error characteristics of average velocity and interval velocity two time-depth conversion methods, the interval velocity method is selected. Concrete steps are： according to sedimentary facies of strata and geological structure, combined with lithological distribution pattern determined by velocity spectrum and acoustic velocity logging data, to take monoeline as basic unit in block division; after estimation of Cenozoic and coal measures strata thicknesses and velocities, evaluated rather correct coal seam buried depths. Practices have demonstrated that, coal floor depths estimated through block partitioning and stratifying not only have higher accuracy, but also can eliminate coal seam structural phantasms caused by average velocity time-depth conversion method.