煤层对砂岩地震反射特征的影响及其地震岩性学意义—以鄂尔多斯盆地山2段为例

Based on the earlier research for Permian Shan 2 member in Ordos Basin, Digital Outcrop model ( DOM ) of coal-bearing series will be established using collected point cloud data by Terrestrial scanning radar and measured outcrops in Shanxi Kouzhen. Using a combination of P-wave velocity and density data measured in laboratory, and drilling geological stratification , density and acoustic log data in Gaojiahe 3D seismic survey, the 0 and 90 phase DOM of two-dimensional synthetic seismic profile and three-dimensional synthetic seismic data will be obtained by using numerical simulation and 3D simulation technology, respectively. The effect of coal seams on seismic reflection characteristics of sandstone will be analyzed, which deepens the understanding of the seismic reflection characteristics; and the significances of seismic event polarity and the controlling factors which seismic reflection polarity have lithological significance can be reserached; finally, the problem of lower accuracy for prediction of sandstones and depositional systems in coal-bearing strata by using seismic amplitude information is solved through this research. As a result, the stratigraphical characteristics of seismic events can be deeply understood and then the quantitative relationship between the thin sandstone ( < λ /4 ) thickness and seismic reflection amplitude in coal-bearing strata can be established, thus the improvement of theory and method of seismic lithology can be achieved; and the prediction accuracy of sandstone and depositional systems can be improved through this study, which will increase the exploration success ratio of tight sandstone gas reservoir in coal-bearing strata.

研究的方法及技术是：基于对鄂尔多斯盆地二叠系山2段前期研究的基础上，利用陆地扫描激光雷达采集的陕西口镇野外露头点云数据和实测的露头剖面资料，建立含煤岩系数字化露头模型（DOM）。结合实验室测定的岩石纵波速度、密度资料及高家河三维地震探区钻井地质分层、声波时差、密度资料，采用数值模拟和三维仿真技术，分别形成0 和90 相位DOM二维合成地震剖面和三维合成地震数据体。解决的关键问题是：分析煤层对砂岩地震反射特征的影响，深化对地震反射特征的认识；研究地震反射同相轴极性的意义以及什么条件下地震反射同相轴极性具有岩性意义；解决利用地震振幅信息预测含煤岩系中砂岩及沉积体系精度较低的难题。研究目的是：深刻认识地震反射同相轴的地层学性质；建立含煤岩系中薄层砂岩（<λ/4）厚度与地震反射振幅之间的定量关系，完善地震岩性学理论和方法；提高地震预测砂岩及沉积体系的精度，增加含煤岩系中致密砂岩气藏勘探成功率。

本项目通过对鄂尔多斯盆地露头地层的观察，对目的层进行了高分辨层序地层研究，在目的层中划分出以上升半旋回为主的低可容空间、以上升半旋回为主的中等-高可容空间、以下降板旋回为主及对称旋回4类短期旋回叠置类型。将目的层中所发育的短期旋回层序结构可划分为2种基本类型和5种亚类型。通过对研究区露头剖面、钻井岩心、录井资料和测井曲线的详细观测、描述和对比分析，依据岩石组合、沉积组构、剖面结构和演化序列，结合区域地质背景资料对目的层进行了沉积体系研究，识别出分别发育障壁岛海岸、浅水三角洲和曲流河三角洲-湖泊等沉积相类型。根据声波和密度测井资料，利用褶积模型，得到了不同子波主频的合成地震记录,通过提取合成地震记录的砂岩顶、底界面或砂岩中心振幅，模拟了0°和90°相位子波情况下煤层对砂岩地震反射特征的影响。研究表明，煤层的厚度、位置及与砂岩的距离对砂岩地震反射调谐频率、调谐振幅、反射强度及极性都会产生影响。煤层可以使砂岩地震反射同相轴极性发生反转，甚至导致薄层砂岩厚度不可预测。特别是当煤层厚度不稳定时及煤层距砂岩的距离发生变化时，砂岩顶、底面或中心地震反射振幅不能反映薄层砂岩的厚度。对于不同厚度、位置的煤层，应采用不同位置的振幅地层切片来预测薄砂岩的厚度。本项目对实际的高家河三维地震资料进行了针对性处理，极大的降低了煤层干涉作用。建立高频等时地层格架，形成相对地质时间数据体。利用振幅信息，多学科结合，建立含煤岩系地震沉积相模式。