砂岩型铀矿三维地震勘探采集关键技术及效果

Key acquisition technology of 3D seismic exploration for sandstone-type uranium deposits and its applied results

砂岩型铀矿凭借大矿量、低成本、开采污染小等优势,现已成为中国铀资源量增长最快和占有铀资源量最大的铀矿床类型.三维地震勘探是间接探查深部砂岩型铀矿成矿环境最有效的技术手段之一,然而在中国砂岩型铀矿勘查区:(1)目标层埋藏深度浅,一般小于1000 m,局部小于200 m,浅层资料覆盖次数较低,且易受表层采集噪声干扰,信噪比低,成像质量差;(2)目标含矿砂体常赋存于"泥砂泥"、"煤砂泥"等互层结构中,一方面目标砂体的厚度较小(几米至几十米不等),另一方面目标砂体与围岩的弹性差异小,因此导致目标体的反射信息较弱,准确分辨的难度较大.以内蒙古齐哈日格图凹陷砂岩铀矿区为试验区,开展了具有针对性的采集关键技术试验研究,建立了一套基于"小面元、中等覆盖次数、宽方位"三维观测系统设计方法,"少震动台次、宽频扫描"可控震源激发方法,"点式组合、宽频带接收"检波器接收技术,以及"多次锤击叠加相遇小折射法+高密度电法"快速表层调查方法的砂岩型铀矿三维地震数据采集技术.通过原始资料频谱、处理效果、解释反演结果的对比分析可知,该技术采集的原始资料品质较佳,是今后砂岩型铀矿三维地震勘探工作的重要参考.

Sandstone-type uranium mine has become the main type of uranium deposits with the fastest growth of uranium resources and the largest uranium resources in China due to its large reserves, low cost, and low pollution. Three-dimensional seismic exploration is one of the most effective techniques for detecting indirectly the mineralization environment for deep sandstone-type uranium. However, there are several difficulties in the seismic exploration of sandstone-type uranium deposits:(1)the buried depth of the target layer of uranium deposit is shallow, generally less than 1000 m, and the local area is less than 200 m, which causes the number of shallow data coverage is low, moreover, the shallow seismic data is easy to be interfered by the surface noise when data acquisition, the signal-to-noise ratio of the shallow data is low, and the imaging quality is poor.(2)the target ore-bearing sand bodies often occur in the interbedded structures such as "mud sand mud", "coal sand mud", on the one hand, the thickness of the target sand body is relatively small(ranging from several meters to tens of meters), on the other hand, the acoustic impedance difference between the target sand body and the surrounding rock is small, as a result, the strength of seismic signal of the target layer is weak and it is difficult to distinguish accurately. This paper carried out targeted research and development of key technologies for data acquisition, which is the first research project of three-dimensional seismic exploration technology used for sandstone-type uranium deposits in China, then a set of three-dimensional seismic data acquisition technique for sandstone-type uranium mine was established, include the observing system designing method base on the "small bin, appropriate folds, wide azimuth", exciting method of vibroseis for small excitation numbers and broadband scanning, signal receiving technique for the point combination of geophones, which are buried in the dug holes near the surface, broadband receiving, and a series of rapid method for surveying the shallow velocity structure by a combination of multiple hammering meeting refraction method and high density electrical method. Through the researching for the original data spectrum, processed results and interpretation of the inversion results, it is considered that the quality of the original data obtained by the acquisition technology of sandstone-type uranium in this paper is good, which is an important reference for the future seismic exploration of sandstone-type uranium deposits.