磁测找油方法及其在陕北油气勘探中的应用

Studies of magnetic method for hydrocarbon reservoir and its application in northern Shaanxi,China

二十多年来,磁测找油方法作为非地震油气物探方法中的一种,在陕北油田进行了大量的试验及研究工作.为了系统归纳磁测找油方法研究进展及探讨其在陕北油气勘探中的应用效果,本文阐述了油气藏上方近地表微磁异常的形成机理以及磁性矿物的形成机制的研究进展,总结了由于地下油气藏的存在而引起的微磁异常的一般特征,分析了陕北吴堡-旦八地区已有油井及干井的分布特征与高磁剩余异常特征间的关系.结果表明,油气藏上方岩石中广泛存在的磁学-地球化学-矿物学异常与烃类微渗漏作用之间的相互关系基本可以成立,烃渗漏可以通过改变油气藏上方空间氧化还原条件等造成磁性变化从而在近地表产生磁异常变化,而这些磁异常在经过数据处理之后,可以提供微磁异常与油气藏之间高度的相关性.陕北吴堡-旦八地区高磁剩余异常与油井具有一定的相关性,高频、低幅度、高值异常带以及高值环带包围低值区块的环带异常与油气藏有较好的对应关系.虽然目前还不可能研究出一种可以完全消除或大部分压制地面上各种人文干扰产生磁场的方法技术,但是在开展高精度磁测工作时,尽量压制各种与油气藏无关的干扰磁异常,并且做好物性测定和样品分析,磁测找油方法仍不失为一种经济、快速、有效的方法.

During the last two decades, magnetic method for hydrocarbon reservoir, one of non-seismic geophysical techniques, was tested and studied a lot in northern Shaanxi. In order to generalize the progresses of magnetic method for hydrocarbon reservoir and discuss its application in northern Shaanxi, this paper describes the progresses of the formation mechanism of near-surface micro-magnetic anomalies and magnetic mineral above the reservoirs, summarizes the general characteristics of micro-magnetic anomalies caused by the subsurface reservoirs based on reading a lot of documents published, analyses the correlation between the distribution of oil and gas wells and dry wells and the features of residual anomalies of high-precision magnetic measurement in Wubao-Danba area in northern Shaanxi, discusses the effectiveness of application of magnetic method for hydrocarbon reservoir. The results show that the correlation between the widespread anomalies of magnetism, geochemistry and mineralogy in the rock above the reservoirs and hydrocarbon micro-seepage can be established. The study reveals that hydrocarbon leakage can change oxidizing reduction conditions of the space above the reservoirs to cause the changes of magnetic property of the minerals above the reservoirs, so as to producing magnetic anomalies near the surface. After these magnetic anomalies are processed, a high correlation between micro-magnetic anomalies and the reservoirs can be provided. Some relationships between residual anomalies of high-precision magnetic measurement and oil and gas wells exist in Wubao-Danba area in northern Shaanxi. The anomalous zones of high-frequency, low amplitude and high value and the annulus anomalies surrounded by low value block correspond preferably to the reservoirs in Wubao-Danba area. Meanwhile high-precision magnetic measurement is carried out, these magnetic anomalies unrelated to reservoirs are tried to suppress, and physical properties are measured and samples are analyzed. Although methods and techniques not yet are developed to completely eliminate or mostly suppress the magnetic field caused by human interference on the ground, the magnetic method for hydrocarbon reservoir is still an economical, fast and effective method.