地表放射性异常与地下油气藏关系研究

为探索地表放射性异常与地下油气藏的关系，在４种类型的９个油气藏上收集了３１０口井的放射性测井数据，同时在５个油气藏上补充进行了地面放射性测量工作。测量结果表明，放射性异常从油层到地表具有延续性；在同一油层上方异常随测点与油层距离加大而减弱；复合式油气藏各油层异常独立存在；不同类型油藏异常总体形态相似，异常幅值与油藏圈闭条件有关；地表放射性异常形态和幅度受油藏埋深影响不大，但与油藏规模有一定关系。这些为油气物质垂直运移及放射性异常深部形成机制提供了直接证据。在此基础上，综合前人研究成果，提出了油田放射性物质来源主要是生油岩的观点和油气盆地内流体微运移循环的设想，建立了放射性异常综合成因模式，即：放射性物质伴随油气运移，在重力分异作用下，聚集在油藏周围水中；由于盖层对油水的排替压力不同，形成有利于水穿过盖层的条件；放射性物质与水一起在流体微运移循环作用下，沿微裂隙和孔隙运移到地表，形成油田边界高值放射性异常；油藏顶部地表放射性值的高低受氧化还原条件、潜水面深度和其他地表因素控制。

STUDY ON CORRELATION BETWEEN SURFACE RADIOACTIVE ANOMALY AND UNDERGROUND OIL RESERVOIR

n order to interprete relations between the surface radioactive anomaly and the underground oil reservoir, the radioactive log data were collected from 310 wells in 9 oil reservoirs from 4 types of trap,and supplementary surface radioactive measurements were carried out in 5 oil reservoirs. The data show that the anomalies are continuous from an underground oil reservoir to the surfacel that the radioactive anomaly in the same reservoir may reduce as the distance between the measurement point and the oil reservoir increasesl that in the oil field with multiple reservoir or multiple layers,the high value anomalies on the boundaries of each layer are individual; and that the morphological features of the anomalies of different types of reservoirs are quite similar,but their anomalous values are related to their oil trap conditions.All of these exhibit the direct evidence for the vertical migration of radioactive materials in the ground. On the basis of analyzing the radioactive lOg data, the authors point out that the main material source of radioactive anomaly in the oil field is the source rock in the oil basin and that the pressures of overlying strata and static water, the geothermal and the gas buoyancy causemicro-cycle of fluid transportation in the oil basin. A comprehensive model of radioactiveanomaly is set up. Radioactive materials move and accumulate in the water around the oil reservoir under the effect of oil and gas migration and gravitational differentiation. As a result of difference of the blead-off pressure between oil and water, it is easy for radioactive elements to penetrate through the cover and move to the surface along the micro-fractures and pores with water.The values measured on the surface of central reservoir depend on the factors, such asreduction-oxidation condition and ground water level,etc.