陕北志丹油田樊川区长6~1低阻油层成因分析与识别方法

陕北地区延长组发育低(特)渗储层,除发育通常的高阻油层外,还极易形成低阻油层;因此,低阻油层的发现,极大拓宽了该区石油勘探和开发的领域。根据志丹油田樊川油区长61的石油地质特征,结合大量实验和生产数据资料的分析对比,对该区低阻油层的成因机理及宏观控制因素进行了分析。结果表明:长61储层的孔隙结构复杂导致束缚水饱和度增高,高地层水矿化度、高泥质含量及放射性砂岩的存在,是低阻油层得以形成的主要原因。通过大量实际试油和测井资料的对比可见,应用计算自然电位与自然电位曲线重叠法可以快速直观显示其含油性,声波时差-深电阻率的交会图与自然伽马-深电阻率交会图相结合可有效识别低阻油层。对区内85口探井进行了测井资料的二次解释,在长6发现了初次解释所遗漏的45个低阻油层,油层数由原来的117个增加到162个,净增27.8%。

Origin Analysis on Chang 61 Reservoir with Low Resistivity and Its Identificating Methods from Fanchuan Area, Zhidan Oil Field,in Northern Shaanxi, Ordos Basin

Low permeability or ultra-low permeability reservoirs are developed in the Yanchang Formation of northern Shanxi,in addition to the usual high impedance reservoir development,but also easy to form a low resistivity reservoir.Therefore,the discovery of low resistivity reservoirs has greatly widened the area of oil exploration and development fields.According to geologic characteristics of Chang 6-1 reservoir in the Yanchang formation of Fanchuan area,Zhidan oil field,combined with a large number of experimental and production data analysis and comparison,causes of low resistivity reservoirs in the area of macro-control mechanism and the factors were analyzed.We believe that the pore complex structure of Chang6-1 led to increased water saturation and high water salinity,high clay content and the presence of radioactive sandstone,which is the main reason for forming the low resistivity reservoir.Identification methods of low-resistivity reservoirs are presented by a large number of actual test comparison of oil and logging data.The results show that calculated spontaneous potential and spontaneous potential curve overlapping quickly and visually display oil layers,Crossplots of acoustic time-deep resistivity and gamma-deep resistivity can divide the oil and water layers.By the secondary log data interpretation of 85 exploration wells on the region,45 low resistivity oil layers those are omission in the initial interpretation are found in the Chang 6 reservoirs,and oil layer number changes from 117 to 162 with a net increase of 27.8%.