鄂尔多斯盆地东仁沟地区长2_1油层低电阻率成因与测井识别

Origin Analysis and Logging Recognition of Chang 2_1 Low Resistivity Reservoir in Dongrengou Area of Ordos Basin

低电阻率油层表现为电阻率接近甚至低于邻近水层,使得油层在电性特征上难以与水层进行区分,给测井解释带来较大困难。鄂尔多斯盆地东仁沟地区三叠系长21油层孔隙结构复杂,孔隙度与渗透率的相关性较差,为中孔、中渗到低孔、低渗储集层。利用测井、试油、水性分析、扫描电镜、岩心分析等资料,对长21油层的低电阻率特征的成因进行研究。分析了束缚水含量、含水饱和度、地层水矿化度及黏土矿物阳离子附加导电性等4种因素对长21油层形成低电阻率油层的影响,其中高束缚水饱和度、高含水饱和度和高地层水矿化度是长21油层低电阻率特征形成的主要原因。利用重叠图和交会图技术对研究区内低电阻率油层进行了分步骤的识别,分析结果证明两种方法配合使用准确度较高,与油层的试油结果匹配度好。

The reservoir with low resistivity presented that the resistivity was close to or less than that of water layer,it caused difficulty for distinguishing oil layer from water layer in electrical characteristics,and induced problems for logging evaluation.The pore structure was complex in Triassic Chang 21reservoir in Dongrengou Area of Ordos Basin,the correlation between permeability and porosity was poor,it was the reservoir with middle porosity and permeability to low permeability and low porosity.Analysis and research on the causes of low resistivity characteristics of Chang21reservoir were studied by using data of well logging oil testing,water property analysis,scanning electron microscope and core analysis.The influences of four factors,such as content of irreducible water saturation,water saturation,the salinity of formation water,cationic electrical conductivity of clay mineral were analyzed on resistivity of Chang 21reservoir, of which the high irreducible water saturation,high water saturation and high salinity of formation water were main factors causing resistivity feature.The low resistivity reservoirs in the studied area are identified step by step by using overlays and crossplot technologies,the results prove that the two methods are used integrally with a high accuracy,it matches well with the results of oil testing.