鄂尔多斯盆地志丹地区长2段低阻油层特征及油气地质意义

Characteristics of Chang 2 Low Resistivity Pay Zones and Petroleum Geological Significance in Zhidan Area,Ordos Basin

鄂尔多斯盆地志丹地区延长组长2段油层的电阻率普遍偏低,导致油层识别难度大,而长期作为非主力开发层系。围绕低阻油层存在的测井识别困难问题,通过对岩心、地层水、铸体薄片、黏土矿物、测井曲线、生产动态等资料的综合处理,分析地层水矿化度、微观孔隙结构、岩石矿物成分等典型特征对油层电阻率降低的影响,探讨研究区低阻油层勘探与开发的油气地质意义。结果表明:受三角洲平原亚相沉积背景控制,延长组长2段以中-细粒长石砂岩为主,在差异压实作用下储层孔隙类型多样;志丹地区地层水矿化度较高,并伴随微观孔隙结构复杂、黏土附加导电作用强等特征,流体与岩石构成的自由导电网络成为油层低阻的内在原因;长2段低阻油层是一类极具挖潜优势的隐蔽性油藏,将交会图法与邻近水层对比结果相结合,可以有效提高测井识别符合率。建议加强延长组长2段低阻油层的成因分析及测井识别研究,为延长油田老油区稳产挖潜提供理论依据。

The resistivity of the Chang 2 oil layer is generally low in the Yanchang Formation of the Zhidan area,Ordos Basin,making it difficult to identify the oil layers,and it has been viewed as a non-main development oil layer for a long time.Focusing on the difficulties of well-logging identification in low resistivity oil layers,the influence of typical characteristics of formation water salinity,microscopic pore structure,rock mineral composition on the reduction of reservoir resistivity through comprehensive processing of core,formation water,casting sheet,clay mineral,well-logging curves,production performance and other data was analyzed,and the petroleum geological significance of exploration and development in the study area was discussed.The results show that under the sedimentary environment of delta plain subfacies,Chang 2 oil layer is dominated by medium-fine-grained feldspar sandstone,and the pore structure is extremely complex due to the strong compaction.The high salinity of formation water in the Zhidan area,accompanied by complex microscopic pore structure and strong additional conductivity of clay mineral,which leads to the free conductive network formed by fluid and rock being the internal reason for the low resistivity of pay zones.Chang 2 low resistivity pay zones are kind of subtle oil layers with great potential for exploration and development,so combining the cross-plots with the comparison results of adjacent water layers can effectively improve the accuracy of well-logging identification.It is suggested that more attention to the analyses of low resistivity causes and the identification of the Chang 2 oil layer in the Yanchang Formation,so as to provide a theoretical basis for stabilizing production and tapping the potential of the old oil areas in the Yanchang oilfield.