南堡凹陷下古生界表生岩溶特征及识别

Carbonate supergene karstification features and identification of the lower Paleozoic in Nanpu sag

综合野外、岩心、地震、钻、测井和分析化验资料,总结南堡凹陷下古生界碳酸盐岩表生岩溶特征,分析不同类型的岩溶识别标志,确立识别方案并进行实例应用.结果表明:南堡凹陷下古生界表生岩溶可划分为晚印支—早燕山期和喜马拉雅期;表生溶洞多呈倒置漏斗形,内部多形成岩溶塌陷体或被各种黏土充填;表生岩溶带在地震剖面上主要表现为同相轴不连续—弱振幅的杂乱反射特征;泥浆漏失段发育在距不整合面30m范围内;测井曲线上为高伽马—高声波—高井径—低密度—低电阻率—暗色成像斑块的组合特征;表生溶孔在阴极射线下显示明亮的橙色发光条带,碳、氧同位素值呈明显负向偏移的特点.以钻井响应和测井组合特征为主要识别标志,岩石学特征和地震反射标志为次要识别标志,地球化学特征为辅助识别标志,在NP280井中识别3个表生岩溶带.该方法可以有效地针对表生岩溶储层进行精细识别,为相似地区的碳酸盐岩勘探提供理论依据.

Combined with the data of field observation,core,seismic profiles,well drilling and logging,and geochemistry,we summarized the characteristics of supergene karst of lower Paleozoic carbonate rocks in the Nanpu sag,analyzed different types of identification marks of karst,established the identification methods and used these methods in a case study.The results suggest that the supergene karst of lower Paleozoic in the Nanpu sag can be divided into two periods:The late Indosinian to early Yanshanian period and the Himalayan period.Most of the supergene karst cave show inverted funnel in shape,with karst collapse body or different types of clay filled in them.In the seismic profiles,the supergene karst belts present disorder reflection with discontinuous and weak amplitude events.The leak part of drilling mud are all developed within the scope of 30 mfrom the unconformity surface.In the drilling logs,the supergene karst belts show the combined features of high natural gamma ray-high acoustic-high borehole diameter-low density-low resistivity-dark image patches.Under the cathode ray,the supergene pores show bright orange belts,and the carbon and oxygen isotopes trend to negative direction.Using the drilling data and logging data as the major identification marks,with the lithological and seismic reflection as the secondary identification marks and the geochemical characterisitcs as the assistant marks,we recognize three supergene karst belts in the well NP280.These methods can be efficiently used in identifying supergene karst reservoir,and provide theoretical proofs in the exploration of carbonate rocks in the similar area.