准噶尔盆地乌伦古坳陷WC1井高电阻率泥岩成因分析

Causes analysis for well WC 1 high-resistivity mudstone in Wulungu Depression,Junggar Basin

准噶尔盆地乌伦古坳陷的WC 1井在石炭系下统姜巴斯套组钻遇较长井段暗色岩层,录井定名为碳质泥岩,但该套地层在电测曲线上具有高电阻率特征,与上覆侏罗系中、下统和三叠系上统泥岩具有较大的差异,也与邻区白家海凸起CC 2井、车排子凸起P 66井钻遇的石炭系泥岩电性特征不同。岩心观察、岩屑样品薄片鉴定和地球化学分析表明,录井定名的碳质泥岩井段高电阻率特征主要成因是凝灰岩或凝灰质泥岩,因而将该井段定名为凝灰质泥岩井段更妥;其次要成因分别是火山灰含量高、岩石具脱玻化-硅化及绿泥石化现象,裂缝充填物为硅质或碳酸盐,且岩石演化程度高。地球化学分析认为,该井段岩屑样品分析的有机质含量并未达到碳质泥岩的级别,高电阻率现象与有机质无关,且生烃潜力有限。

Well WC 1of Wulungu Depression,Junggar Basin drilled with a longer interval black rock in Jiangbasitao formation of the lower Carboniferous system,which is named carbonaceous mudstone by mud logging.However,the set of the strata has high-resistivity feature on electric-log curve,great difference with mudstone overlying upper and lower series of Jurassic system and upper series of Triassic system,and the difference in electrical characteristics with Carboniferous mudstone drilled in adjacent well CC 2of Bajiahai bump and well P 66 of Chepaizi bump.Core observation,thin section identification of cutting samples and geochemical analysis showed that main cause of high-resistivity characteristics of the carbonaceous mudstone interval named by mud logging is the tuff and tuffaceous mudstone,therefore,the section was named more appropriately for tuffaceous mud stone interval;second causes are high volcanic ash content,rock with devitrification,silication and chloritization phenomena,fracture restraining mass is siliceous or carbonate,and the rock has high evolution degree.Geochemical analysis showed that the organic matter content analyzed from cutting samples of this set did not reach the level of carbonaceous mudstone,high-resistivity phenomenon is of no concern to organic matter,and hydrocarbon generation potential is limited.