宁夏固原炭山地区中侏罗统延安组油页岩特征及其沉积环境

Oil Shale Characteristics and Sedimentary Environment of Yan’an Formation in Middle Jurassic in Tanshan Area,Guyuan,Ningxia

宁夏固原炭山地区存在大量与煤伴生的油页岩资源,油页岩主要赋存于中侏罗统延安组中下部各含煤层系中。本文采集钻孔所获延安组油页岩岩心样品,通过低温干馏、主量元素测定以及钻井录井等方法对炭山地区油页岩特征进行了研究,明确了油页岩测井识别依据,恢复了油页岩沉积环境。研究表明:炭山地区油页岩主要以黑色、灰黑色、深灰色为主,质地较轻,密度小,硬度小,断口参差状、贝壳状,具油脂光泽、沥青光泽,块状层理发育;油页岩含油率为3.60%~9.00%,灰分质量分数为42.50%~79.05%,全硫质量分数为0.07%~1.37%,发热量为11.01kJ/g(平均值),属中品质、硅质灰分、低硫且与煤伴生的油页岩;油页岩中w(SiO2)变化较大,为53.89%~65.55%,w(Al2O3)为17.45%~23.29%,w(K2O)明显高于w(Na2O),w(Fe2O3+MgO)为12.75%~21.98%,表明油页岩中含有较多的含钾矿物和镁铁成分;另外,Al2O3/(CaO+Na2O)值为3.09~21.12,揭示油页岩稳定组分含量较高。炭山地区油页岩测井曲线特征明显区别于煤层和泥岩,油页岩长距伽马、声波时差和密度介于煤层与泥岩之间,而电阻率明显低于煤层和泥岩。炭山地区油页岩化学蚀变指数为74.87~84.35,Sr/Ba值为0.33~0.83,平均为0.61,Th/U值为1.00~3.50,表明本地区油页岩沉积环境为温暖、温润的缺氧、贫氧的陆相淡水湖泊环境和沼泽环境。

There are abundant oil shale resources accompanied with coal in Tanshan area.Oil shale are mainly existed in coal-bearing strata of the middle and lower part of Yan’an Formation in Middle Jurassic.Based on the oil shale samples of Yan’an Formation obtained from boreholes,the characteristics and sedimentary environments were studied,and the identification basis of oil shale logging was defined in Tanshan area by low-temperature dry distillation,main element measurement,and drilling logging.The research shows that the oil shale in Tanshan area is mainly black,grayish black and dark gray,with light texture,low density,and low hardness.The oil shale has the characteristics of staggered,shell-like fracture,grease,asphalt luster,and block layer development.The oil-bearing ratio is 3.60%-9.00%,the ash is 42.50%-79.05%,the total sulfur is 0.07%-1.37%,and the calorific value is 11.01kJ/g(average value),which belongs to medium quality because it is siliceous ash,low sulfur,and associated with coal.The content of SiO2in oil shale varies greatly from 53.89%to 65.55%,Al2O3is 17.45%-23.29%,K2O is significantly higher than Na2O,and Fe2O3+MgO value is 12.75%-21.98%,containing many potassium-bearing minerals and magnesium iron components.The Al2O3/(CaO+Na2O)value is 3.09-21.12,which reveals that the stable components in oil shale are high.The logging curves characteristics of oil shale are obviously different from the coal seams and mudstones.The data of gamma,sonic and density of oil shale are between the coal seam and the mudstone,and the resistivity is significantly lower than the coal seam and mudstone.The chemical alteration index of oil shale is 74.87-84.35,Sr/Ba value is 0.33-0.83with average of 0.61,and Th/U value is 1.00-3.50,indicating that the oil shale sedimentary environment in Tanshan area was a warm,anoxic,and oxygen-poor terrestrial freshwater lake environment.