鄂尔多斯盆地西缘奥陶系乌拉力克组页岩气勘探潜力——以忠平1井为例

Shale gas exploration potential of Ordovician Wulalike Formation in the western margin of Ordos Basin:Case study of Well Zhongping 1

忠平1井的勘探突破揭示了中国北方海相页岩气在富集条件方面与南方海相页岩气有较大差异。通过最新钻井资料及野外露头剖面对鄂尔多斯盆地西缘奥陶系乌拉力克组低TOC含量"新型"海相页岩气富集地质条件及勘探潜力,包括泥页岩的矿物组分、孔隙特征、有机地球化学特征、含气性等参数进行了研究,结果表明:(1)乌拉力克组泥页岩矿物组分以长英质矿物为主,其次为碳酸盐矿物和黏土矿物,黏土矿物以伊利石和伊/蒙间层为主,其次为绿泥石、高岭石。(2)乌拉力克组孔隙度低(基本小于2.0%),以粒内孔、微裂缝为主要储集空间,有机质孔不发育;孔隙以中孔发育为主,孔隙发育受控于岩性。(3)泥页岩有机质类型属于Ⅰ—Ⅱ1型,其中以Ⅰ型(即腐泥型)干酪根为主;TOC含量主要介于0.1%~3.71%之间,平均为0.49%;有机质镜质体反射率(RO)分布于0.8%~2.5%之间,大部分处于高—过成熟阶段,不同地区有一定差异性。(4)乌拉力克组泥页岩现场解吸气含量分布在0.07~0.63 m^(3)/t之间,平均为0.3 m^(3)/t,运用USBM法对损失气量进行恢复,得到的损失气量为0.43~1.83 m^(3)/t,平均为1.09 m^(3)/t,地下总含气量介于0.76~2.46 m^(3)/t之间,平均为1.65 m^(3)/t,反映乌拉力克组泥页岩含气性较好,揭示中国北方海相泥页岩具有较好的页岩气勘探潜力。

The exploration breakthrough of Well Zhongping 1 reveals that the marine shale gas in northern China is quite different from that in southern China in terms of accumulation conditions.Based on the latest drilling data and field outcrops,the geological conditions and exploration potential of“new type”marine shale gas accumulation with low organic matter abundance in Wulalike Formation in the western Ordos Basin are studied,including the rock mineral composition,pore characteristics,organic geochemical characteristics and gas-bearing of shale.The results show that:(1)The shale mineral composition of Wulalike Formation is mainly felsic minerals,followed by carbonate minerals and clay minerals.The clay minerals are mainly illite and interlayer between illite and montmorillonite,followed by chlorite and kaolinite.(2)The porosity of Wulalike Formation is low(less than 2.0%),and the main reservoir space is intragranular pore and micro fracture,and the organic pore is not developed.The pore is mainly medium pore,and the pore development is controlled by lithology.(3)The organic matter type of shale belongs to type I-II1,in which type I(sapropel type)kerogen is the main type.The organic matter abundance is mainly 0.1%-3.71%,with an average of 0.49%;the vitrinite reflectance(RO)of organic matter is distributed in 0.8%-2.5%,most of them are at high-over mature stage,and there are certain differences in different regions.(4)The content of desorbed gas in the shale of Wulalike formation is 0.07-0.63 m^(3)/t,with an average of 0.3 m^(3)/t.The lost gas is recovered by USBM method.The lost gas is 0.43-1.83 m^(3)/t,with an average of 1.09 m^(3)/t.The total underground gas content is 0.76-2.46 m^(3)/t,with an average of 1.65 m^(3)/t,which reflects that the shale of Wulalike Formation has good adsorption capacity and reveals the marine facies of northern China shale has good shale gas exploration potential.