中扬子鄂西地区陡山沱组页岩气成藏地质条件与综合评价

Accumulation geological conditions and comprehensive evaluation of shale gas of Doushantuo Formation in western Hubei Province,middle Yangtze area

利用钻井、露头剖面及测试资料,对鄂西地区震旦系陡山沱组岩性发育、沉积相展布、页岩气成藏地质条件进行了综合分析,并对页岩气富集规律进行了总结。研究区陡山沱组可划分为4段,其中陡二段黑色碳质白云岩为主要页岩气储层。陡二段由西至东主要发育浅水陆棚、台盆及台地相,厚度中心主要位于秭归—五峰一带,富有机质的地层厚度超过100 m。陡二段富有机质地层的TOC主要介于0.5%~2.0%,为低—中等含量,TOC大于1.0%的区域分布在神农架林区—秭归—五峰一带;R_(o)以2.0%~3.5%为主,有机质处于过成熟阶段。陡二段岩石矿物组分以白云石为主,岩相类型主要为灰质页岩相,为特低—低孔隙度、特低渗透率页岩储层,微观孔隙主要为白云石粒间孔和黏土矿物层间孔,黄铁矿晶间孔和有机质孔在TOC高的样品中较发育。含气性较好的区域仅局限于黄陵背斜南翼及天阳坪断裂以北地区,现场解吸气含量平均可达1.0 m^(3)/t。认为陡山沱组页岩气成藏主要受到沉积相和构造类型的叠加影响,台盆相内、单斜稳定构造带、逆断层下盘、远离区域性正断层且埋深超过2000 m的区域有利于页岩气成藏,有利区主要分布于黄陵背斜东南缘的阳页1井区以及宜页1—宜地3井区的周缘。

The geological conditions of shale gas accumulation,gas-bearing characteristics and shale gas preservational conditions of Doushantuo Formation in western Hubei Province was studied based on comprehensive analysis of drilling,outcrops,and testing data.The Doushantuo Formation in the study area can be divided into four members,and the black carbonaceous dolomite developed in the second Member of Doushantuo Formation(Z_(1)d_(2))is the main shale gas reservoir.From west to east,the shallow shelf,basin and platform facies are developed in turn,and two isolated platform are developed among the basin.On the plane,the depocenter is mainly developed in Zigui-Wufeng region,with the thickness of organic-rich strata more than 100 m;the areas with the TOC values greater than 1.0%are distributed in the Shengnongjialinqu-Zigui-Wufeng area.Overall,the TOC values are at the range of 0.5%-2.0%belonging to low to medium level,and R_(o) is mainly high maturity of 2.0%-3.5%.The Z_(1)d_(2) is characterized by the dominated dolomite mineral,the calcareous shale,the ultralow-low porosity,and ultra-low permeability reservoir.The dolomite intergranular pores and clay mineral stratified pores are the most important pore types,and pyrite intercrystalline pores and organic matter pores are much more developed in the samples with high TOC value.The areas with the high gas content are limited only to the north of the Tianyangping fault and southern of the Huangling anticline with the gas content over 1.0 m^(3)/t.It is believed that the shale gas accumulation in Doushantuo Formation is mainly influenced by the superposition of sedimentary facies and structural types.Basin and platform basin facies,stable structural belt,the footwall of reverse fault,and the area far away from regional normal faults with a buried depth of more than 2,000 m are conducive for shale gas accumulation.This paper also provide a scientific basis for further shale gas exploration and development of the Doushantuo Formation in western Hubei Province.It is proposed that favorable areas are mainly distributed in the Yangye-1 well block and Yiye-1 to Yidi-3 well block in the southeast margin of Huangling anticline.