鄂东通山地区下寒武统牛蹄塘组富有机质页岩矿物组成及意义

Mineral Composition and Its Significance of Organic Shale of the Lower Cambrian Niutitang Formation in Tongshan Area,Eastern Hubei

中扬子地区作为中国南方重要的页岩气资源勘探开发接替区,正逐渐成为研究开发的热点。但不同地区、不同层系的研究和认识程度不一。鄂东通山地区下寒武统牛蹄塘组富有机质泥页岩的沉积及矿物特征,目前研究程度较低,为进一步勘查研究与评价该区页岩气资源,野外实测了界水岭和珍珠口剖面并选取露头样品进行X射线衍射分析。结果表明:该牛蹄塘组矿物成分较为复杂,类型多样。石英含量最高,含量为31.9%~47.2%,平均42.1%。黏土矿物含量为18.3%~21.9%,平均20.6%。碳酸盐矿物中以方解石含量变化最大,含量为1.3%~27.5%,平均值为15.1%。长石平均含量为12.0%,主要成分为斜长石。微晶矿物石膏在样品中普遍存在。黏土矿物主要成分为伊利石,平均含量达63.9%,其次为绿泥石和伊/蒙混层,含极少量高岭石,不含蒙脱石。沉积过程及埋藏成岩过程中水介质总体处于缺氧的还原环境,并已进入晚成岩阶段。脆性矿物含量为62.3%~76.3%,平均69.73%,脆性指数为0.74~0.81,平均0.77,脆性指数与脆性矿物含量有着很好的对应性;矿物组成及含量与周边地区、威远、涪陵以及北美页岩气田有着很好的对比性。参考北美及焦页1井储层优选条件,认为研究区下寒武统牛蹄塘组具备页岩气藏的形成和保存的基础地质条件,有着很好的可压裂性,具备一定的开采潜力。

As an important replacement area for shale gas exploration and development in South China,the middle Yangtze region is gradually becoming a hot spot of research and development.However,the degree of research and understanding varies in areas and strata.The sedimentary and mineral characteristics of organic-rich shale in Niutitang Formation of the Lower Cambrian in Tongshan area,eastern Hubei Province,are poorly studied.To further explore and evaluate shale gas resources in this area,Jieshuiling and Zhenzhukou Sections were measured and samples collected for X-ray diffraction analysis.The results show that the mineral composition of the Niutitang Formation is complex with various types.The content of quartz is the highest,ranging from 31.9%to 47.2%,on average of 42.1%;the content of clay minerals ranges from 18.3%to 21.9%,on average of 20.6%;the content of calcite varies greatly,ranging from 1.3%to 27.5%,on average of 15.1%.The average content of feldspar is 12.0%,and the main component is plagioclase.Microcrystalline mineral gypsum is common in the samples.The clay mineral is mainly composed of illite,on average content of 63.9%,followed by chlorite and illite/montmorillonite mixture,with little kaolinite and no montmorillonite.The above mineral assemblages indicate that the water medium is in anoxic reducing environment during sedimentation and burial diagenesis,and has entered the late diagenetic stage.The content of brittle minerals ranges from 62.3%to 76.3%,on average of 69.73%.The brittleness index ranges from 0.74 to 0.81,on average of 0.77;there is a good correspondence between the brittleness index and the content of brittle minerals.The mineral composition and content have a good contrast with the shale gas fields in the surrounding areas and Weiyuan and Fuling of China,and North American.Referring to the reservoir optimization conditions of North America and Jiaoye#1 Well,it is considere that the Niutitang Formation in the study area meets the basic geological conditions for the formation and preservation of shale gas reservoir,has good fracturability,and has certain exploitation potential.