湘西北牛蹄塘组页岩气储层岩矿特征及意义

来源期刊:中南大学学报(自然科学版)2018年第6期

论文作者:郭建华 焦鹏 王玺凯 刘辰生 郭祥伟 黄俨然 刘博

文章页码:1447 - 1459

关键词:页岩气;储层;岩矿组分;牛蹄塘组;下寒武统;湘西北

Key words:shale gas; reservoir; components of rock and mineral; Niutitang formation; lower cambrian; northwest Hunan

摘    要:基于页岩矿物组成特征分析是页岩气储层评价的基础,也是影响页岩气成藏的关键因素,以湘西北下寒武统牛蹄塘组页岩为研究对象,在岩心观察的基础上,应用薄片鉴定、XRD、场发射扫描电镜和低温液氮等温吸附实验系统分析牛蹄塘组页岩的矿物组成特征及其意义。研究结果表明:湘西北牛蹄塘组页岩矿物组分复杂,具有“两低一高(石英质量分数高(41.40%~60.81%)、黏土矿物质量分数低(21.43%~26.40%)和碳酸盐矿物质量分数低(3.28%~16.10%)”的特点,此外,样品中还普遍含有方解石、斜长石、白云石、黄铁矿及钾长石等矿物;与国内外不同地区的页岩相比,湘西北下寒武统牛蹄塘组页岩脆性矿物种类丰富、质量分数高、脆性指数大,有利于储层的压裂改造;黏土矿物的组合类型反映了牛蹄塘组沉积时总体处于干冷气候条件下静水、缺氧的沉积环境,有利于页岩中有机质的富集和保存;在沉积及成岩埋藏过程中水介质偏碱性,盐度较高,富含K+,Fe2+和Mg2+;已经历晚成岩阶段B—C亚期,有机质演化属于高成熟—过成熟阶段;与矿物成分有关的储层孔隙主要是纳米级黏土矿物粒间孔、黄铁矿晶间孔以及微米级微裂缝,BJH总孔体积和BET比表面积经总有机碳归一化处理后,黏土矿物质量分数与BET比表面积呈正线性关系,表明黏土矿物质量分数对页岩的吸附性能有一定控制作用。

Abstract: Considering that the analysis of mineral composition of shale is the basis of shale gas reservoir’s evaluation as well as a key factor influencing accumulation of shale gas, Niutitang formation of lower Cambrian in Northwest Hunan was taken as the study object, mineral composition and its significance of Niutitang shale formation were systematically analyzed by section identification, XRD, field emission scanning electron microscopy(SEM) and low-temperature liquid nitrogen isothermal adsorption experiment. The results show that mineral components of Niutitang formation shale are diverse, which has a “two-low and one-high” characteristic (quartz content is high (mass fraction of 41.40%-60.81%) while clay minerals (mass fraction of 21.43%-26.40%) and carbonate minerals(mass fraction of 3.28%-16.10%) are low), in addition, these samples also generally contain calcite, plagioclase, dolomite, pyrite, potassium feldspar and other minerals. Compared with shale formations in different regions, Niutitang shale formation of lower Cambrian in Northwest Hunan has a property of diverse and abundant brittle minerals along with high brittleness index which is beneficial to reservoir fracturing. The combination of clay minerals reflects that Niutitang shale formation deposites in static water and hypoxia sedimentary environment under dry and cold climate condition, which is conducive to the enrichment and preservation of organic matter. The process of deposition and diagenetic burial goes through B-C substage of the late digenetic stage, water medium is basically alkaline which has high salinity of K+,Fe2+ and Mg2+, and the organic matter is at high and over mature stages. Reservoir pores related to mineral composition are nano-clay minerals intergranular pores, pyrite intergranular pores and micron-level cracks. BJH total pore volume and BET specific surface area are normalized by total organic carbon, and the clay mineral content is positively correlated with the BET specific surface area, indicating that the clay mineral content has effect on adsorption properties of shale.

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