海陆过渡相页岩气聚集条件及勘探潜力研究——以黔北地区金沙参1井龙潭组为例

Accumulation condition and shale gas potential of the marine- terrestrial transitional facies:A case study of Jinshacan 1 well of Longtan formation in northern Guizhou

为了深入了解黔北地区上二叠统龙潭组海陆过渡相页岩气聚集条件及勘探潜力,以贵州林华矿区页岩气参数井金沙参1井为例,采用薄片鉴定、X-射线衍射分析、有机地化、覆压孔渗、扫描电镜、低温氮吸附、现场解析及甲烷等温吸附等实验测试方法,结合实际地层地质条件,研究了龙潭组页岩气聚集条件,综合考虑页岩气发育的关键地质参数,认为层段一含较厚的黑色炭质页岩、有机碳含量高、黏土矿物含量较低、脆性较好、含气量高,资源潜力大,勘探条件好,为最优勘探层段.研究结果表明:1)黔北地区龙潭组泥页岩单层厚度薄、累计厚度较大(约44.65 m),与砂岩、煤层互层出现;2)泥页岩有机碳含量高(TOC平均为4.20%)、热演化程度较高(Ro平均为2.53%),黏土矿物含量较高(质量分数平均为46.41%)、石英次之(质量分数平均为28.34%),泥页岩脆性指数整体较高,发育粒间孔、粒内孔、微裂缝及有机质孔,比表面积、总孔体积较大,以中孔为主,泥页岩现场解析含气量较高(平均为3.25 m^3/t),饱和吸附气量较高(平均为2.33 m^3/t),含气性较好,具有良好的页岩气聚集条件;3)TOC是泥页岩含气性的主控因素,现场解析含气量和饱和吸附气量均与TOC呈良好的正相关,含气量与BET比表面积呈较好的正相关,泥页岩饱和吸附气量与黏土矿物含量、BET比表面积均呈较好的正相关;4)金沙参1井位于新化向斜西翼靠轴部端,表现为向斜控藏下的原地型页岩气富集模式,构造稳定,后期改造程度较低,保存条件较好;综合考虑各项页岩气发育地质参数,将龙潭组自下而上划分为3个层段,并结合砂岩、煤层发育特点,揭示出较好的页岩气勘探前景.

In order to detailly study the accumulation and shale gas potential of the marine-terrestrial transitional facies in Longtan formation of Upper Permian in northern Guizhou, this study take an example of Jinshacan 1 well in the Linhua Mine of Guizhou province, multiple methods, including thin section identification, X-ray diffraction analysis, organic geochemistry, overburden pressure porosity and permeability, scanning electron microscopy, low temperature nitrogen adsorption, field gas desorption analysis and isothermal adsorption, combined with the realistic geological conditions, the accumulation, preservation and shale gas potential of the Longtan shale were studied. Given the key geological parameters of shale gas development, the system of parameter optimization and the favorable exploration intervals of shale gas formation were proposed. The results indicate that:(1) the Longtan shale in northern Guizhou is characterized by multiple thin monolayer, large in accumulated thickness(about 44.65 m), and interbedded with sandstone and coal seam;(2) high organic matter content(TOC averaged 4.20%) and thermal maturity(R_o averaged 2.53%), clay minerals(w(clay) averaged 46.41%) contribute to the largest proportion of mineralogical composition, which is followed by quartz(w(quartz) averaged 28.34%), the overall brittleness index of the Longtan shale are moderate to high, intergranular and intragranular pores, microcracks as well as organic matter pores are developed, with large specific surface area and total pore volume, pores are dominated by mesopores, the in-situ analytical gas content of shale is high(averaged 3.25 m^3/t), and the saturated adsorption gas volume is high(averaged 2.33 m^3/t) and it contains significant amount of gas, therefore, the Longtan Shale showed favorable shale gas accumulation conditions;(3) TOC is the primary control on gas content of shales, this is supported by good and positive correlations between TOC and field desorbed gas content as well as the maximum adsorbed gas content derived from methane sorption measurements;(4) Jinshacan 1 well is geologically located on the west wing of Xinhua syncline, which shows the in-situ shale gas enrichment mode under syncline controlled reservoir, stable structure during geological history is beneficial for the preservation of shale gas;given the key geological parameters of shale gas development, the Longtan formation is divided into three intervals from bottom to top, and combined with the development characteristics of coal seam and sandstone, a better shale gas exploration potential is revealed.