Occurrence Mechanism and Key Controlling Factors of Wufeng-Longmaxi Shale Gas, Eastern Sichuan Basin
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摘要: 页岩气是重要的非常规天然气资源,主要以游离气与吸附气状态赋存于页岩中,研究和阐明其含量、主控因素和演化规律对于揭示页岩气成藏机理具有重要意义.采用不同条件下页岩高温高压等温吸附实验、FE-EM、CO2吸附、N2吸附、压汞等实验方法综合研究页岩气藏中的游离气与吸附气的主控因素.结果表明,游离气主要受页岩孔隙类型、孔隙结构、储层温度与压力等条件控制;OC、成熟度和水分影响吸附气含量.基于吸附气体积校正、地质模型和数值计算综合表征,五峰-龙马溪组页岩中以游离气为主,其平均含量约为%,吸附气含量约为4%.在抬升阶段,储层温度和压力发生改变,页岩气赋存形式随之变化,游离气减少,吸附气增加.Abstract: Shale gas is one important kind of natural resources, which occurs in reservoir by free state and absorbing state. In order to reveal its accumulation mechanism, it is significant to study and illuminate the TOC content, main controlling factors, evolution rule of shale gas. In this study, we analyze the main controlling factor of free gas and absorbed gas in reservoir comprehensively by high temperature and high pressure adsorption isothermal experiment, FE-SEM, CO2 adsorption experiment, N2 adsorption experiment and mercury injection experiment. The results show that free gas is controlled by pore types and pore structure of shale, temperature and pressure in reservoir; while absorbed gas is controlled by TOC, maturity and moisture. In different stages of hydrocarbon generation, the content of free gas and absorbed gas changes regularly. Free gas occurs in the highly mature stage, and increases the process of hydrocarbon generation and the evolution of pores. It transforms into absorbed gas in the lifting stage because of the changes of temperature and pressure, which results in free gas decrease and absorbed gas increase.
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Key words:
- shale gas /
- free gas /
- adsorbed gas /
- Jiaoshiba area /
- Wufeng Formation-Longmaxi Formation /
- petroleum geology
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图 1 焦石坝构造简图(a)和焦页1井地层柱状图(b)
据项目报告《焦石坝及其邻区页岩气富集机理》,中国石化集团南方勘探分公司,2014
Fig. 1. The regional tectonic of Jiaoshiba (a) and stratigraphic histogram of well JY1 (b)
表 1 样品参数及矿物成分
Table 1. Geochemical parameters and mineral components of shale samples
样品 深度(m) TOC(%) 粘土矿物(%) 石英(%) 钾长石(%) 斜长石(%) 方解石(%) 白云石(%) 黄铁矿(%) JY1-1 2 340.09 1.34 54.0 30.5 1.9 9.3 - - 4.3 JY1-2 2 361.44 2.09 33.5 33.1 2.1 10.8 5.9 9.9 4.7 JY1-3 2 375.06 2.08 36.0 32.5 3.5 11.8 3.5 9.9 2.8 JY1-4 2 384.18 2.98 34.5 38.2 3.3 8.6 5.9 5.8 3.7 JY1-5 2 404.43 4.09 35.1 42.7 2.0 7.2 6.5 3.7 2.8 JY1-6 2 414.56 6.45 38.0 36.6 5.7 9.1 1.9 5.6 3.1 表 2 抬升期计算的游离气与吸附气含量
Table 2. Free gas content and adsorbed gas content during the uplift
深度
(m)年代
(Ma)地层温度*
(K)地层压力α
(MPa)游离气
(m3/t·岩石)吸附气
(m3/t·岩石)5 500 100 473 79 3.16 1.35 4 500 60 403 60 3.06 1.52 2 414 0 358 36 2.58 1.60 注:地层温度*和地层压力α来自盆地模拟. -
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