摘要
通过长时间储层温度下页岩气现场解吸实验,揭示页岩气析出过程中气体赋存状态变换与气体组分及甲烷H、C稳定同位素的关联性。结果表明,与解吸气甲烷C同位素(δ^(13)C_(1))早期变化幅度较小、后期持续变重的现象不同,甲烷H同位素(δD(CH_(4)))具有先变轻后变重的规律,且在解吸至40%~50%阶段后与δ^(13)C_(1)变重同步。依据δD(CH_(4))变化规律及页岩含气性、气体渗流特征,可将页岩气析出过程划分为游离气压差渗流、游离气渗流–吸附气解吸扩散共存和吸附气解吸扩散3个阶段:阶段Ⅰ裂隙及基质孔隙中的游离气在压差作用下渗流,产出页岩气的δD(CH_(4))和δ^(13)C_(1)基本不变;阶段Ⅱ游离气渗流与吸附气解吸扩散共存,质量较轻的12CH_(4)优先脱附,吸附气的补给使产出气体的δD(CH_(4))显著变轻(变轻4‰~10‰),而δ^(13)C_(1)变轻的现象不显著;阶段Ⅲ析出的气体主要来自吸附气解吸,受吸附–解吸和扩散作用的共同影响,产出气体的δD(CH_(4))(变重15‰~20‰)和δ^(13)C_(1)(变重21.9‰~32.9‰)显著变重。δD(CH_(4))对页岩气析出过程气体赋存状态变换的响应比δ^(13)C_(1)更敏感和有效,因此有望建立一种基于页岩气析出过程中δD(CH_(4))变化规律预测页岩气产量的定量评价方法。
On the basis of the long-term canister desorption of gas shales at the reservoir temperature,the variation of shale gas occurrence and its relationship with the hydrogen and carbon isotopes of CH_(4) during shale gas release are studied.The results show that theδD(CH_(4))values of the desorbed gas become lighter first and then heavier as desorption proceeds at the reservoir temperature,whereas theδ^(13)C_(1) values keep unchanged first and become heavier subsequently.BothδD(CH_(4))andδ^(13)C_(1) values become heavier once 40%to 50%of the shale gas is desorbed.Based on the variation ofδD(CH_(4))values and shale gas-bearing and seepage characteristics,the release process of shale gas can be divided into three stages:free gas seepage under differential pressure,free gas seepage as well as desorbed gas diffusion,and diffusion of desorbed gas.In stageⅠ,the released shale gas comes from the free gas stored in the matrix-associated pores and fractures,and theδD(CH_(4))andδ^(13)C_(1) values of the released gas remain unchanged.During stageⅡ,both free gas seepage and desorbed gas diffusion exist and the extra supply of desorbed 12CH_(4) makesδD(CH_(4))of released gas lighter(decreased by 4‰to 10‰)while itsδ^(13)C_(1) values change little.During the stageⅢ,the desorbed gas comprises the released gas,both theδD(CH_(4))andδ^(13)C_(1) values of the released gas increase from 15‰to 20‰and 21.9‰to 32.9‰,respectively,which are controlled by the effect of adsorption-desorption and diffusion.Our results show that the response ofδD(CH_(4))to the change in shale gas occurrence during shale gas release is more sensitive and effective thanδ^(13)C_(1),so it is promising to establish a novel quantitative evaluation method for predicting shale gas production based on the variation of the hydrogen isotope of CH_(4).
作者
马勇
李大华
黄越
罗彤彤
汪生秀
张海鹏
钟宁宁
MA Yong;LI Dahua;HUANG Yue;LUO Tongtong;WANG Shengxiu;ZHANG Haipeng;ZHONG Ningning(National Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum(Beijing),Beijing 102249,China;Key Laboratory of Shale Gas Exploration(Chongqing Institute of Geology&Mineral Resource),Ministry of Natural Resources,Chongqing 401120,China;Geological Exploration and Development Research Institute of Chuanqing Drilling Engineering Co.,Ltd.,Chengdu 610056,Sichuan,China)
出处
《地球化学》
CAS
CSCD
北大核心
2024年第2期163-173,共11页
Geochimica
基金
国家自然科学基金项目(41802149、42173030)
重庆市自然科学基金面上项目(cstc2021jcyj-msxmX0624)
重庆页岩气公司科研专项(CYS-FW-2020-0047)联合资助。
关键词
页岩气
H同位素
C同位素
同位素分馏
赋存状态
shale gas
hydrogen isotope
carbon isotope
isotopic fractionation
occurrence
