摘要
中国南方古生界烃源岩的原始干酪根类型以腐泥型-偏腐泥型(Ⅰ-Ⅱ型)为主,目前主体处于过成熟阶段(镜质体反射率R_(o)>2.0%),准确评价Ⅰ-Ⅱ型干酪根在生-排油之后的生气潜力(或晚期生气)及生气特征对中国南方古生界深层-超深层天然气勘探至关重要。鉴于此,以川西北地区中泥盆统观雾山组样品(R_(o)≈1.1%)为例,通过黄金管生烃模拟实验,结合已有文献资料,探讨了Ⅰ-Ⅱ型干酪根在高-过成熟阶段的生气潜力及气体地球化学特征。结果表明,研究样品残留油含量(按单位有机碳质量计算,以下同)为140 mg/g,现今生气潜力为220 mL/g,显示仍具有较好的生气潜力。其中,干酪根裂解气的贡献至少为140 mL/g,残留油裂解气最多为80 mL/g,表明腐泥型烃源岩在排油效率较高时,其晚期生气以干酪根裂解气为主。同时,排油之后的腐泥型烃源岩晚期生成的天然气干燥系数较高,随着甲烷产率的增加甲烷碳同位素快速变重,在成熟度达到R_(o)≈3.5%时,其甲烷碳同位素值与母质干酪根碳同位素值接近(碳同位素分馏程度约为0.5‰)。上述结果可为中国南方古生界深层-超深层天然气的资源潜力评价和天然气来源识别等研究提供有益的科学依据。
The Paleozoic source rocks in southern China contain mainly TypeⅠ-Ⅱkerogen and are currently overmature with vitrinite reflectance (R_(o)) greater than 2.0%.Accurate evaluation of the gas generation potential of TypeⅠ-Ⅱkerogen after oil generation and expulsion and geochemical characteristics of over-mature gases are of great significance to natural gas exploration of deep and ultra-deep Paleozoic gas pools in southern China.In view of this,the mature Devonian source rock samples (R_(o)≈1.1%) collected from the Guanwushan Formation in Northwestern Sichuan Basin are applied for gold tube pyrolysis experiments,and the gas generation potential of TypeⅠ-Ⅱkerogen at the highto-over mature stage and the geochemical characteristics of over-mature gas generated are investigated in combination with existing documents.The results show that the residual oil content of the studied samples is 140 mg/gTOC and has a gas generation potential of 220 mL/gTOC at present,indicating high gas-generation potential.Furthermore,the amount of gas from kerogen cracking is at least 140 mL/gTOC and that of gas from residual oil cracking is at best 80 mL/gTOC,indicating that kerogen-cracking gas is the main source of late gas generated from the sapropelic source rocks under high oil expulsion efficiency.Meanwhile,the geochemical characteristics of the late gases generated from the sapropelic source rocks are obviously affected by oil expulsion efficiency.For example,the dryness coefficient of the gases is high,and the methane carbon isotope grows heavier rapidly with increasing methane yield.At R_(o)≈3.50%,the carbon isotope of methane is close to that of the original kerogen (with a mere carbon isotopic fractionation difference of 0.5‰).The results obtained above will be of scientific basis to the evaluation of natural gas exploration potential and the identification of natural gas sources in the deep and ultra-deep Paleozoic reservoirs in southern China.
作者
田辉
吴子瑾
盖海峰
王星
TIAN Hui;WU Zijin;GAI Haifeng;WANG Xing(State Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,CAS,Guangzhou,Guangdong 510640,China;Center for Excellence in Deep Earth Science,CAS,Guangzhou,Guangdong 510640,China)
出处
《石油与天然气地质》
EI
CAS
CSCD
北大核心
2023年第1期46-54,共9页
Oil & Gas Geology
基金
中国科学院A类战略性先导科技专项(XDA14010104)
国家自然科学基金杰出青年科学基金项目(41925014)。
关键词
干酪根裂解气
甲烷碳同位素
腐泥型烃源岩
晚期生气
深层天然气
中泥盆统
川西北地区
gas from kerogen cracking
methane carbon isotope
sapropelic source rock
late gas generation
deep natural gas
Middle Devonian
Northwestern Sichuan Basin
