苏北盆地黄桥地区富CO流体对油气储-盖系统的改造作用

Alteration of reservoir-caprock systems by using CO-rich fluid in the Huangqiao area, North Jiangsu Basin

周冰 金之钧 刘全有 伦增珉 孟庆强 朱东亚

Bing Zhou Zhijun Jin Quanyou Liu Zengmin Lun Qingqiang Meng Dongya Zhu

查明富CO流体对储-盖系统的改造作用，对于研究CO活动与油气成藏效应、CO储存和CO驱油提高采收率有着重要意义。选取下扬子苏北盆地黄桥地区和句容地区的二叠系龙潭组储层和大隆组盖层组合，分别作为有无CO流体活动的对比研究对象。通过薄片观察统计、矿物成分和碳同位素分析，查明了两个地区储层的异同点。黄桥地区储层的自生矿物以石英次生加大边和高岭石充填为主，发育少量片钠铝石，句容地区不发育片钠铝石，且次生石英含量不高；黄桥地区储层孔隙度明显高于句容地区，薄片下观察到大量长石溶蚀孔隙，偶见长石溶蚀孔内生长片钠铝石雏晶，是CO与长石发生水岩相互作用的直接证据；黄桥地区和句容地区盖层均为黑色块状泥岩，黄桥地区盖层发育微裂隙，但裂隙均已再充填方解石脉，碳同位素数据表明方解石脉为富CO流体活动结果，在句容地区泥岩盖层中未见大量裂隙和矿物脉。综合研究分析表明，富CO流体充注引起储层砂岩中长石大量溶蚀，增加了孔隙空间，片钠铝石、次生石英和高岭石自生矿物组合序列沉淀，同时富CO流体的连续活动导致泥岩盖层发生方解石沉淀，充填盖层裂缝，有利于提高盖层的封盖能力。

The mechanisms of CO-rich fluid in the alteration of reservoir-caprock systems are worthy of study for understanding the links between hydrocarbon accumulation and CO activities, exploring the possibility of geological storage of CO and improving the effectiveness of enhanced oil recovery (EOR) with CO flooding.This study is focused on a comparison of reservoir-caprock systems with and without CO fluid activities in the Longtan and Dalong Formations of the Permian in the Huangqiao and Jurong areas, North Jiangsu Basin, Lower Yangtze region.The results based on thin sections observation, mineral composition and carbon isotope analyses of the areas show that the authigenic minerals in the reservoirs of the Huangqiao area are dominated by secondary overgrowth of quartz and kaolinite, followed by a small amount of dawsonite, whereas those in the Jurong area contain no dawsonite at all and have only limited amount of secondary quartz.The reservoir porosity of the Huangqiao area is markedly higher than that of the Jurong area.Thin section observation reveals a large number of dissolved pores in feldspar occasionally with dawsonite in samples from the Huangqiao area—a piece of direct evidence of interaction between CO and feldspar.Both caprocks in the two areas are black blocky mudstones.There are micro-cracks refilled with calcite veins in the caprocks of the Huangqiao area.And carbon isotope data show that the calcite veins are the result of CO-rich fluid activities.While few cracks and mineral veins are discovered in the mudstone caprocks from the Jurong area.These results indicate that the charging of CO-rich fluid in the reservoirs caused large-scale dissolution of feldspar, which increased pore space and precipitation of typical authigenic mineral assemblages of dawsonite, secondary quartz and kaolinite.The continuous activities of the CO-rich fluid led to precipitation of calcite and subsequent filling-up of cracks and pores in the caprocks, thus providing a better sealing effect.

10.11743/ogg20200604