Oil & Gas Geology ›› 2020, Vol. 41 ›› Issue (6): 1151-1161.doi: 10.11743/ogg20200604

• Petroleum Geology • Previous Articles     Next Articles

Alteration of reservoir-caprock systems by using CO2-rich fluid in the Huangqiao area, North Jiangsu Basin

Bing Zhou1,2(), Zhijun Jin1,2, Quanyou Liu1,2, Zengmin Lun1,2, Qingqiang Meng1,2, Dongya Zhu1,2   

  1. 1. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China
    2. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 100083, China
  • Received:2018-08-20 Online:2020-12-28 Published:2020-12-09

Abstract:

The mechanisms of CO2-rich fluid in the alteration of reservoir-caprock systems are worthy of study for understanding the links between hydrocarbon accumulation and CO2 activities, exploring the possibility of geological storage of CO2 and improving the effectiveness of enhanced oil recovery (EOR) with CO2 flooding.This study is focused on a comparison of reservoir-caprock systems with and without CO2 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 CO2 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 CO2-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 CO2-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 CO2-rich fluid led to precipitation of calcite and subsequent filling-up of cracks and pores in the caprocks, thus providing a better sealing effect.

Key words: alteration, interaction, sealing capacity, reservoir-caprock system, CO2-rich fluid, Huangqiao area, North Jiangsu Basin

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