中国石油大学学报（自然科学版）2024，Vol.48Issue(2)：24-36,13.DOI:10.3969/j.issn.1673-5005.2024.02.003
鄂尔多斯盆地西南缘浅埋藏储层致密化成因
Mechanism of tight sandstone reservoirs with shallow burial in southwest of Ordos Basin
摘要
Abstract
The densification of fine sandstone occurred under relatively shallow burial conditions in the 8th member of the TrassicYanchang Formation,deposited in the Zhenyuan area of the southwest Ordos Basin.The pore-throat structure and dia-genesis of Chang 8 member tight reservoir were analyzed through core analysis,casting thin sections,scanning electron mi-croscope,fluorescence thin section with picture analysis,and other methods.The results indicate that both compositional and structural maturity are relatively low,with the dominant pore-throat structure being fine pores with minimal throats.Diagenesis is characterized by strong compaction,multi-period cementation,and dissolution accompanied by variations in the diagenetic environment.The quantitative characterization of densification process was carried out under the comprehensive control of"burial history-oil and gas filling history-diagenetic evolution sequence-pore-throat structure".It reveals that Chang 8 mem-ber contains a large amount of fine grains and plastic fragments with a high matrix content,leading to significant reservoir space loss under rapid burial after deposition.This was influenced by a stable tectonic setting combined with a braided river delta sedimentary system,resulting in strong compaction contributing to 85%of the densification.Additionally,pore fluids saturated with various salts led to intense cementation,affected seriously by multiple changes in the diagenetic environment,contributing 40.8%to the densification.The early-formed chlorite film protected clastic particles from being dissolved.Cement layers limited the exchange of pore fluid with surrounding rock under the stable tectonic background,which were formed at the roof and floor of Chang 8 member by strong siliceous cementation and carbonate cementation.Early entry into a low-permeabili-ty stage,coupled with distance from the hydrocarbon-generating center of the basin,hindered continuous acid fluid injection,reducing the dissolution intensity.Consequently the inhibiting effect of dissolution on densification was only 26.1%.Besides,the secondary pores generated by dissolution were easily filled by later-period cements.In summary,the tight sandstone reser-voirs in the Chang 8 member were buried at shallow depths,controlled by multiple factors,including tectonic setting,sedimen-tary environment,diagenesis,and their coupled relationship with periods of hydrocarbon generation and expulsion.关键词
镇原地区/延长组8段/致密砂岩/致密化/定量表征/成岩环境Key words
Zhenyuan area/8th member of Yanchang formation/tight sandstone/densification/quantitative characteriza-tion/diagenetic environment分类
地质学引用本文复制引用
张英男,白青林,束青林,路智勇,张戈,窦祥骥,李真,何之明..鄂尔多斯盆地西南缘浅埋藏储层致密化成因[J].中国石油大学学报（自然科学版）,2024,48(2):24-36,13.基金项目
江苏省基础研究计划自然科学基金项目(BK20220623) （BK20220623）
江苏省高等学校自然科学研究项目(20KJB440003) （20KJB440003）
