基于激光U-Pb定年技术的白云岩储集层形成过程恢复--以鄂尔多斯盆地奥陶系马家沟组为例  

Restoration of formation processes of dolomite reservoirs based on laser U-Pb dating:A case study of Ordovician Majiagou Formation,Ordos Basin,NW China

作　　者：周进高 于洲 吴东旭 任军峰[3] 张道锋[3] 王少依 尹陈 刘雨昕 ZHOU Jingao;YU Zhou;WU Dongxu;REN Junfeng;ZHANG Daofeng;WANG Shaoyi;YIN Chen;LIU Yuxin(PetroChina Hangzhou Research Institute of Geology,Hangzhou 310023,China;CNPC Key Laboratory of Carbonate Reservoir,Hangzhou 310023,China;PetroChina Changqing Oilfield Company,Xi'an 710018,China;China University of Petroleum(Beijing),Beijing 102249,China)

机构地区：[1]中国石油杭州地质研究院,杭州310023 [2]中国石油天然气集团有限公司碳酸盐岩储层重点实验室,杭州310023 [3]中国石油长庆油田公司勘探开发研究院,西安710018 [4]中国石油大学(北京),北京102249

出　　处：《石油勘探与开发》2022年第2期285-295,共11页Petroleum Exploration and Development

基　　金：国家科技重大专项“寒武系—中新元古界碳酸盐岩规模储层形成与分布研究”(2016ZX05004-002);中国石油天然气股份有限公司科技专项“长庆油田5000万吨持续高效稳产关键技术研究与应用”(2016E-05-14);中国石油天然气股份有限公司科技重大项目“海相碳酸盐岩有效储层形成与保持机理及分布预测研究”(2021DJ0503)。

摘　　要：针对以往定性或半定量研究白云岩储集层形成过程所取得的认识存在争议的问题,以鄂尔多斯盆地奥陶系马家沟组为例,应用激光U-Pb原位定年技术,并结合碳氧同位素组成等分析测试数据,对马家沟组风化壳岩溶型和丘滩型两类白云岩储集层形成过程进行研究。结果如下:①8个储集层样品定年测试显示马家沟组主要经历了5期成岩作用,第1期为基质白云岩的沉积或准同生期白云石化作用,发生时间为距今444.0~494.0 Ma,第2期为犬牙状或叶片状白云石胶结作用,发生时间为距今440.0~467.0 Ma,第3期为白云石粉砂充填作用,发生时间为距今316.5~381.0 Ma,第4期为晶粒白云石充填作用,发生时间为距今354.0 Ma,第5期为晶粒方解石充填作用,发生时间为距今292.7~319.0 Ma;②马家沟组基质白云岩的形成与沉积或准同生期白云石化作用有关,而胶结物的白云石化稍晚,属渗透回流—早埋藏期白云石化作用成因;③盐上风化壳岩溶型白云岩储集层依次经历准同生白云石化、压实、风化壳岩溶、充填与破裂等成岩作用,膏模孔形成于表生岩溶阶段,被白云石粉砂和方解石等矿物充填,孔隙度由10%~40%降低至3%~8%;④盐下丘滩型白云岩储集层经历准同生白云石化、压实、海底胶结、准同生溶蚀、渗透回流白云石化、充填和破裂等成岩作用,储集层原生孔隙度为10%~30%,经海水胶结作用后降至0~6%,准同生溶蚀作用使孔隙度恢复至5%~15%,之后由晶粒白云石和方解石充填,孔隙度最终降至2%~6%。上述基于激光原位定年技术的白云石化作用和孔隙演化恢复方法对其他盆地或层系储集层孔隙演化恢复具有一定借鉴意义。To address the issue of non-unique interpretation of dolomite reservoir diagenetic and porosity evolution in the previous qualitative or semi-quantitative studies,we investigate two dolomite reservoir types,i.e.weathering-crust karstic reservoirs and mound-beach reservoirs,in the Ordovician Majiagou Formation,the Ordos Basin using in-situ laser ablation U-Pb dating as well as carbon and oxygen isotopic composition analysis.The results show that:(1)According to the dating of 8 reservoir samples,the Majiagou Formation experienced 5 diagenetic stages(Stage 1:deposition of matrix dolomite or penecontemporaneous dolomitization,in 444.0–494.0 Ma;Stage 2:dogtooth-or blade-shaped dolomite cementation,in 440.0–467.0 Ma;Stage 3:dolomitic silt filling,in 316.5–381.0 Ma;Stage 4:crystalline dolomite filling,in 354.0 Ma;Stage 5:crystalline calcite filling,in 292.7–319.0 Ma).(2)Supra-salt weathering-crust karstic dolomite reservoirs went through several diagenetic processes including penecontemporaneous dolomitization,compaction,weathering-crust karstification,packing,and rupturing in succession.Gypsum mold pores formed in the phase of hypergenic karstification and were filled with such minerals as dolomitic silts and calcites,and thus the porosity decreased from 10%–40%to 3%–8%.(3)Sub-salt mound-beach dolomite reservoirs went through the diagenetic processes including penecontemporaneous dolomitization,compaction,subsea cementation,penecontemporaneous corrosion,infiltration backflow dolomitization,packing,and rupturing.The porosity of reservoirs was originally 10%–30%,decreased to 0–6%due to seawater cementation,rose back to 5%–15%owing to penecontemporaneous corrosion,and finally declined to 2%-6%as a result of crystalline dolomites and calcites packing.The above methodology for the restoration of dolomitization and porosity evolution may be helpful for the restoration of porosity evolution in other basins or series of strata.

关 键 词：U-Pb定年 鄂尔多斯盆地 奥陶系 马家沟组 成岩作用 白云石化 孔隙演化 

分 类 号：TE122[石油与天然气工程—油气勘探]