致密砂岩中碳酸盐胶结物形成机制——以川西坳陷中段龙门山前沙溪庙组砂岩为例
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摘要
碳酸盐胶结物是川西坳陷中侏罗统沙溪庙组储集层最主要的胶结物,也是其储集层致密化主要因素之一,其中以龙门山前地区最为发育,其平均含量约为12%.以龙门山前沙溪庙组砂岩为研究对象,在样品微观观察的基础上,结合碳酸盐胶结物碳氧同位素分析、电子探针分析等手段,对其碳酸盐胶结物形成机制进行研究。通过分析,研究区沙溪庙组碳酸盐胶结物以连晶和微晶方解石为主,δ~(13)CPDB为-7.69‰~-2.13‰,以无机碳源为主,δ18OPDB为-15.34‰~-9.60‰,其形成温度为56.1~101.3℃,总体上形成于早成岩阶段。其中连晶方解石FeO和MnO含量均较低,少量微晶方解石富含FeO和MnO,表明其形成以早成岩阶段为主,但也发育有晚成岩阶段的方解石胶结物,其形成与来自深部富Fe和Mn的流体有关。
Carbonate cement is the most important cement in the reservoir of the Middle Jurassic Shaximiao formation in the western Sich-uan depression and is also one of the key factors of reservoir densification. Carbonate cement is very developed in the piedmont of Longmenmountain and its average content is about 12% in the area. Taking the sandstone of Shaximiao formation in the piedmont of Longmen moun-tain as the research object, the paper studies the formation mechanism of the carbonate cement based on the microscopic observation onsamples and the analysis of carbon and oxygen isotopes in the carbonate cement and electronic probe. The study shows that the carbonatecement in Shaximiao formation in the area is dominated by intergrown and microcrystalline calcites with the δ13 CPDBof-7.69‰~-2.13‰and the δ18 OPDBranging from-15.34‰ to-9.60‰. The inorganic carbon acts as the main source of the carbonate cement. The cementformed at the temperature of 56.1~101.3 ℃, indicating an early diagenesis stage. Relatively low FeO and MnO contents in the intergrowncalcites and relatively high FeO and MnO contents in a few microcrystalline calcites indicate that the carbonate cement was mainly formedat the early diagenesis stage. There are also some calcite cements developed at the late diagenesis stage whose formation is related to Feand Mn rich fluids in the deep strata.
Carbonate cement is the most important cement in the reservoir of the Middle Jurassic Shaximiao formation in the western Sich-uan depression and is also one of the key factors of reservoir densification. Carbonate cement is very developed in the piedmont of Longmenmountain and its average content is about 12% in the area. Taking the sandstone of Shaximiao formation in the piedmont of Longmen moun-tain as the research object, the paper studies the formation mechanism of the carbonate cement based on the microscopic observation onsamples and the analysis of carbon and oxygen isotopes in the carbonate cement and electronic probe. The study shows that the carbonatecement in Shaximiao formation in the area is dominated by intergrown and microcrystalline calcites with the δ13 CPDBof-7.69‰~-2.13‰and the δ18 OPDBranging from-15.34‰ to-9.60‰. The inorganic carbon acts as the main source of the carbonate cement. The cementformed at the temperature of 56.1~101.3 ℃, indicating an early diagenesis stage. Relatively low FeO and MnO contents in the intergrowncalcites and relatively high FeO and MnO contents in a few microcrystalline calcites indicate that the carbonate cement was mainly formedat the early diagenesis stage. There are also some calcite cements developed at the late diagenesis stage whose formation is related to Feand Mn rich fluids in the deep strata.
引文
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[2]李君,吴晓东,杨柏松,等.中国天然气聚集与分布新认识及有利勘探区带预测[J].新疆石油地质,2014,35(2):137-143.LI Jun,WU Xiaodong,YANG Baisong,et al. New understandings ofnatural gas accumulation and distribution with prediction of favor-able exploration plays in China[J]. Xinjiang Petroleum Geology,2014,35(2):137-143.
[3]刘四兵,黄思静,沈忠民,等.砂岩中碳酸盐胶结物成岩流体演化和水岩作用模式——以川西孝泉-丰谷地区上三叠统须四段致密砂岩为例[J].中国科学:地球科学,2014,44(7):1 403-1 417.LIU Sibing,HUANG Sijing,SHEN Zhongmin,et al. Diagenetic fluidevolution and water-rock interaction model of carbonate cements insandstone:an example from the reservoir sandstone of the Fourthmember of the Xujiahe formation of the Xiaoquan-Fenggu area,Sich-uan Province,China[J]. Science China:Earth Sciences,2014,44(7):1 403-1 417.
[4]刘春燕,郑和荣,胡宗全,等.碎屑岩中的碳酸盐胶结特征——以鄂尔多斯盆地南部富县地区延长组长6砂体为例[J].中国科学:地球科学,2012,42(12):1 681-1 689.LIU Chunyan,ZHENG Herong,HU Zongquan,et al. Characteristicsof carbonate cementation in clastic rocks from the Chang 6 sand-body of Yanchang formation,southern Ordos basin[J]. Science Chi-na:Earth Sciences,2012,42(12):1 681-1 689.
[5]魏巍,朱筱敏,国殿斌,等.查干凹陷下白垩统砂岩储层碳酸盐胶结物成岩期次及形成机理[J].地球化学,2015,44(6):590-599.WEI Wei,ZHU Xiaomin,GUO Dianbin,et al. Carbonate cements inLower Cretaceous Bayingebi sandstone reservoirs in Chagan sag,Yin-e basin:formation phases and formation mechanisms[J]. Geo-chimica,2015,44(6):590-599.
[6]付锁堂,王震亮,张永庶,等.柴北缘西段鄂博梁构造带储层碳酸盐胶结物成因及其油气地质意义——来自碳、氧同位素的约束[J].沉积学报,2015,33(5):991-999.FU Suotang,WANG Zhenliang,ZHANG Yongshu,et al. Origin ofcarbonate cements in reservoir rocks and its petroleum geologic sig-nificance:Eboliang structure belt,northern margin of Qaidam basin[J]. Acta Sedimentologica Sinica,2015,33(5):991-999.
[7]宋土顺,马锋,刘立,等.大庆长垣扶余油层砂岩中方解石胶结物的碳、氧同位素特征及其成因[J].石油与天然气地质,2015,36(2):255-261.SONG Tushun,MA Feng,LIU Li,et al. Features and genesis of car-bon-oxygen isotopes in calcite cement from sandstone in oil-bearingFuyu layer of Daqing placanticline[J]. Oil&Gas Geology,2015,36(2):255-261.
[8]叶瑛,沈忠悦,彭晓彤,等.塔里木盆地下第三系储层砂岩自生碳酸盐碳氧同位素组成及流体来源讨论[J].浙江大学学报(理学版),2001,28(3):321-326.YE Ying,SHEN Zhongyue,PENG Xiaotong,et al. C-O isotope com-position of the authigenic carbonate in Low Tertiary reservoir sand-stones in Tarim basin and its implication on the fluid origin[J]. Jour-nal of Zhejiang University(Science Edition),2001,28(3):321-326.
[9]王代富,罗静兰,陈淑慧,等.珠江口盆地白云凹陷深层砂岩储层中碳酸盐胶结作用及成因探讨[J].地质学报,2017,91(9):2 079-2 090.WANG Daifu,LUO Jinglan,CHEN Shuhui,et al. Carbonate cemen-tation and origin analysis of deep sandstone reservoirs in the Baiyunsag,Pearl River Mouth basin[J]. Acta Geologica Sinica,2017,91(9):2 079-2 090.
[10]韩元佳,何生,宋国奇,等.东营凹陷超压顶封层及其附近砂岩中碳酸盐胶结物的成因[J].石油学报,2012,33(3):385-393.HAN Yuanjia,HE Sheng,SONG Guoqi,et al. Origin of carbonatecements in the overpressured top seal and adjacent sandstones inDongying depression[J]. Acta Petrolei Sinica,2012,33(3):385-393.
[11]王大锐.油气稳定同位素地球化学[M].北京:石油工业出版社,2000.WANG Darui. Stable isotope geochemistry of oil and gas[M]. Bei-jing:Petroleum Industry Press,2000.
[12] FRIEDMAN I,O’NEIL J R. Compilation of stable isotope fraction-ation factors of geochemical interest[M]. U. S. Department of theInterior,1977,KK1-KK12.