准噶尔盆地AH5井区八道湾组碳酸盐胶结物成因及对储层影响分析

doi:10.19657/j.geoscience.1000-8527.2023.035

摘要/Abstract

摘要：

深入分析准噶尔盆地AH5井区侏罗系八道湾组储层碳酸盐胶结物形成原因,探讨碳酸盐胶结物对储层物性、含油性的影响,以指导后期储层评价及预测,本文综合运用岩石、铸体、荧光薄片以及碳酸盐胶结物的碳氧同位素等多种方法,对研究区碳酸盐胶结物的类型、形成期次、成因及其对储集层的影响进行研究。结果表明,研究区八道湾组至少存在两期碳酸盐胶结物,成岩早期碳酸盐胶结物以泥晶状菱铁矿和连晶状方解石为主,分布较为局限,其形成受控于凝灰质等易溶物质的溶蚀。晚期发育团粒状菱铁矿、铁方解石和铁白云石充填次生溶孔,铁白云石体积分数最大;晚期碳酸盐胶结物的δ¹³C_PDB分布于-13.6~-6.5‰,δ¹⁸O_PDB分布于-21~-18.1‰。通过古盐度和古温度的计算,发现碳酸盐胶结物的成岩流体为淡水环境,形成温度分布于112~136.1 ℃,推测形成于中成岩A期。结合碳图解和天然气同位素分析,碳酸盐胶结物中的碳来源主要为有机成因。通过物性资料、荧光薄片和胶结物含量分析,发现碳酸盐胶结的储层物性往往较差,以铁白云石为主的储层物性相对最好;同时碳酸盐胶结物体积分数越高,反映前期次生溶孔越多,含油性越好。

关键词: 碳酸盐胶结物, 成因机理, 八道湾组, AH5井区, 准噶尔盆地

Abstract:

To deeply investigate the genesis of carbonate cement in reservoirs of Jurassic Badaowan Formation in AH5 well block of the Junggar Basin, and to discuss the influence on the reservoir physical property and oiliness for evaluating/predicting reservoirs in later period, we studied the types, forming period, genesis and the influence on reservoir quality through combining thin-section petrography and carbon-oxygen isotope analyses in carbonate cement.The results show at least two periods of carbonate cement in the Badaowan Formation: micritic siderite and crystalline calcite in the early diagenetic stage (limited distribution), and granular siderite, ferrocalcite and ankerite developed in the late diagenetic stage (secondary dissolution pore infill), and ankerite has the highest volume.δ¹³C_PDB of carbonate cement=-13.6‰ to -6.5‰, and δ¹⁸O_PDB=-21‰ to -18.1‰.The paleosalinity and paleotemperature estimated from the carbon-oxygen isotope compositions show that the carbonate cement was formed in freshwater environment at 112 to 136.1 ℃, based on that the forming time was the middle diagenetic period.The carbon source in carbonate cement was of organic origin through carbon diagram and analysis on natural gas isotopes.Reservoirs with carbonate cement have always bad physical property, and reservoirs with ankerite cement have better physical property through combining physical property, fluorescence thin-section and carbonate cement content analysis.The higher volume of ankerite would have more early secondary dissolved pores and better reservoir oiliness.

Key words: carbonate cement, formation mechanism, Badaowan Formation, AH5 well block, Junggar Basin

中图分类号:

P618.13

于景维, 丁韦, 张欣, 祁利祺, 黄舒雅, 张智越, 张以勒. 准噶尔盆地AH5井区八道湾组碳酸盐胶结物成因及对储层影响分析[J]. 现代地质, 2023, 37(05): 1336-1344.

YU Jingwei, DING Wei, ZHANG Xin, QI Liqi, HUANG Shuya, ZHANG Zhiyue, ZHANG Yile. Genesis of Carbonate Cement and Influence on Reservoir Quality of the Badaowan Formation in AH5 Well Block of Junggar Basin[J]. Geoscience, 2023, 37(05): 1336-1344.

图/表 8

图1 准噶尔盆地构造图(a)、研究区位置图(b)和AH5井综合柱状图(c)[7] (a)图中:1.红岩断裂带;2.索索泉凹陷;3.石英滩凸起;4.英西凹陷;5.三个泉凸起;6.滴北凸起;7.夏盐凸起;8.三南凹陷;9.滴水泉凹陷;10.石西凸起;11.滴南凸起;12.达巴松凸起;13.盐1西凹陷;14.莫北凸起;15.东道海子凹陷;16.白家海凸起;17.草黄湖凸起;18.黑山凸起;19.梧桐窝子凹陷;20.乌夏断裂带;21.克百断裂带;22.中拐凸起;23.沙湾凹陷;24.莫南凸起;25.阜康凹陷;26.北三台凸起;27.吉木萨尔凹陷;28.古南凸起;29.古城凹陷;30.古东凸起;31.木垒凹陷;32.红车断裂带;33.车排子凸起;34.四棵树凹陷;35.齐古断裂带

Fig.1 Structural map of the Junggar Basin (a), structural location of the study area (b) and stratigraphic column of well AH5 (c)[7]

图2 研究区八道湾组储集岩石特征 (a)砂砾岩,AH501井,2835.32 m;(b)砂质砾岩,AH501井,2841.81 m;(c)砾岩,AH501井,2826.52 m;(d)含砾中-粗砂岩,AH501井,2869.36 m;(e)细-中砂岩,AH501井,2840.47 m;(f)储层砂岩三角投点图

Fig.2 Petrological characteristics of reservoirs in Badaowan Formation in the study area

图3 研究区八道湾组碳酸盐胶结物显微照片 (a)泥晶状菱铁矿,AH501井,2841.81 m;(b)团粒菱铁矿,局部沥青质充填,AH501井,2823.96 m;(c)连晶状方解石,AH501井,2883.55 m;(d)铁方解石交代长石,并充填粒间孔隙,MHHW15001井,2541.34 m;(e)铁白云石充填粒间孔隙和粒内溶孔,AH501井,2824.44 m;(f)铁白云石交代长石和岩屑,局部发育溶孔,局部沥青质充填,AH501井,2829.52 m

Fig.3 Thin-section photomicrographs of carbonate cement in Badaowan Formation in the study area

表1 研究区八道湾组碳酸盐胶结物C、O同位素组成

Table 1 Carbon and oxygen isotope compositions of carbonate cement in Badaowan Formation of the study area

样品号	碳酸盐胶结物类型	δ¹³C_PDB (‰)	δ¹⁸O_PDB (‰)	δ¹⁸O_SMOW (‰)	Z值	矿物形成温度 (℃)
AH501-1	团粒状菱铁矿	-10.30	-18.10	12.20	97.19	112.04
M625-1	团粒状菱铁矿	-11.20	-18.40	11.89	95.20	114.45
M625-2	铁方解石	-10.10	-19.50	10.76	96.90	123.44
M625-3	铁方解石	-11.20	-18.50	11.79	95.15	115.26
AH501-2	铁白云石	-13.60	-21.00	9.21	88.99	136.08
AH501-3	铁白云石	-10.30	-19.00	11.27	96.74	119.32
AH501-4	铁白云石	-7.50	-19.60	10.66	102.18	124.26
AH501-5	铁白云石	-10.60	-19.40	10.86	95.93	122.61
AH501-6	铁白云石	-10.10	-19.90	10.35	96.71	126.76
AH501-7	铁白云石	-6.50	-19.30	10.96	104.38	121.78

图4 研究区八道湾组储层碳酸盐胶结物成因判别图

Fig.4 Genetic discrimination plots of carbonate cement in Badaowan Formation of the study area

图5 研究区八道湾组埋藏史及成岩演化(AH5)

Fig.5 Buried history and diagenetic evolution of Badaowan Formation in the study area(AH5)

图6 研究区八道湾组胶结物垂向分布特征 (a)岩心,AH501井,2828.08~2830.6 m;(b)砾岩,铁白云石充填,AH501井,2830 m;(c)中砂岩,铁白云石充填,局部可见菱铁矿,AH501井,2829.52 m;(d)中砂岩,铁白云石和菱铁矿团块,AH501井,2828.94 m

Fig.6 Vertical distribution of carbonate cement in Badaowan Formation of the study area

图7 研究区八道湾组碳酸盐胶结物与储层含油性关系 (a) 碳酸盐胶结物体积分数与分形维数关系;(b) 岩石中胶结物呈现荧光显示,AH501井,2823.96 m

Fig.7 Relationship between carbonate cement and reservoir oiliness in Badaowan Formation of the study area

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