Shale reservoir characteristics of Ordovician Wufeng-Silurian Longmaxi formations in Dangyang synclinorium, Middle Yangtze region
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摘要: 以当阳复向斜内典型井钻井资料为基础,通过双束扫描电镜、矿物含量分析、有机地球化学分析和低温低压氮气吸附测定等方法,对富有机质页岩岩石学特征、有机地球化学特征、储集空间类型及特征和含气性特征等进行系统研究。研究结果表明:①五峰组-龙一1亚段页岩储层在纵向上差异较大,优质页岩储层发育在龙一11小层-龙一12小层,其有机质丰度高(2.45%~6.98%)、有机质类型好(Ⅱ1-Ⅱ2型)、热演化程度较高、脆性矿物含量高(34%~85.5%)、黏土矿物含量低(9%~40.3%)、总含气量高(1.76~4.30 m3/t),有机孔非常发育;进入龙一13小层后,受到加里东运动构造活动加剧的影响,陆源输入量增大,储层品质开始变差。②在横向上,当阳复向斜内由东南向西北方向,五峰组-龙马溪组富有机质页岩越来越发育,储层品质越来越好。③研究区龙一11小层-龙一12小层页岩储层具有"最甜"和"最脆"的特征,但考虑到水平段钻进过程中需要对井轨迹进行实时监控与调整,应选择龙一11小层内GR峰的上下半幅点之间作为水平井的最佳水平箱体。Abstract: The petrological and organic geochemical characteristics, reservoir porosity types and features, and gas-bearing characteristics of organic-rich shale were systematically studied using FIB-SEM, mineral contentanalysis, organic geochemical analysis and low-temperature and low-pressure nitrogen adsorption porosity determination, and drilling data of typical wells in the Dangyang synclinorium. (1) Vertically, shale reservoirs from the Wufeng Formation(O3w) are quite different from the first section of the first member of Longmaxi Formation (S1l11). High-quality shale reservoirs are developed from S1l11(1) to S1l11(2) sublayers, with a high abundance of organic matter (2.45%-6.98%), type Ⅱ1-Ⅱ2 organic matter, rather high thermal evolution degree, high brittle mineral content (34.0%-85.5%), low clay mineral content (9.0%-40.3%), and high total gas content (1.76-4.30 m3/t). Organic pores are well developed. In the S1l11(3) sublayer, affected by the intensified Caledonian tectonic activity, terrigenous material input increased, and reservoir quality began to deteriorate. (2) Horizontally, organic-rich shale of the Wufeng-Longmaxi formations in the Dangyang synclinorium become thicker from southeast to northwest, and the reservoir quality becomes better. (3) Shale reservoirs in the S1l11(1)-S1l11(2) sublayers in the study area are the "sweetest" and the "most brittle".However, considering the convenience of real-time monitoring and adjustment of well trajectory during horizontal drilling, the upper and lower half of GR peak in the S1l11(1) sublayer should be selected as the best horizontal target of horizontal wells.
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图 5 中扬子地区当阳复向斜五峰组—龙一1亚段泥页岩储集空间特征
a.有机质表面多孔,充填黄铁矿颗粒间,DY1井,3 499.46 m,五峰组;b.硅质颗粒间充填有机质,有机质表面发育溶蚀孔洞,DY1井,3 495.74 m,龙一11小层;c.黏土矿物层间孔隙常呈薄片状或纤维状,连通性较好,DY1井,3 498.36 m,五峰组;d.黄铁矿粒间孔,有机质充填孔隙内,DY1井,3 499.46 m,龙一11小层;e.白云石颗粒与有机质形成粒缘缝,DY1井,3 497.99 m,龙一11小层;f.磷灰石颗粒内发育溶蚀孔,DY1井,3 495.1 m,龙一12小层;g.石英颗粒内发育少量粒内孔,DY1井,3 499.5 m,五峰组;h.微裂缝,DY1井,3 497.99 m,龙一11小层
Figure 5. Reservoir space characteristics of O3w-S1l11 shale of Dangyang synclinorium
表 1 中扬子地区当阳复向斜五峰组—龙一1亚段页岩样品有机质成熟度、类型及干酪根显微组分
Table 1. Maturity, type and macerals of organic matter of shale samples in O3w-S1l11 of Dangyang synclinorium
井号 样品编号 层位 深度/m EqVRo/% BRo/% 组分含量/% 类型 腐泥组 沥青组 壳质组 镜质组 惰质组 Y101 Y101-1 龙一1亚段4小层 4 061.6 4.05 5.65 62 - - - 38 Ⅱ2 Y101 Y101-10 龙一1亚段4小层 4 071.2 2.68 3.57 65 - - - 35 Ⅱ2 Y101 Y101-16 龙一1亚段3小层 4 077.3 3.01 4.07 58 - - - 42 Ⅱ2 Y101 Y101-26 龙一1亚段2小层 4 087.8 2.73 3.64 52 - - - 48 Ⅱ2 Y101 Y101-33 五峰组 4 095.1 2.82 3.78 51 - - - 49 Ⅱ2 DY1 DY1-3 龙一1亚段1小层 3 497.0 2.96 3.99 76 22 - - 2 Ⅰ DY1 DY1-6 五峰组 3 498.4 3.01 4.07 74 20 - 2 4 Ⅱ1 DY1 DY1-14 五峰组 3 503.0 3.09 4.19 70 23 - 2 5 Ⅱ1 DY2 DY2-5 龙一1亚段4小层 3 958.2 2.30 2.99 60 - - - 40 Ⅱ2 DY2 DY2-7 龙一1亚段4小层 3 962.0 2.54 3.35 58 - - - 42 Ⅱ2 DY2 DY2-11 龙一1亚段3小层 3 973.2 2.40 3.14 55 - - - 45 Ⅱ2 DY2 DY2-13 龙一1亚段2小层 3 980.0 2.46 3.23 54 - - - 46 Ⅱ2 DY2 DY2-15 龙一1亚段1小层 3 982.8 2.30 2.99 60 - - - 40 Ⅱ2 注:沥青反射率(BRo)与镜质体反射率(EqVRo)相关关系:EqVRo=0.656 9BRo+0.336 4 [16]。 表 2 中扬子地区当阳复向斜五峰组—龙一1亚段页岩样品孔隙结构参数
Table 2. Pore structure parameters of O3w-S1l11 shale samples of Dangyang synclinorium
井号 样品编号 层位 深度/m BET比表面积/(m2·g-1) BJH总孔容/(cm3·g-1) t-plot微孔比表面积/(m2·g-1) t-plot微孔孔容/(cm3·g-1) 微孔比表面积比例/% 微孔孔容比例/% 平均孔径/nm DY1 DY1-4 龙一1亚段1小层 3 498.0 36.51 0.012 6 21.04 0.008 5 57.62 67.51 6.15 DY1 DY1-6 五峰组 3 498.4 38.77 0.011 7 22.87 0.009 3 59.00 79.34 5.44 DY1 DY1-8 五峰组 3 502.1 14.25 0.012 9 6.05 0.002 5 42.47 19.39 6.60 DY2 DY2-5 龙一1亚段4小层 3 958.2 5.39 0.020 6 0.68 0.000 3 12.69 1.41 14.96 DY2 DY2-7 龙一1亚段4小层 3 962.0 5.26 0.021 0 0.60 0.000 3 11.46 1.19 15.44 DY2 DY2-11 龙一1亚段3小层 3 973.2 21.84 0.025 2 8.14 0.003 9 37.26 15.54 8.42 DY2 DY2-13 龙一1亚段2小层 3 980.0 18.65 0.021 9 6.20 0.003 0 33.27 13.49 8.22 DY2 DY2-15 龙一1亚段1小层 3 982.8 18.07 0.023 9 6.02 0.002 9 33.32 12.02 9.04 -
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