Gas-bearing characteristics and preservation conditions of Upper Ordovician Wufeng-Lower Silurian Longmaxi shale in western Hubei
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摘要: 上奥陶统五峰组—下志留统龙马溪组为鄂西地区重要的页岩气勘探目的层。利用鄂西地区20多口调查井资料,对其五峰组—龙马溪组岩性、沉积相、含气性特征及保存条件进行了分析。五峰组以黑色含碳硅质页岩为主,为深水硅泥质陆棚相,龙马溪组以灰黑色碳质页岩为主,为深水泥质陆棚相;五峰组—龙马溪组与下志留统新滩组下部组成2个三级层序且含气量符合TST1 > TST2 > HST2 > HST1的特征,五峰组含气性略好于龙马溪组,天阳坪断裂以北及咸丰断裂带以东含气量好,由于多数钻井处于深水陆棚相,沉积相对含气性的平面差异影响较小;目的层顶板下志留统新滩组粉砂质泥岩和底板奥陶系致密灰岩横向分布稳定,为区域良好盖层;五峰组—龙马溪组埋藏史可以划分为4个阶段,与四川盆地相比鄂西地区的埋藏史呈现“抬升时间偏早”和“抬升速率过快”的特征。埋深、距离正断层的远近对含气性有一定影响,但断裂和褶皱的匹配样式是影响含气量高低的最关键因素,远离正断层且位于向斜核部或翼部,离正断层较远、位于断层下盘且上倾方向未与断裂沟通这2种构造样式有利于页岩气的聚集成藏。Abstract: The Upper Ordovician Wufeng to Lower Silurian Longmaxi formations are important exploration targets for shale gas in the western Hubei province. The lithology, sedimentary facies, gas-bearing characteristics and preservation conditions of the Wufeng-Longmaxi formations were analyzed with the samples of more than 20 survey wells. The Wufeng Formation is dominated by black carbonaceous siliceous shale of deep-water siliceous argillaceous shelf facies, while the Longmaxi Formation is dominated by gray-black carbonaceous shale of deep-water argillaceous shelf facies. The Wufeng-Longmaxi formations and the lower part of Lower Silurian Xintan Formation consist of two three-level sequences, and the gas content conforms to the characteristics of TST1 > TST2 > HST2 > HST1. The gas content of the Wufeng Formation is slightly higher than that of the Longmaxi Formation. A good gas potential has been found to the north of Tianyangping Fault and the east of Xianfeng Fault. Since most wells were in the deep shelf facies area, sedimentary facies have little effect on the plane distribution of shale gas content. The studies of preservation conditions showed that both the Xintan Formation as the roof and the Ordovician as the floor have good sealing properties. The burial history of Wufeng-Longmaxi formations can be divided into four stages, and shows the characteristics of "early uplift time" and "rapid uplift rate" when compared with the Sichuan Basin. The burial depth and the distance to normal fault have certain influence on the gas content. However, the matching pattern between fault and fold is the most important factor affecting gas content. Two structural patterns are beneficial to shale gas accumulation, one is being far away from normal fault and locating at the syncline wing or core, the other is being far away from normal fault and locating at the footwall of fault and the target stratum is not connected to the fault in the up-dip direction.
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Key words:
- preservation condition /
- shale gas /
- gas content /
- Wufeng-Longmaxi formations /
- western Hubei
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表 1 鄂西地区主要区域断裂带特征
Table 1. Characteristics of main regional fault zones in western Hubei province
名称 性质 走向 倾向 倾角/(°) 长度/km 切穿层位 齐岳山断裂(F1) 压扭性 北北东 北西 80 50 建始—彭水断裂(F2) 早期压扭、后期张性 北北东 南东 310 恩施—黔江断裂(F3) 张性断裂 北北东 南东 60~80 120 三叠系—志留系 大青山断裂(F4) 早期张性、晚期压扭性 北北东 东 160 三叠系—志留系 咸丰断裂(F5) 早期为压扭性、后期张性 北北东 北西 50 80 襄广断裂(F6) 早期逆冲、中期断陷、后期逆冲推覆 北东东 北 25~75 300 阳日断裂(F7) 逆冲断层 东西 北 30~80 120 志留系—震旦系 新华断裂(F8) 早期压剪性,后期张性 北北东 西 360 侏罗系—震旦系 仙女山断裂(F9) 早期张性、中期压扭性、后期张性 北北西 南西 100 白垩系—二叠系 天阳坪断裂(F10) 逆冲断层 北西 南西 20~40 150 寒武系—震旦系 雾渡河断裂(F11) 早期压性、后期张性 北西 北 60~80 160 寒武系—震旦系 通城河断裂(F12) 张性断裂 北北西 东 200 三叠系—寒武系 远安断裂(F13) 早期压扭性、中期张性、后期压扭性 北北西 西 50~80 60 志留系—震旦系 表 2 鄂西地区上奥陶统五峰组—下志留统龙马溪组含气性特征统计
Table 2. Characteristics of gas content of Wufeng-Longmaxi formations in western Hubei province
井号 底界埋深/m 厚度/
mω(TOC)/% 沉积相带 构造部位 与正断层距离/
km解吸含气量/
(m3·t-1)总含气量/
(m3·t-1)咸地2 1 520.0 73.1 0.65~8.08$\frac{0.65 \sim 8.08}{1.95}$1.95 深水陆棚 中央背斜带桑柘坪向斜近核部 距恩施—黔江断裂
12.5$\frac{0.15 \sim 1.75}{0.62}$ $\frac{0.63 \sim 3.45}{1.56}$ 来地1 947.9 50.9 深水陆棚 咸丰背斜带内次级向斜近核部 距新华断裂
13.9$\frac{0.80 \sim 3.73}{1.67}$ ZY1 261.5 35.9 $\frac{0.26 \sim 4.71}{1.55}$ 深水陆棚 咸丰背斜带次级向斜近核部 距新华断裂
1.9$\frac{0.30 \sim 0.50}{0.40}$ ZY2 378.4 35.4 $\frac{0.20 \sim 7.60}{1.88}$ 深水陆棚 咸丰背斜带次级向斜近核部 距新华断裂
1.4$\frac{0.22 \sim 0.39}{0.34}$ $\frac{1.37 \sim 2.13}{1.68}$ WD1 422.0 31.2 $\frac{1.10 \sim 5.00}{3.17}$ 深水陆棚 中央背斜带西翼 距建始—彭水断裂
5.6$\frac{0.20 \sim 1.40}{0.63}$ 茅地1 899.4 51.6 $\frac{0.99 \sim 6.20}{3.42}$ 深水陆棚 中央背斜带东翼 距建始—彭水断裂
3.7$\frac{0.04 \sim 0.09}{0.07}$ $\frac{0.18 \sim 0.47}{0.35}$ 建地1 1 780.0 42.0 $\frac{0.20 \sim 10.50}{4.39}$ 深水陆棚 花果坪向斜西翼次级背斜东翼 距新华断裂
13.6$\frac{0.11 \sim 0.92}{0.53}$ ZD2 921.5 38.8 $\frac{0.36 \sim 7.76}{1.86}$ 深水陆棚 香龙山背斜北翼 距新华断裂
4.7$\frac{0 \sim 0.12}{0.03}$ $\frac{0 \sim 0.19}{0.04}$ ZD1 346.0 38.8 $\frac{0.54 \sim 4.58}{1.52}$ 深水陆棚 香龙山背斜北翼 距新华断裂
2.20 秭地3 1 162.4 42.5 $\frac{0.08 \sim 5.40}{2.34}$ 深水陆棚 黄陵背斜带次级褶皱背斜东翼 距仙女山断裂
11.8$\frac{0.50 \sim 1.09}{0.73}$ $\frac{1.04 \sim 1.73}{1.31}$ 红地1 496.3 44.5 $\frac{0.23 \sim 5.04}{2.31}$ 深水陆棚 神农架背斜北翼 WD6 245.0 24.5 $\frac{0.90 \sim 4.50}{2.11}$ 深水陆棚 黄陵背斜带西翼 距仙女山断裂
1.7$\frac{0.30 \sim 1.16}{0.36}$ 远地1 786.0 30.0 $\frac{0.43 \sim 4.25}{1.73}$ 深水陆棚 黄陵背斜东翼 距通城河断裂
2.9$\frac{0.13 \sim 1.19}{0.62}$ $\frac{0.32 \sim 1.94}{1.03}$ 宜地1 1 341.0 25.0 $\frac{0.80 \sim 6.00}{3.32}$ 深水陆棚 黄陵背斜东翼 距通城河断裂
7.1$\frac{0.50 \sim 2.16}{0.80}$ 夷地1 625.0 26.1 $\frac{0.24 \sim 5.53}{1.79}$ 深水陆棚 黄陵背斜东翼 距通城河断裂
16.8$\frac{0.52 \sim 2.82}{1.29}$ $\frac{0.57 \sim 3.31}{1.65}$ 宜页2 2 731.0 45.0 $\frac{1.07 \sim 4.30}{2.56}$ 深水陆棚 黄陵背斜东翼 距通城河断裂
12.9$\frac{1.03 \sim 3.33}{1.97}$ WD2 317.9 22.9 $\frac{1.31 \sim 4.89}{2.99}$ 深水陆棚斜坡 香龙山背斜西翼 距新华断裂
2.8$\frac{0.10 \sim 0.30}{0.20}$ $\frac{1.20 \sim 1.55}{1.38}$ 巴地2 1 420.0 23.8 $\frac{0.06 \sim 4.34}{1.86}$ 深水陆棚斜坡 香龙山背斜南东翼 距新华断裂
2.10 长地2 584.6 14.0 $\frac{0.56 \sim 2.28}{1.63}$ 浅水陆棚 宜都—鹤峰背斜带次级向斜北翼 $\frac{0.05 \sim 0.11}{0.07}$ $\frac{0.21 \sim 0.46}{0.28}$ 注:式中分式的意义为:$\frac{\text { 最小值~ 最大值}}{\text { 平均值}}$。 -
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