Reservoir characteristics and development control factors of Benxi Formation bauxite in the Linxing area of Ordos Basin
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摘要:
近年来,鄂尔多斯盆地陇东地区太原组铝土岩气勘探取得了重大突破,吸引了国内外的广泛关注。同期,临兴地区本溪组铝土岩气也取得了一定进展,但对于该区铝土岩储层特征及其发育控制因素认识不清,制约了勘探进程。为了明确临兴地区本溪组铝土岩的储层特征与控制因素,通过开展全岩 X 射线衍射(X-ray diffraction,简称 XRD)、铸体薄片、扫描电镜、高压压汞、氮气吸附、二氧化碳吸附、常规孔渗检测等分析手段,对铝土岩储层的矿物组成、孔隙结构、储层物性等进行了精细表征,并结合地震测井等资料对铝土岩储层发育的控制因素进行了探讨。研究表明:临兴地区本溪组铝土岩中含铝矿物主要为硬水铝石,孔隙类型主要为粒内溶孔、粒间溶孔、基质溶孔、晶间孔以及微裂隙,偶见有机质孔。此外,铝土岩孔隙体积主要由介孔和宏孔提供,孔峰分布范围主要为30~70,80~130,
4000 ~13000 nm。再次,铝土岩储层物性条件一般,孔隙度平均为3.28%,渗透率平均为1.398×10−3 μm2,但底部硬水铝石含量较高层段仍具有较好的物性条件。最后,临兴地区铝土岩储层发育受控于古地貌形态、古沉积环境和成岩作用,其中,洼地和沟槽的古地貌形态和封闭−半封闭的间歇沼泽和泻湖沉积环境控制了铝土岩的富集和分布,成岩作用则是在沉积环境基础上控制了铝土岩储层储集空间类型和物性条件。研究成果可为铝土岩气勘探提供理论参考。Abstract:In recent years, the bauxite gas exploration of the Taiyuan Formation in the Longdong area of Ordos Basin has made a breakthrough, which has attracted wide attention at home and abroad. During the same period, the bauxite rock gas of the Benxi Formation in the Linxing area has also made some progress; however, the characteristics and controlling factors of the bauxite reservoir in this area remain unclear, which restricts the exploration process.
Objective To identify the reservoir characteristics and influencing factors of Benxi Formation bauxite in the Linxing area,
Methods the paper carried out X-ray diffraction (XRD), cast sheet imaging, scanning electron microscope-energy-dispersive spectrometer (SEM-EDS), mercury intrusion porosimetry, nitrogen and carbon dioxide adsorption, and routine porosity measurements, coupled with seismic logging data, to characterize the mineral composition, pore structure, and physical properties of the bauxite reservoir and to discuss the controls on its development.
Result The results show that the aluminum-bearing minerals in Benxi Formation bauxite in the Linxing area are dominated by diaspore. Pore types are primarily intra-granular, intergranular, matrix, and microcrack pores, with occasional organic pores. Pore volume is mainly contributed by mesopores and macropores, with pore-size peaks mainly at 30−70, 80−130,
4000 −13000 nm. The overall reservoir physical properties are modest, with an average porosity of 3.28% and an average permeability of 1.398×10−3 μm2. However, the lower part of the section, which has a higher diaspore content, exhibits relatively better properties. Finally, the development of the Linxing bauxite reservoir is controlled by palaeo-geomorphology, palaeo-sedimentary environment, and diagenesis. Specifically, accumulation and distribution of bauxite are controlled by the paleogeomorphology of depressions and troughs and by enclosed to semi-enclosed intermittent swamps and lagoons. Diagenesis determines the reservoir-space types and the resulting physical-property conditions within the sedimentary context.Conclusion The research results can provide theoretical guidance for the bauxite gas exploration.
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图 1 鄂尔多斯盆地临兴地区地质综合图
a. 鄂尔多斯盆地构造单元及临兴地区位置,据文献[12]修改;b. 临兴地区A井柱状图。GR. 自然伽马;CNCF. 补偿中子;ZDEN. 密度;M2RX. 高分辨感应电阻率;下同
Figure 1. Geological comprehensive map of Linxing area, Ordos Basin
图 3 临兴地区A井本溪组铝土岩孔隙特征
a.
1996.43 m,碎屑矿物溶蚀孔被黏土矿物充填;b.2003.15 m,硬水铝石粒间溶孔;c.2003.15 m,粒间孔内充填硬水铝石和黏土矿物等;d.2003.15 m,硬水铝石晶间孔和微裂隙;e.1999.85 m,黄铁矿晶间孔和有机质孔;f.2002.31 m,黏土矿物晶间孔;g.2000.07 m,有机质孔;h.2000.07 m,金红石微孔隙以及微裂隙Figure 3. Pore characteristics in Benxi Formation bauxite rock of Well A in the Linxing area
图 9 临兴地区铝土岩成岩作用阶段(据文献[33]修改;Ro. 镜质体反射率;S. 蒙脱石)
Figure 9. Diagenetic stage of bauxite rock in the Linxing area
表 1 临兴地区本溪组铝土岩XRD分析结果
Table 1. XRD analysis results of Benxi Formation bauxite rock in the Linxing area
取心井 样品编号 深度/m 石英 钛质矿物 铁质矿物 黏土矿物 铝质矿物 伊/蒙混层比(I/S) 锐钛矿 金红石 黄铁矿 赤铁矿 高岭石 伊利石 伊蒙混层 硬水铝石 wB/% A 1 1992.82 16.99 / / / / 40.13 9.33 / 33.55 / 2 1993.86 27.64 / / 5.76 / 29.58 / / 37.02 / 3 1995.09 / 2.40 / / 29.73 34.14 4.21 / 29.52 / 4 1996.43 / 3.69 / / 2.12 21.78 / 44.25 28.16 80%∶20% 5 1998.73 3.65 2.81 / / 1.21 26.54 / 26.95 38.84 80%∶20% 6 1999.85 / 14.71 / 1.68 / 37.26 1.24 / 45.11 / 7 2000.07 0.97 2.31 0.1 / 0.80 28.84 / 28.85 38.13 80%∶20% 8 2002.31 2.44 / / / 4.90 41.63 6.17 / 44.86 / 9 2002.97 / 7.11 0.1 / 4.81 45.91 4.73 / 37.34 / 10 2003.15 / / 0.1 14.34 / 10.18 / / 75.38 / B 11 2054.80 2.9 2.82 / / 3.14 53.97 / 21.70 15.47 80%∶20% 12 2059.20 2.14 4.89 / / 1.68 55.50 / / 35.79 / 13 2065.80 / 5.70 / / / 20.87 / / 73.43 / C 14 2343.30 3.39 4.23 / / 1.28 71.35 / / 19.75 / 15 2348.20 / 3.12 / / / 62.51 3.13 / 31.24 / 16 2350.80 / / / / 17.32 34.70 / / 47.98 / 平均 / 3.76 3.36 0.02 1.36 4.19 35.43 4.80 7.61 39.47 80%∶20% 表 2 临兴地区A井本溪组铝土岩储层低温气体吸附与高压压汞实验孔隙参数
Table 2. Pore parameters from low-temperature gas adsorption and mercury intrusion porosimetry experiments in Benxi Formation bauxite reservoir of Well A in the Linxing area
样品编号 深度/m CO2 吸附 N2 吸附 高压压汞 孔隙体积/(cm3·g−1) 比表面积/(m2·g−1) 孔径/nm 孔隙体积/(cm3·g−1) 比表面积/(m2·g−1) 孔径/nm 孔隙体积/(cm3·g−1) 比表面积/(m2·g−1) 孔径/nm 1 1992.82 0.021 25.372 0.472 0.135 38.748 12.529 0.0033 0.359 37.12 2 1993.86 0.020 25.227 0.472 0.128 35.721 12.897 0.0027 0.248 43.46 3 1995.09 0.013 15.509 0.507 0.090 20.558 14.805 / / 246.60 4 1996.43 0.018 23.122 0.489 0.125 32.730 13.549 0.0028 0.046 22.62 5 1998.73 0.022 29.597 0.472 0.143 39.550 12.751 0.0029 0.509 / 6 1999.85 0.018 20.420 0.489 0.104 25.375 14.185 0.0001 0.0001 188.60 7 2000.07 0.020 23.533 0.489 0.136 35.632 13.733 0.0010 0.021 354.29 8 2002.31 0.018 20.689 0.489 0.120 31.425 13.845 0.0002 0.003 429.94 9 2002.97 0.017 21.706 0.489 0.121 30.053 14.332 0.0007 0.006 14.56 10 2003.15 0.011 11.802 0.507 0.062 14.416 15.607 0.0035 0.955 37.12 平均 / 0.018 21.698 0.488 0.116 30.421 13.966 0.0019 0.239 246.85 表 3 临兴地区A井本溪组铝土岩储层物性参数
Table 3. Reservoir physical properties of Benxi Formation bauxite rock of Well A in the Linxing area
样品编号 深度/m 孔隙度/% 渗透率/10−3μm2 1 1992.82 1.7 1.212 2 1993.86 1.5 0.494 3 1995.09 2.6 0.922 4 1996.43 0.5 0.203 5 1998.73 3.45 0.604 6 1999.85 4.1 1.924 7 2000.07 0.9 0.128 8 2002.31 5.5 2.224 9 2002.97 2.6 1.853 10 2003.15 9.9 4.418 平均 / 3.28 1.398 陇东地区[8] / 10.65 4.040 -
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