Reservoir characteristics and development control factors of Benxi Formation bauxite in 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。【目的】为了明确临兴地区本溪组铝土岩的储层特征与控制因素,【方法】本文通过开展全岩XRD衍射、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探讨。【结论】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、晶间孔隙以及微裂隙,偶见有机质孔隙。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 nm、80-130 nm以及4-13 μm。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。Abstract: In recent years, the bauxite gas exploration of Taiyuan Formation in Longdong area of Ordos Basin has made a major breakthrough, which has attracted wide attention at home and abroad. In the same period, the bauxite rock gas of Benxi Formation in Linxing area has also made some progress, but the characteristics and controlling factors of bauxite reservoir in this area are unclear, which restrict the exploration process. [Objective]In order to identify the reservoir characteristics and control factors of Benxi Formation bauxite in Linxing area, [Methods]The paper carried out XRD, casting sheet image, SEM-EDS, mercury intrusion porosimetry, nitrogen adsorption, carbon dioxide adsorption, routine porosity detection and other analysis methods. The mineral composition, pore structure and physical properties of the bauxite reservoir are characterized, and the controlling factors of the development of the bauxite reservoir are discussed based on seismic logging data. [Conclusion]The results show that the aluminum-bearing minerals in the bauxite of Benxi Formation in Linxing area are mainly diaspore, and the pore types are mainly intra granular pores, intergranular pores, matrix pores, intergranular pores and micro-cracks, and occasionally organic pores. In addition, the pore volume of bauxite rocks is mainly provided by mesoporous and macroporous pores, and the distribution range of pore peaks is mainly 30-70 nm, 80-130 nm and 4-13 μm. Thirdly, the physical property conditions of the bauxite reservoir are general, with an average porosity of 3.28% and an average permeability of 1.398×10-3 μm2, but the upper section with higher content of diaspore at the bottom still has better physical property conditions. Finally, the development of bauxite reservoir in Linxing area is controlled by palaeo-geomorphology, palaeo-sedimentary environment and diagenesis. Among them, The accumulation and distribution of bauxite are controlled by the paleogeomorphology of depressions and troughs and the enclosed and semi-enclosed intermittent swamps and lagoons sedimentary environment, while diagenesis controls the reservoir space type and physical property conditions of bauxite reservoirs based on the sedimentary environment.
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