Yu Shanshan, Zhao Zhigang, Zhu Yanhe, Zhu Xiaomin, Lai Jin, Li Dan, Wang Xiaolin
CNOOC Research Institute Ltd., Beijing 100028, China.
College of Geosciences, China University of Petroleum, Beijing 102249, China.
ACS Omega. 2024 Apr 10;9(16):18127-18136. doi: 10.1021/acsomega.3c10097. eCollection 2024 Apr 23.
Recently, horizontal well L47-1CH in the Longdong area of the southwestern Ordos Basin made a significant breakthrough in bauxite natural gas exploration, changing the traditional geological understanding that bauxite could not form effective reservoirs. To further explore the exploration and development potential of bauxite natural gas reservoirs in the northeast of the Ordos Basin, it is urgent to carry out basic geological studies. This paper discusses the sedimentary environment, reservoir characteristics, and formation patterns of the bauxite gas reservoirs in the LX Block using trace elements, thin sections, X-ray diffraction, scanning electron microscopy, conventional physical properties, constant pressure mercury, etc. Then, the distribution pattern of bauxite was studied according to the restoration of the karst paleogeomorphology, and the formation model of bauxite was ultimately established. The results show that bauxite developed a clear triple-segment structure vertically, characterized by rich iron at the bottom, high aluminum at the middle, and low iron at the top. The mineral composition of the bauxite section mainly includes diaspore, iron minerals, titanium minerals, and birnessite. The types of pores mainly include intra- and intergranular dissolved pores, matrix-dissolved pores, intercrystalline pores, and microfractures. The porosity ranges from 1.51 to 9.90%, with a relatively good sorting and connectivity of the pore and throat. The bauxite was formed in a hot and humid climate, deposited in a shallow-water tidal flat and lagoon sedimentary environment with oxygen depleted, and experienced oscillatory regression during the deposition process. The thickness of bauxite is significantly controlled by karst paleogeomorphology, and it is mainly distributed at the negative terrain positions of karat pits and karst terraces. The above results can provide a geological basis for the exploration and development of bauxite in the Ordos Basin and similar basins worldwide.
最近，鄂尔多斯盆地西南部陇东地区的水平井L47-1CH在铝土矿天然气勘探方面取得重大突破，改变了铝土矿无法形成有效储层的传统地质认识。为进一步探究鄂尔多斯盆地东北部铝土矿天然气藏的勘探开发潜力，开展基础地质研究迫在眉睫。本文利用微量元素、薄片、X射线衍射、扫描电子显微镜、常规物性、恒压压汞等方法，探讨了LX区块铝土矿气藏的沉积环境、储层特征及成矿模式。然后，根据岩溶古地貌恢复研究了铝土矿的分布规律，最终建立了铝土矿成矿模式。结果表明，铝土矿在垂向上发育明显的三段式结构，底部富铁，中部高铝，顶部贫铁。铝土矿剖面矿物成分主要包括一水硬铝石、铁矿物、钛矿物和水钠锰矿。孔隙类型主要包括粒内和粒间溶蚀孔、基质溶蚀孔、晶间孔和微裂缝。孔隙度为1.51%~9.90%，孔喉分选性和连通性较好。铝土矿形成于湿热气候条件下，沉积于缺氧的浅水潮坪和泻湖沉积环境，沉积过程中经历了振荡海退。铝土矿厚度受岩溶古地貌显著控制，主要分布于岩溶坑和岩溶阶地的负地形部位。上述成果可为鄂尔多斯盆地及全球类似盆地铝土矿的勘探开发提供地质依据。
