陇东太原组铝土岩分布特征及成藏主控因素

Distribution characteristics and main controlling factors of accumulation of bauxite rock in Taiyuan Formation in Longdong area

近期,太原组铝土岩气藏已经成为鄂尔多斯盆地陇东地区的勘探热点。为系统探究铝土岩分布及成藏主控因素,基于最新钻井岩心、岩石薄片、三维地震、测井、扫描电镜、模型正演等方法,详细研究了太原组铝土岩分布特征,进而阐述了铝土岩成藏主控因素。研究结果表明,含铝岩系纵向具有典型的五段式,其中C段是铝土岩的主要储集层段,硬水铝石含量超过80%。含铝岩系纵向岩性组合主要受岩溶古地貌单元控制,铝土岩在岩溶高地、岩溶斜坡及岩溶洼地分别呈点状、带状及片状分布特征,其中岩溶斜坡区铝土岩储层最为发育。铝土岩天然气富集主要受优质储层、断裂、裂缝及构造位置综合控制,其中储层是天然气富集高产的前提,早期断裂表现出建设作用,晚期断裂表现出破坏作用,裂缝能够改善储层物性,构造高部位的低幅度构造或鼻状圈闭更易成藏,岩溶斜坡区是最有利于铝土岩天然气成藏的古地貌单元。

Recently,the bauxite gas reservoir of Taiyuan Formation has become a hot spot of exploration in Longdong area of Ordos Basin.In order to systematically explore the distribution of bauxite rock and the main controlling factors of reservoir formation,based on the latest drilling cores,rock slices,three-dimensional seismic,logging,scanning electron microscopy,model forward modeling and other methods,the distribution characteristics of bauxite rock in Taiyuan Formation were studied in detail,and then the main controlling factors of bauxite rock reservoir formation were expounded.The results show that the aluminiferous rock series has a typical five-stage type in the longitudinal direction,in which the C section is the main reservoir section of the bauxite rock,and the content of diaspore is more than 80%.The longitudinal lithologic association of the aluminiferous rock series is mainly controlled by the karst paleogeomorphology unit.The distribution characteristics of bauxite in karst highland,karst slope and karst depression are punctate,banded and flaky,respectively.The bauxite reservoir in the karst slope area is the most developed.The enrichment of natural gas in bauxite rock is mainly controlled by high-quality reservoirs,faults,fractures and structural positions.Reservoirs are the premise of natural gas enrichment and high yield.Early faults show construction effect,and late faults show destruction effect.Fractures can improve reservoir physical properties.Low-amplitude structures or nose-like traps in high structural parts are more likely to accumulate.Karst slope area is the most favorable paleogeomorphologic unit for natural gas accumulation in bauxite rock.