山西太原地区晚石炭世-早二叠世海平面升降对煤储集层非均质性的控制作用

Control of Late Carboniferous-Early Permian sea level fluctuation on coal reservoir heterogeneity,Taiyuan, Shanxi

根据山西太原地区晚石炭世-早二叠世海平面变化特征,分析、讨论海平面升降对该区上石炭统、下二叠统煤储集层非均质性的控制作用。海平面相对快速上升期间(海侵体系域)形成的煤层少且薄,分布范围小,多呈透镜状,横向连通性差,平面非均质性强,但夹矸层少、煤层灰分产率一般较低,因此层内非均质性弱。海平面相对下降期(高位体系域),尤其是晚期(高位体系域晚期),形成的煤层多且厚,分布范围广,横向连通性好,平面非均质性弱,但夹矸层较多、煤层灰分产率一般较高,层内非均质性较强。因此,海平面升降对煤储集层平面非均质性的控制作用主要表现在控制煤储集层形态以及横向连续性和连通性;对层内非均质性的控制作用主要表现在控制煤矸石夹层数和灰分产率;对层间非均质性的控制作用主要表现在控制煤储集层灰分产率、煤岩显微组分。在海陆交互相地层中,由于海平面升降引起煤层特征的变化,导致层间非均质性较强。

Sea level fluctuation can control both the types of sedimentary environments and types and scales of swamps. Sea level fluctuation is closely related with abundance of coal, coal thickness, coal lateral stability, coal composition, coal ash production rate, coal gangue distribution, etc. As these parameters can influence porosity and permeability of coal beds, sea level fluctuation directly or indirectly controls porosity development and heterogeneity of coal beds. The study on coals of the upper Carboniferous and Lower Permian in Taiyuan, Shanxi Province, shows that during rapid rise of sea level (transgressive system tract), the coal beds formed are few and thin. They are mostly lenticular in shape and unstable laterally, and thus their lateral heterogeneity is strong. But their gangue beds are less, ash production rate is low, and intrabed heterogeneity is weak. During relative fall of sea level (high-stand system tract) , the coal beds formed are many and thick, which are mostly sheet-shaped and stable laterally, and thus their lateral heterogeneity is weak. But their gangue beds are many, ash production rate is high, and intrabed heterogeneity is strong. In interbedded marine-nonmarine strata, frequent fluctuation of sea level results in frequent change of coal bed characteristics, and thus interbed heterogeneity is strong.