煤系地层中砂岩火山尘填隙物的成岩作用特征——以鄂尔多斯盆地天然气储层为例

The formation and evolution of volcanic dust fillings of sandstone in coal measures strata of Ordos Basin

在晚石炭世—早二叠世,鄂尔多斯盆地泥炭沼泽环境下发育的富含火山尘填隙物砂岩是煤成气的主要储集层。研究表明,该类砂岩的原杂基主要由同沉积期初步水化作用的火山尘构成;在煤系地层水环境下,火山尘经过初步水化作用后并不能形成沸石族矿物,主要形成了铝硅酸盐和硅酸盐的微细混合物;在埋藏过程中,砂岩火山尘填隙物的水岩反应受到煤系地层水介质性质及其活动性影响,主要发生脱水收缩作用、溶解作用、蚀变作用、碳酸盐交代作用和重结晶作用;火山尘填隙物的成岩作用在局部范围内可改善天然气储层,但也增强了储层的非均质性。

During the period of Late Carboniferous and Early Permian, the sandstone with abundant volcanic dust fillings was mainly deposited in a peat marsh environment, which constituted a favorable reservoir of coal-formed gas in Ordos Basin. Studies show that the original fillings of sandstone are mainly superficially hydrolyzed volcanic dust, which is a superfine mixture of aluminosilicate and silicate. It is difficult for volcanic dust to form zeolite during hydrolyzing under the condition of acidic syngenetic water in a peat marsh environment. The tuff fillings of sandstone are susceptible to the property and activity of the formation water, and have mainly experienced synaeresis, dissolution, alteration, carbonate metasomatism and recrystallization in a burial environment. The evolution of tuff fillings of sandstone can improve the quality of reservoir locally, but enhance the heterogeneity of reservoir regionally.