鄂尔多斯盆地西缘前陆盆地中生界成岩作用研究

鄂尔多斯西缘前陆盆地中生界储层砂岩成岩作用主要受前陆盆地构造演化的影响,不同构造区带砂岩储层的成岩环境存在一定的差别。研究发现,冲断带近物源区由于杂基和软矿物含量高,压实作用表现较为强烈,砂岩物性较差;但斜坡带远离物源区压实程度较弱,原生粒间孔隙发育。前陆盆地不同区带的构造演化强度不同,形成了不同的成岩强度,冲断带的Ro值为0.5%～0.65%,其成岩演化刚进入晚成岩A期,但成岩演化程度比斜坡带略高,而坳陷带经历的成岩演化最高,成岩演化程度相对较高(Ro:0.7%～0.9%),强度最大。坳陷带比冲断带、斜坡带含有更高含量的富铁方解石,这些铁方解石属于成岩晚期的产物,很难遭受后期溶蚀改造,所以坳陷带中铁方解石含量较高的地区储层物性也比较差,其机理可能与黏土矿物转化和长石类矿物发生溶蚀有关。

The Research on the Diagenesis on Mesozoic in Foreland Basin of the Western Margin in Ordos Basin

The reservoir sandstone in mesozoic in foreland basin in the western margin of the Ordos basin,effected mainly by the foreland basin structure evolution,the different reservoir of belts experienced different diagenesis environment.The research discovered that,the thrust belt near source area,with high content soft debris and matrix,induced strong compaction and bad reservoir quality.But the slope belt is far away the source area,with weak compaction and dissolution,and the primary porosity is developed.The structure evolution of the foreland basin in western margin created the different diagenesis degree:the Ro value of thrust belt is 0.5%~0.6%,belonged to the A term in late diagenesis stage,and its diagenetic evolution is higher than slope belt.The depression belt suffered the most strong diagenesis stage,the Ro value is 0.70%~0.9%.The depression belt has the highest ferro-calcite content than the trust belt and slope belt,these ferro-calcites belong to the later diagenesis stage,so with weak dissolution,resulted the bad reservoir quality.The ferro-calcite cementation possibly formed associated with the transformation of clay mineral and the dissolution of feldspar.