同沉积期火山作用对鄂尔多斯盆地上古生界砂岩储层形成的意义

鄂尔多斯盆地上古生界主要为一套陆源碎屑沉积体系，其中广泛发育河流-三角洲相砂岩储集体，是该区上古生界天然气聚集成藏的主要场所。但由于陆源杂基的充填以及成岩压实作用、胶结作用的改造，大部分砂层储集性能都较差而无工业性储集意义。本文通过对鄂尔多斯盆地上古生界砂岩储层孔隙成因的分析，提出在局部层段集中分布的孔隙性砂岩，其孔隙主要为次生溶蚀成因。进一步的研究表明，由同沉积期火山作用形成的、分布于砂岩层中的火山碎屑组分的成岩溶蚀是次生溶孔形成的主要原因。因此，同沉积期火山作用控制了该区上古生界主要砂岩储层的发育和分布。中基性火山作用由于能提供较多的“易溶组分”，从而控制了次生溶孔发育的较高渗透性砂岩储层的分布； 而影响更为广泛的酸性火山作用则主要形成以蚀变高岭石晶间孔为主的低渗透性储层。

Significance of synsedimentary volcanism for formation of sandstone reservoirs of the Upper Paleozoic in Ordos Basin

The Upper Paleozoic in the Ordos Basin is mainly made up of a terrigenous clastic sedi- mentary system.The fluvial-delta facies sandstone reservoirs are widespread and they constitute the main places for the Upper Paleozoic gas accumulation in this area. Owing to the terrigenous matrix filling,dia- genetic compaction and cementation,however,most of the primary intergranular pores of the sandstones had been filled up.Therefore,most of the sandstones become too tight to make up effective reservoirs. Through the genetic analyses of the pores of the Upper Paleozoic sandstone reservoirs in the Ordos Basin,it can be suggested that the porous sandstones which are concentrated in parts of the layers,are dominated by the secondary dissolution pores. Further studies show that the secondary dissolution pores were mainly caused by the genetic solution of the pyroclastic components,which had derived from the synsedimentary volcanism and were distributed in the sandstone formations.Therefore,the synsedimentary volcanism con- trolls the development and distribution of the main Upper Paleozoic sandstone reservoirs of this area.Owing to the easily-dissolved component supplied by the intermediate to basic volcanism,it controlls the distribu- tion of porous sandstone reservoirs with higher permeability,while the acid volcanism mainly forms the low permeable sandstone reservoirs,which are dominated by the kaolinite intercrystal pores.