关键词: 浊沸石, 次生孔隙, 砂体分布, 陕北地区, 延长统, 成岩作用, 渗透率, 斜长石, 油气关系, 三角洲平原分流河道

Abstract: As a result of strong diagenetic process with alterations tnrougn compaction and infilling of authigenic minerals, most of the sand bodies of late Triassic age in northern Shaanxi have low permeability of less than l and in general. Recently, it has been discovered that through dissolution of lomonitic cements, sand bodies with secondary porosity and permeability of 3-5md are extensively distributed there, and oil of appreciable amount has been obtained, These sand bodies are distributed in the delta-plain distributary facies and delta-front facies zones with abundant anorthose(magmatic rock, mother rock of crystalline schist). They have a special porosity structure, low permeability and high water saturation Sand bodies with secondary porosity may yield clean oil in small amount without any water. The temperature for forming lomonites in the sand bodies of Yanchang series is 50-80℃; they are formed before the primary migration of oil and gas, the paper concludes.