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.

摘要： 陕北地区上三迭统(延长统)砂体的成岩作用强烈,砂体经历压实、压溶和自生矿物充填等成岩变化后,多数成了低渗透砂体,渗透率一般小于1个毫达西。近期在陕北地区发现了大面积分布的由浊沸石胶结物被溶蚀而成的次生孔隙砂体,渗透率可达3～6毫达西,并已在此类砂体中获得了较高产油量。浊沸石次生孔隙砂体分布于物源来自富含斜长石(岩浆岩、结品片岩母岩)的三角洲平原分流河道相和三角洲前缘相带中。浊沸石次生孔隙砂体具特殊的孔隙结构,渗透率低、含水饱和度高、含油级别低的次生孔隙砂体也往往能产纯油而不产水。

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