成岩作用对致密油储层分布的影响——以松南让字井斜坡带扶余油层为例

Influence of Diagenesis on the Distribution of Tight Oil Reservoirs:A case study of the Fuyu reservoir,Rangzijing slope zone,southern Songliao Basin

扶余油层是松辽盆地南部最主要的含油层系,目前已进入致密油勘探阶段,查明成岩作用对致密油储层形成和分布规律的影响,对致密油勘探有着至关重要的作用。以松南让字井斜坡带泉四段扶余油层为例,通过岩石薄片、黏土矿物X衍射、扫描电镜实验分析及物性、高压压汞等实验资料,开展成岩作用对致密油储层分布规律的影响研究。研究表明,研究区扶余油层溶蚀孔隙发育的有效储层多为三角洲水下分流河道、分流河道砂岩。在埋藏深度1 750~2 250 m,I/S混层比为25%~15%,对应的成岩阶段为中成岩A2期,此深度带为次生溶蚀孔隙发育带,目前致密油开采多在本带;当埋藏深度大于2 250 m时,I/S混层比小于15%,对应的成岩阶段为中成岩B期,储层进一步致密。将研究区扶余油层划分为常规储层及Ⅰ类致密油储层、Ⅱ类致密油储层与Ⅲ类致密油储层,在纵向上,随埋藏深度的增加,各类储层依次出现。研究区扶余油层致密油勘探最有利的是Ⅰ类和Ⅱ类致密油储层,最有利的勘探深度介于1 750~2 250 m。

The Fuyu reservoir in the Fourth member of the Quantou Formation is the most important oil-bearing reser⁃voir in the southern Songliao Basin,and is currently being explored for tight oil resources.The diagenesis is highly in⁃fluential in the formation and distribution of tight oil reservoirs.The Fuyu reservoir,located in the Rangzijing slope zone,was studied to determine the influence of diagenesis on the distribution of tight oil reservoirs using the methods of thin sections,clay mineral XRD,SEM observations,physical properties,high-pressure Hg injection and other ex⁃perimental techniques.These showed that most of the effective reservoirs with dissolution pores in the study area com⁃prise deltaic underwater distributary channels and resulting sandstone.At depths of 1750⁃2250 m,the mudstone I/S mixture ratio is 15%⁃25%,and the reservoir is at the mid-diagenetic A2 stage,with secondary dissolution pores.This is the main tight-oil exploitation zone.Below 2250 m the mudstone I/S mixing ratio is less than 15%,and the reser⁃voir is accordingly at mid-diagenetic stage B.In the study area the Fuyu reservoir is divided into conventional reser⁃voir and tight-oil reservoir types I,II and III.Longitudinally,all reservoir types appear in turn with increasing depth.The most favorable reservoirs in the study area are types I and II.The most favorable exploration depth is between 1750 m and 2250 m.