松辽盆地白垩系营城组火山岩孔缝单元类型和特征

目前火山岩储层评价的主要依据是储集空间类型和孔渗参数,但储集空间类型与物性参数之间的关系尚不明确。为此,依据松辽盆地全取心井(营一D1井和营三D1井)开展营城组火山岩孔缝单元类型研究及其与孔渗参数关系的分析,取得如下主要认识。首先,研究区火山岩主要发育5种原生孔隙、3种次生孔隙、3种原生裂缝和3种次生裂缝;根据发育过程、分布排列特征的相似性,把储集空间归并为7种孔隙类和2种裂缝类;将上述孔隙类与裂缝类划分为7种组合类型,即7型孔缝单元,分别为①型离散气孔类-次生裂缝类组合型、②型定向气孔类-脱玻化类-次生裂缝类组合型、③型离散粒间孔类-溶蚀孔类组合型、④型离散粒间孔类-溶蚀孔类-原生裂缝类组合型、⑤型离散粒间孔类-溶蚀孔类-次生裂缝类组合型、⑥型定向粒间孔类-溶蚀孔类-次生裂缝类组合型和⑦型裂缝类组合型。其次,对比按孔隙单元拟合孔渗关系与按整体拟合孔渗关系的函数斜率,7型孔缝单元可划分为3组,即,略低于总体拟合函数(A组)的①型和②型孔缝单元,略高于总体拟合函数(B组)的③型、④型、⑤型和⑥型孔缝单元,远远高于总体拟合函数(C组)的⑦型孔缝单元。第三,除②型单元和⑦型单元之外的其他5型单元的储层物性较好;各型孔缝单元的孔喉分选系数随孔喉半径均值增大而增大,储层非均质性变强;多数孔缝单元具有复杂的岩性-岩相组合;孔缝单元分布与火山机构类型和相带关系密切。第四,依据孔缝单元的孔渗条件和孔渗相关拟合函数可知,应该依据孔缝单元进行储层评价分析,即使赋存于相同岩性的①型、②型单元也需要分别对待。

Types and Characteristics of Volcanic Reservoir Pore-Fracture Units of Cretaceous Yingcheng Formation in Songliao Basin,NE China

To evaluate volcanic reservoirs,only the parameters of porosity and permeability are now focused;while the void space,which is the controlling factor to influence the porosity and permeability, is ignored.It hampers the research of volcanic reservoirs.Types of pore-fracture units and their porosity and permeability are analyzed based on the cores of Yingcheng Formation in Early Cretaceous of well Y1D1 and well Y3D1 in Songliao basin.The main results are followings:1 )There are five kinds of primary pores,three kinds of secondary pores,three kinds of primary fractures,and three kinds of secondary fractures.The most pores and fractures have been reformed by compaction and dissolution. According to the formation process and distribution pattern,the reservoir spaces are assembled to seven kinds of pore-groups and two kinds of fracture-groups.On the basis of combined characteristics of pore groups and fracture groups,the volcanic reservoirs are divided into seven types of pore-fracture units as below:unit① assembling of scatter vesicles group (SVG)and secondary fracture group (SFG),unit②assembling of directional vesicles group (DV),devitrification pore group (DPG)and SFG,unit ③assembling of scatter intergranular pores group (SIPG)and emposieu group(EG),unit④ assembling of SIPG,EG,and primary fracture group (PFG),unit ⑤ assembling of SIPG,EG,and SFG,unit ⑥assembling of directional intergranular pores group (DIPG),EG,and SFG,and unit⑦ assembling of PFG and SFG.2)The porosity and permeability of the pore-fracture units have high value except unit②and unit ⑦.There are three groups of slope of correlation function of pore-fracture units between porosity and permeability comparing to that of the total samples.Group A includes unit ① and ②, whose slope is smaller than the total’s;Group B includes unit③,④,⑤ and ⑥,whose slope is bigger than the total’s;Group C is unit ⑦,whose slope is much bigger than the total’s.3)The pore throat sorting coefficient of pore-fracture units are positive correlation with pore throat average radius;this means that the heterogeneity of reservoir becomes stronger.Most pore-fracture units consist of complex lithology and lithofacies.The distribution characteristics of pore-fracture units are correlated to the types and facies belts of volcanic edifices.Based on the above,for reservoir evaluation,the pore-fracture units have also to be considered in addition to their parameters of porosity,permeability,and correlation function;although the units ① and unit ② bear in lava,they have distinct characteristics in porosity and permeability,and it is necessary to treat them individually.