砂砾岩储集层微观非均质性定量评价——以柴达木盆地昆北油田为例

摘要

砂砾岩储集层岩石颗粒分选差,孔隙结构复杂,存在类似双重孔隙介质特征,孔隙结构微观非均质性较强.柴达木盆地昆北油田古近系路乐河组储集层即为此类砂砾岩储集层,毛管压力曲线无"平台"部分,孔喉大小分布呈明显的多峰特征,具有"大孔-小孔"似双重孔隙介质特征.通过对储集层岩石毛管压力数据的分析,计算得出"主要流动空间百分数",可以定量表征此类砂砾岩储集层孔隙空间中大孔道和小孔道所占比例,进而定量评价此类储集层的微观孔隙结构非均质性.结果表明:路乐河组砂砾岩储集层中由"大孔"组成的孔隙空间所占比例较少,平均约占全部孔隙空间的1/3,对储集层渗透率的贡献却达到了95%,而"小孔"虽占据了约2/3的孔隙空间,但对渗透率的贡献仅为5%,说明储集层微观孔隙结构非均质性较强.%Different from the mono-pore media of routine sandstone reservoirs,glutenite reservoirs have the chara-cteristics of dual-porosity media.Lager pores and smaller pores exist in glutenite reservoir simultaneously,as a result,the pore structure is complex and the micro-heterogeneity is strong.Lulehe Formation of Kunbei Oilfield in Qaidam Basin belongs to a glutenite reservoir. The capillary pressure curves have no horizontal parts,and pores distributions are obviously bimodal.The glutenite reservoir pore space of Kunbei Oilfield can be generally divided into two pore systems,one is the larger pore system which constitutes the preferred flowing paths and contributes 95% of flowing potentiality,and another the smaller one which constitutes non-preferred flowing paths and contributes 5% of flowing potentiality only.A parameter of main flowing space percentage obtained form the data of capillary pressure is precisely to describe the proportion of lager pores to the smaller ones of reser-voir pore space,and then be used to evaluate quantitatively the micro-heterogeneity of glutenite reservoir.The results indicate that the average of main flowing space percentage in Kunbei Oilfield is 33%,that is,the larger pores take up smaller parts of reservoir pore space(about 1/3)but contribute greater permeability of the reservior,and the smaller pores take up most reservoir pore space(about 2/3)but contribute lesser flowing potentiality.The micro-heterogeneity of glutenite reservoir in Kunbei Oilfiled is severe.