基于常规测井的低渗透储层孔隙结构评价

Evaluation of pore structure in low permeability reservoirs based on common well logs

低渗透储层孔隙结构的已有研究主要是孔隙特征测试方法和测井新技术研究,利用常规测井进行储层孔隙结构评价是亟待解决的难点问题。以蒙古国的塔南凹陷白垩系低渗透储层为例,将薄片观察、岩石孔渗测试、压汞测试与测井资料分析相结合,以储层品质指数为纽带,间接实现非取心井段储层孔隙结构表征参数(孔喉半径均值和排驱压力)的常规测井解释,对储层孔隙结构类型进行评价。结果显示,本区发育孔隙连通型、孔隙半连通型、裂缝-微裂缝连通型和致密型4种孔隙结构类型的储层,以第Ⅲ类和第Ⅳ类为主,每类储层的储集空间类型、毛管压力曲线特征、孔渗特征等都不同。W30井与W49井试油段分析表明,储层孔隙结构类型对低渗透储层的油气产能具有控制作用。

The pore structure of low permeability reservoirs has important influences on the porosity, permeability and oil productivity.It is a hot point in the low permeability reservoir study.Most of the pore structure studies are focused on laboratory test methods and new well logging technologies.A method of evaluating the reservoir pore structure of low permeability reservoirs is urgently needed.In this study,the low permeability reservoir of Cretaceous in the Tanan depression is taken for example. The thin slices,porosity and permeability tests,capillary pressure test are in combination with the well logs.Reservoir Quality Index is chosen to realize the common well logs interpretation of pore structure parameters （average radius of pore and throat,replacement pressure）indirectly.The pore structure types of the reservoir are evaluated with these parameters.In the study area,there develop the reservoirs with four types of pore structure including the pore-connection type,pore semi-connection type,fracture and microfracture type and tight type.The first and second ones are the main types.The storage space type,the capillary pressure curve and the porosity and permeability properties of each reservoirs are different.Analysis of the well testing sections for Well W30 and Well W49 show that the pore structures of the reservoir controls the oil productivity of low permeability reservoirs in the study area.