针对鄂尔多斯盆地锦58 井区开发过程中存在的高含水、气水同出等问题,开展基于致密砂岩储层孔喉尺寸划分结果评价不同储层因素对可动流体的影响,有助于从微观角度明确气体分布规律.以下石盒子组 10 个典型致密砂岩样品为例,采用铸体薄片观察、扫描电镜观测、X射线衍射分析、高压压汞及核磁共振实验,利用多重分形理论及核磁共振参数转化孔喉分布方法,评价储层参数对不同尺寸孔喉内部可动流体分布的影响.研究结果表明,根据压汞曲线形态及参数可以将孔隙结构划分为3 种类型:Ⅰ类样品孔喉尺寸分布曲线呈双峰状,物性和孔喉连通性较好;Ⅱ类样品孔隙孔喉尺寸分布曲线呈单峰状,孔喉以中孔为主,分选较好,受限于孔喉尺寸,储层物性差于Ⅰ类样品.Ⅲ类样品孔喉尺寸分布曲线小孔为主峰,大孔为次峰,其物性非均质性最强.据孔喉尺寸及分形特征曲线转折点可以将储层孔喉划分为大孔(0.1～1 μm)、中孔(0.01～0.1 μm)和小孔(0.001～0.01 μm).可动流体主要大孔和中孔内部,其中大孔含量对可动流体的含量起决定性作用,而中孔在占比较高的情况下具有一定的储气潜力,小孔含量则对可动流体分布影响不大.脆性矿物的含量主要影响大孔内部的可动流体含量,而黏土矿物的含量对不同尺寸孔喉内部的可动流体含量均产生不利影响.不同尺寸孔喉所贡献的孔隙度与可动流体含量成正相关,但受限于储层连通性的影响,随着孔喉尺寸的降低,其相关性逐渐下降,而渗透率则控制着不同孔喉尺寸内部的可动流体分布.孔喉结构参数中,较高的分形维数对储层整体及不同尺寸孔喉内的可动流体分布均有不利影响.而受限于不同孔喉尺寸对物性的贡献,最大进汞饱和度参数仅可用于表征大孔内部的可动流体分布.

In response to issues such as high water cuts and simultaneous gas-water production during the development of the J58 well block in the Ordos Basin,this study evaluates the influence of various reservoir factors on movable fluids based on pore-throat size classification in tight sandstone reservoirs.This helps to clarify the gas distribution pattern from a microscopic perspective.Taking 10 typical tight sandstone cores from the Shihezi Formation as examples,casting thin section observation,scanning electron microscopy(SEM),X-ray diffraction(XRD),high-pressure mercury intrusion(HPMI),and nuclear magnetic resonance(NMR)experiments were conducted.Using multifractal theory and NMR parameter-based pore-throat distribution transformation methods,the impact of reservoir parameters on the distribution of movable fluids within pore throats of different sizes was assessed.The results show that based on the shape and parameters of mercury intrusion curves,the pore structure can be divided into three types.Type Ⅰ shows a bimodal distribution of pore-throat sizes,with good physical properties and connec-tivity;Type Ⅱ shows an unimodal distribution dominated by medium-sized pores,with good sorting,but due to limited pore-throat size,their physical properties are inferior to Type Ⅰ;Type Ⅲ have a pore-throat size distribution dominated by nanopores as the main peak and mesopores as the secondary peak,with the strongest heterogeneity in physical properties.According to the turning points in pore-throat size and fractal characteristic curves,the pore throats can be classified into mesopores(0.1～1 μm),micropores(0.01～0.1 μm),and nanopores(0.001～0.01 μm).Movable fluids are mainly found within mesopores and micropores,where the mesopores content plays a decisive role in the volume of movable fluids,while micropores,when in relatively high proportion,also have certain gas storage potential.Nanopores,however,have little impact on movable fluid distribution.The content of brittle minerals mainly affects the amount of movable fluid in mesopores,whereas clay mineral content has a negative impact on movable fluid content across all pore-throat sizes.The porosity contributed by different pore-throat sizes is positively correlated with movable fluid content;however,this correlation decreases as pore-throat size decreases due to the influence of reservoir connectivity.Permeability controls the distribution of movable fluids within pore throats of different sizes.Among pore-throat structure parameters,a higher fractal dimension negatively affects the distribution of movable fluids both overall and within pore-throats of different sizes.Owing to the limitations imposed by differing contributions of pore-throat sizes to reservoir properties,the maximum mercury saturation parameter can only be used to characterize the distribution of movable fluids within mesopores.