缝洞型碳酸盐岩气藏多类型储层内水的赋存特征可视化实验

Visual experiments on the occurrence characteristics of multi-type reservoir water in fracture-cavity carbonate gas reservoir

缝洞型碳酸盐岩气藏非均质性强且孔隙结构复杂,多类型储层内水的形成过程与赋存模式难以确定,影响储层内气体渗流能力与气井生产动态预测。将岩心CT扫描与微电子光刻技术结合,设计并研制了3种储层的微观可视化模型,开展气驱水物理模拟实验,定性研究了水的形成机理与赋存模式,并利用ImageJ灰度分析法定量研究了不同压差下的含水饱和度及残余水膜占比变化规律,综合分析了多类型储层内水的赋存特征及其对气体渗流的影响。结果表明:天然气在不同类型储层中的运移成藏过程不同;多重介质中的水由原生可动水和残余水组成,而残余水又分为次生可动水和束缚水;残余水主要以“水膜”、“水团”、“水柱”和“水珠”4种模式赋存在不同类型储层的不同位置,其主要影响因素有毛细管力、表面张力、气驱压差和通道连通性;可动水、残余水饱和度是与储层物性、孔隙结构和气驱压差直接相关的参数;流动通道尺寸越小,相同气驱压差下水膜占据的空间越大,且水膜占比呈指数性增加;随着气驱压差增大,水膜占比减小,当气驱压差增大到一定程度时,水膜占比基本不再减小,形成“薄膜”型束缚水。

Fracture-cavity carbonate gas reservoirs have a strong heterogeneity and a complex pore structure,in which the formation process and occurrence patterns of water in multi-type reservoirs are difficult to determine,affecting the flow ability of reservoir gas and the prediction of production performance in gas wells.In this paper,the core CT scan images are combined with microelectronic photolithography techniques to design and develop the visual micromodels for three types of reservoirs,carry out the physical simulation experiment of gas flooding water and qualitatively study the formation mechanism and occurrence pattern of water.In addition,ImageJ gray analysis method is utilized to quantitatively study the changing rules of water saturation and residual water film ratio under different pressure differences.The results show that natural gas has different migration and accumulation processes in various reservoirs;the water in multiple media consists of connate movable water and residual water,and the latter is divided into secondary movable water and irreducible water;residual water mainly occurs in different locations of various reservoirs in the form of"water film","water mass","water column"and"water droplet",and the main influencing factors are capillary force,surface tension,gas flooding pressure difference and channel connectivity;the saturation of movable water and residual water are the parameters directly related to reservoir physical properties,pore structure and gas flooding pressure difference;the smaller the size of flow channel is,the larger the space occupied by water film under the same gas flooding pressure difference will be,and the proportion of water film is exponentially increasing with channel size;with the increase of gas flooding pressure difference,the proportion of water film decreases,and when gas flooding pressure difference increases to a certain extent,the proportion of water film is basically no longer reduced to form the irreducible water of"thin film"type.