致密砂岩动态渗吸排驱核磁共振在线实验——以松辽盆地北部扶余油层为例

NMR online experiment for dynamic imbibition drainage of tight sandstone:A case study of Fuyu reservoir in northern Songliao Basin

为进一步明确致密油藏动态渗吸过程基质孔隙的动用特征,分析闷井渗吸转排驱的时机对致密油开发效果的影响。利用核磁共振在线扫描开展致密砂岩渗吸排驱过程中不同孔隙流体动用实验,选取松辽盆地北部扶余油层致密砂岩岩心,开展动态渗吸排驱与核磁共振联测实验,结合矩阵转换法建立弛豫时间与孔隙半径的关系,量化分析渗吸排驱过程中基质内油和压裂液的分布情况,并推算了基质渗吸作用距离。结果表明:压裂液渗吸阶段,大孔主要起渗吸排油通道作用,中孔和小孔对渗吸采收率起主要贡献,占总渗吸采收率的75.22%,渗吸速度在前8 h内保持较高水平,初期由中孔和大孔贡献,中期以小孔和微孔为主;渗吸96 h转排驱后的总采收率和压裂液返排率达到最高值,分别为40.73%和55.38%;实验模拟的基质动态渗吸作用距离约为11 cm,通过相似原理换算出现场闷井时间30 d。研究成果对松辽盆地致密油开发方案制定具有指导意义。

In order to further understand mobilization characteristics of matrix pores in dynamic imbibition process of tight reservoirs and analyze the influence of the time of well soaking imbibition converted to drainage on tight oil development effect,online NMR scanning is used to carry out experiments on different pore fluid mobilization in imbibition and drainage process of tight sandstone.Tight sandstone cores of Fuyu reservoir in northern Songliao Basin are selected to perform combined-test experiment of dynamic imbibition drainage and NMR,establish relationship between relaxation time and pore radius combining with matrix transformation method,quantitatively analyze oil and fracturing fluid distribution in matrix during dynamic imbibition drainage process,and calculate matrix imbibition distance.The results show that,in fracturing fluid imbibition process,macropores mainly play a role as imbibition drainage channels,while mesopores and small pores make contribution to imbibition recovery,accounting for 75.22%of total imbibition recovery.Imbibition rate remains high level in the first 8 h,which is contributed by mesopores and macropores in early stage and dominated by small pores and micropores in middle stage.After 96 h of imbibition and converting to drainage,total recovery factor and fracturing fluid flowback rate reach the maximal values,which are 40.73%and 55.38%,respectively.Experiment simulated dynamic imbibition distance of matrix is about 11 cm.Field soaking time is 30 d calculated through similarity principle.The research results have guiding significance for development plan design of tight oil in Songliao Basin.