致密气藏孔隙水赋存状态与流动性实验

An experimental on occurrence and mobility of pore water in tight gas reservoirs

致密砂岩气藏岩石孔隙结构复杂，一般含水饱和度较高，且其中水的分布与赋存状态及流动性等对气体渗流影响较大。通过选取苏里格气田具有代表性的不同物性岩样，开展气驱水、核磁共振、压汞等实验分析，建立了孔隙一核磁曲线交汇图，研究岩石孔隙中水的赋存特征及流动性。研究结果表明：①在砂岩储层中，水优先占据细小孔隙和大孔隙壁面，气分布于大孔隙中央。②致密砂岩细小孔喉内的水流动性差，残余水饱和度较高，其流动性与其中的气体流动密切相关，当气体流动压差（流速）较低时，只能驱动相对大孔隙中的水；随压差增大，可驱动更加细小孔隙中的束缚水。③气体可驱动束缚水的最小孔隙半径与气流压差成指数函数关系，在半径为0．05μm的孔喉中，气驱水的压力梯度约为1．78-2．22MPa／cm。因此，致密气藏中半径小于0．05μμm孔喉中的水很难流动，这部分孔喉很难成为气藏开采的有效通道。该研究结果对研究致密气藏的开采机理具有重要意义。

The rocks in tight sandstone gas reservoirs have complex pore structures and high water saturation,where water distribution and occurrence state as well as mobility have great influences on gas flow.Representative rock samples with different physical properties were selected from Silige gasfield to carry out gas flooding water,nuclear magnetic resonance,and mercury injection experimental analyses,etc.Then a 'pore-nuclear magnetic resonance curve intersection figure'was mapped to study the occurrence characteristics and mobility of water in rock pores.The research results show that in sandstone reservoirs,water is given priority to occupy the fine-pore and macro-pore walls,while gas is distributed in the center of macro pore.The water in the fine pore throat of tight sandstones presents poor mobility and high residual water saturation.The mobility of water is related to gas flow.In case of low gas flow differential pressure(flow rate),only the water in large pore could be driven;with the increase in differential pressure,the irreducible water in finer pore could be driven.The minimal pore radius of irreducible water driven by gas has an exponential function relationship with gas flow differential pressure.In the pore throat with the radius of 0.05μm,the pressure gradient of gasflooding-water is about 1.78-2.22 MPa/cm.Therefore,it is difficult for water in the pore throat with the radius less than0.05μm to flow,leading to the difficulty in taking such pore throat as an effective channel for gas reservoir exploitation,which has an important significance to study the production mechanism of tight gas reservoirs.