一种定量测定油藏岩石润湿性的新方法

A new method for determination of wettability of reservoir rocks.

在前人工作基础上，建立了一种定量测定油藏岩石润湿性的新方法，即经改进的自吸速率法。该测定方法所依据的原理是，当岩石与流体接触时，其表面的润湿性是影响自吸速率的一个关键因素。通过采用无因次时间（ｔＤ）代替实际自吸时间，可以消除油／水界面张力、液体黏度、孔隙结构，以及岩心的形状与尺寸等其它因素对自吸速率的影响。由自叹过程中所测得的拟毛管压力曲线，可定量确定岩石表面在某一特定条件下的润湿指数（ＷＲ）。 ＷＲ值越大，则水湿性越强。 ＷＲ值的大小，既取决于自吸速率，又取决于自吸的液体总量。在进行自吸实验时，将岩样吊挂在电子天平上，并浸入盐水中。盐水组成应与建立束缚水饱和度时所用盐水相同。自岩样浸入盐水的瞬间开始，记录岩样质量随时间的变化，直至岩样质量保持恒定时为止（通常约需７２ｈ）。根据每一时刻岩样质量的变化和油、盐水的密度差，求出该时刻油相的自吸采收率（Ｒｉｍ），井绘制每一岩样的Ｒｉｍ与ｔＤ关系曲线。然后分别计算不同ｔＤ值所对应的拟毛管压力（Ｐｃ，ｐｓ）和水饱和度（Ｓｗ），并绘制出每一岩样的Ｐｃ，ｐｓ与Ｓｗ关系曲线。根据该曲线的下包面积，求出每一岩样的润湿指数（ＷＲ）。实测结果表明，使用该方法测得的润湿指数与使用传统?

On the basis of previous work, a new method for the determination of wettability of reservoir rocks, which can be designated as the modified method of spontaneous imbibition, has been established. The method is provided based on the principle that the wettability of rock surfaces is a key factor affecting the spontaneous imbibition rate as the rock contacts fluids. The influence of oil/water interfacial tension, liquid viscosity, pere geometry, as well as the shape and size of core samples, can be eliminated by introducing a dimensionless time, tD, instead of the imbibition time. The wettability index of rock surfaces under a given condition, WR, was determined quantitatively from the pseudo capillary pressure curve measured in the process of imbibition. The larger the value of WR is, the stronger the water wetness will be. The magnitude of WR depends on the rate of spontaneous imbibition and the total volume of the imbibition liquid. The imbibition tests were conducted by suspending a core from an electronic balance and immersing it in brine. The constitution of brine used in this test should be the same as the brine used for establishing the initial water saturation. The change in weight of the suspended core versus time was monitored for the period of time from core immersing to the weight of the core keeping constant (usually 72h). The oil recovery by spontaneous imbibition, Rim, at a given time was calculated and the curve of Rim versus tD, was plotted from the change in core weight and the density difference between oil and brine. The pseudo capillary pressures, pc,ps, and water saturation, Sw, corresponding to various values of tD were calculated and the curve of pc,ps versus Sw was plotted. Finally, the wettability index, WR, for each core sample was determined from the area under this curve. The experimental results indicate that the wettability indices determined using this method is considerably comparable with the wettability indices, Iw-o, determined using the traditional Amott method. Compared with the Amott method, the accuracy of the results determined using the new method is higher, and the experimental procedures are simpler. It is therefore convenient for applying more widely. However, the method is only suitable for the determination of wettability ranging from neutral wet to strongly water-wet condition. In general, the resolving power of WR is higher for the strongly water-wet rocks, while the resolving power of Iw-o is higher for the weakly water-wet rocks.