低渗透油藏非线性渗流实验研究

Experimental Study on the Nonlinear Flow in Low Permeability Reservoirs

流体在低渗透岩心中的渗流不再符合达西定律,存在启动压力梯度,并且渗流曲线不再是一条直线。为了更精确地描述非线性渗流曲线,对已有实验在驱替与计量方法上进行了改进。使用改良后的实验装置,研究了膨胀性黏土矿物含量较高的砂砾岩在低流速下的渗流特征。实验曲线不通过原点,在压力梯度轴上有正截距,并且存在上弯与下弯两种形态。低渗透储层岩石喉道微细、强非均质性是非线性渗流产生的原因,并且储层岩石的特性也对非线性有一定影响。实验所采用岩心伊蒙混层以及伊利石等膨胀性黏土矿物含量高,对储层的有效渗透率影响较大。利用带喉道半径的渗流模型理论,从黏土膨胀性角度对产生非线性渗流曲线不同形态的原因进行了初步探讨。结论认为,上弯形渗流曲线之所以存在,是由于黏土膨胀减小了岩心中渗流的喉道尺寸,而使得渗流过程中流速损耗,同时也增大了启动压力梯度。

The filtering flow in the core of low-permeability does not follow Darey＇s law. There is a starting pressure in the filtering flow, and the porous flow curve is no longer a straight line. Some improvements on the existing core flooding experiments and methods of t are proposed in this paper to obtain the non-linear filtering flow curves. The low-velocity flow characteristics in a glutenite with high contents of clay-swelling minerals were studied by using the improved experimental device. The experimental curves do not pass the origin of the coordinate system,with an intercept in the pressure axis. There are two types of filtering flow curves： the upward bending curves and the downward bending curves. The tiny throat size and high heterogeneity of rock in a low permeability reservoir are the causes to make the flow nonlinear. The reservoir lithology is also responsible to the nonlinearity. The cores used in experiments with a high content of clay minerals including illite/smectite formation and illite have a significant effect on the effective permeability. Based on the theories of the seepage flow model, taking account of the throat radius, with the clayswelling ability as a target, a preliminary study is carried out on the mechanism of different nonlinear flow curves. The final results show that the clay-swelling reduces the size of the throat participated in seepage, and as a result, reduces the velocity and increases the starting pressure, which accounts for the upward bending of the nonlinear flow curves.