致密砂岩储层岩电参数实验研究

Experimental Research of Rock Electrical Parameters for Tight Sandstone

目前致密砂岩油气藏的储层评价与试油气效果不好,测井解释符合率低,根本原因是没有准确求取储层的含油气饱和度。目前对致密砂岩进行储层饱和度求取,基本沿用以前评价常规砂岩储层的方法,这些方法的关键都在于高质量岩电参数的获取。由于致密砂岩孔隙度较小、孔隙结构复杂,该类储层的岩电参数获取比较困难,一般都借用同区域渗透率、孔隙度较高储层。本文根据致密砂岩的特点,选用气驱实验研究其岩电参数的变化规律。研究发现,在本文研究的致密砂岩岩心中,岩性系数b、饱和度指数n与中高孔渗储层差别较大。在孔隙度为5%—10%的致密砂岩岩心中,不同含水饱和度范围内其b、n不同,在高含水段,b基本在1左右,n在1.3—14.1之间;在低含水段,b在1.4—2.9之间,n在0.5—1.7之间。由于高含水段的含水饱和度均大于90%,因此解释时应重点关注低含水饱和度的b、n选取。利用实验结果对该岩心所在气田的4口井进行解释,证实本次实验结果更符合测试结果。

The current evaluation and testing for tight sandstone reservoirs is not as satisfactory as for conventional sandstone, with a low well log interpretation coincidence rate. The fundamental reason is that the reservoir hydrocarbon saturation can not be determined accurately. The calculating methods for the conventional sandstone reservoir saturation are used for the tight sandstone reservoirs and the key of these methods is to obtain high-quality rock electrical parameters. The rock electric parameters for a tight sandstone reservoir are more difficult to obtain because of the small porosity and the complex pore structure, so one often uses the rock electric parameters of a reservoir of higher porosity and permeability in the same area. According to the characteristics of tight sandstone, the gas drive experiments were carried out to study the variations of electric parameters. It is found that a big difference exists in the b, n values between reservoirs of high porosity and permeability and tight sandstone reservoirs. The values of b, n vary in different ranges of water saturation of the cores of 5% to 10%porosity. Under a high water saturation, the value of b is nearly 1 and the value of n is within a range of 1.3 to 14.1; under a low water saturation, the value of b is within a range of 1.4 to 2.9, the value of n is within a range of 0.5 to 1.7. Since the water saturation is greater than 90% in the high water section, the selection of b, n values of low-water saturation should be careful in well log interpretion. With experimental results being used in a few wells, these results are shown to be consistent with the test results.