Influence of ultra-low interfacial tension system on nonlinear seepage law of low permeability core
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摘要: 低渗储层中启动压力梯度导致流体渗流规律呈现非线性特征，使得低渗储层的开发方式与中高渗储层不同。为了研究新立油田低渗储层中的非线性渗流现象，以新立油田天然低渗岩心为研究对象，通过精密压力测试多孔介质渗流实验分析超低界面张力体系对新立油田低渗岩心中单相及两相流体启动压力梯度的影响。研究结果表明：对于任何流体，新立油田低渗岩心均表现出非线性渗流特征，存在着一定启动压力梯度；低渗岩心拟启动压力梯度的值高于启动压力梯度，且两者均随着渗透率的提高而降低且与渗透率之间均为幂关系；超低界面张力体系可以明显地降低低渗岩心最小启动压力梯度与拟启动压力梯度；对于不同渗透率的岩心，两相临界启动压力梯度与含水饱和度的关系均表现出相似的变化规律，即两相临界启动压力梯度随着平均含水饱和度的上升先上升后降低；在不同渗透率下，对比水驱和超低界面张力体系驱的临界压力梯度最高点，超低界面张力体系下的临界压力梯度最高点明显小于水驱，这表明界面张力的减小可以明显地降低驱油时产生的两相临界压力梯度，超低界面张力体系改善了油藏的注入性。本研究对新立低渗储层水驱后开发方式的选择提供了参考。Abstract: The starting pressure gradient in low permeability reservoir leads to the nonlinear characteristics of fluid flow, which makes the development mode of low permeability reservoir different from that of medium and high permeability reservoir.In order to study the nonlinear seepage phenomenon in the low permeability reservoir of Xinli Oilfield, taking the natural low permeability core of Xinli Oilfield as the research object, the influence of ultra-low interfacial tension system on the start-up pressure gradient of single-phase and two-phase fluid in Xinli low permeability cores was analyzed through the porous media seepage experiment of precision pressure tests.The results show that for any fluid, the low permeability core of Xinli Oilfield shows nonlinear seepage characteristics, and there is a certain threshold pressure gradient.The value of pseudo starting pressure gradient of low permeability cores is higher than that of starting pressure gradient, and both of them decrease with the increase of permeability, and the relationship between them is power.The ultra-low interfacial tension system can obviously reduce the minimum starting pressure gradient and quasi starting pressure gradient of low permeability cores.For cores with different permeability, the relationship between the two-phase critical starting pressure gradient and water saturation shows a similar change law, that is, the two-phase critical starting pressure gradient firstly increases and then decreases with the increase of average water saturation.Under different permeability, the highest critical pressure gradient of water flooding and ultra-low interfacial tension system flooding is compared.The highest point of critical pressure gradient in ultra-low interfacial tension system is obviously smaller than that in water flooding.This shows that the decrease of interfacial tension can significantly reduce the two-phase critical pressure gradient during oil displacement, and the ultra-low interfacial tension system improves the injectivity of the reservoir.This study provides a reference for the selection of development mode after water flooding in Xinli low permeability reservoir.
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图 6 渗流速度与拟启动压力梯度关系图
Figure 6. Relationship between flow velocity and pseudo starting pressure gradient
图 7 不同渗透率岩心原油单相渗流时压力梯度与流速关系
Figure 7. Relationship between pressure gradient and flow velocity of oil percolation with different permeability
图 8 启动压力梯度与渗透率的关系拟合曲线图
Figure 8. Fitting curve of relationship between starting pressure gradient and permeability
图 9 拟启动压力梯度与渗透率关系拟合曲线图
Figure 9. Fitting curve of relationship between pseudo starting pressure gradient and permeability
图 10 不同单相流体的流速启动压力梯度关系
Figure 10. Relationship between velocity and starting pressure gradient of different single phase fluids
图 11 不同渗透率岩心水驱和超低界面张力体系驱临界启动压力梯度随含水饱和度变化曲线
Figure 11. Curve of critical driving condition and water content of produced fluid changing with water saturation with different permeability
图 12 不同渗透率岩心超低界面张力体系临界启动压力梯度变化率
Figure 12. Variation rate of surfactant WL critical driving pressure gradient in cores with different permeability
表 1 岩心参数
Table 1. Basic parameters of experimental cores
井号 岩样编号 岩样长度/cm 岩样直径/cm 孔隙度/% 气测渗透率/10-3 μm2 吉检1 S1-2 6.552 2.500 14.91 1.974 吉14-8 S1 5.864 2.460 16.95 3.340 吉检1 S6-2 7.060 2.472 14.50 5.990 吉10-18 S4-2 6.794 2.472 15.76 8.170 吉+2-014 S103 4.520 2.510 15.30 13.865 吉1-12.1 S43 3.746 2.492 13.46 14.222 吉+2-014 15-2 7.240 2.510 17.56 24.010 吉1-12.1 S51 3.766 2.490 15.74 36.759 吉检3 S2-1 6.000 2.470 15.61 40.794 吉+28-015.1 2-1 6.650 2.480 15.42 46.200 
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表 2 表面活性剂复配体系
Table 2. Properties of the surfactant formulas
复配类型 比例 溶液总体积分数/% AEO/SDS 3∶1 0.25 HSB-16/SDS 7∶3 0.25
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表 3 实验方案
Table 3. Experimental scheme
驱替剂 渗透率/10-3 μm2 模拟地层注入水 1.974, 3.340, 5.990, 8.170 AEO/SDS 1.974, 3.340, 5.990, 8.170
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