碳酸盐岩油藏多级交替酸压指进现象模拟与影响规律分析

Simulation and Influence Law Analysis of Multi-stage Alternating Acid Pressure Fingering in Carbonate Reservoir

以多级交替注入酸压技术为代表的深穿透酸压改造工艺是近年来发展起来的一种新型压裂技术。在多级交替酸压过程中,由于酸液在裂缝中的分布与滞留机理不明确,限制了交替注酸压裂的优化设计与实施效果。针对传统的只适用于多孔介质模型油藏数值模拟方法无法精细模拟裂缝中多相流动的问题,提出了一种基于Navier-Stokes方程的CFD数值模拟方法。该方法能够基于实际酸压裂缝尺度,建立碳酸盐岩油藏酸压裂缝数值模型。在分析多级交替酸压机理的基础上,采用Fluent软件研究不同交替注酸参数下酸液的分布与滞留特征,并在此基础上优化交替注酸参数。结果表明:注酸排量为5 m^(3)/min时,“指进”现象较明显,改变黏度比主要影响酸液流动形态,密度差为1 kg/m^(3)时,酸液“指进”程度变得更加明显。结果验证了该方法的适用性,可为碳酸盐岩储层的高效压裂提供理论依据。

The deep penetrating acid pressing process,which is represented by the multi-stage alternating injection acid pressing technology,is a new fracturing technology developed in recent years.In the process of multi-stage alternating acid fracturing,the optimal design and implementation effect of alternating acid injection fracturing are limited due to the unclear distribution and retention mechanism of acid in the fracture.To solve the problem that traditional reservoir numerical simulation methods(only applicable to porous media models)cannot accurately simulate multiphase flow in fractures,a CFD numerical simulation method based on Navier-Stokes equation is proposed in this paper.This method can be used to build a numerical model of acid pressure fractures in carbonate reservoirs based on the actual scale of acid pressure fractures.Based on the analysis of the mechanism of multi-stage alternating acid pressure,the distribution and retention characteristics of acid solution under dfferent alternating acid injection parameters were studied by using Fluent software,and the alternating acid injection parameters were optimized on this basis.The results show that the"fingering"phenomenon is more obvious when the injection rate of acid is 5 m^(3)/min,the change of viscosity ratio mainly affects the flow pattern of acid,and the"fingering"degree of acid becomes more obvious when the density difference is 1 kg/m^(3).The results verify the applicability of this method,which can provide theoretical basis for efficient fracturing of carbonate reservoir.