Modeling, analysis and simulation of wormhole formation in carbonate rocks with in situ cross-linked acids
Modeling, analysis and simulation of wormhole formation in carbonate rocks with in situ cross-linked acids
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DOI：
10.1016/j.ces.2012.12.019
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发表时间：
2013-03
影响因子：
4.7
通讯作者：
Ram R. Ratnakar;Nitika Kalia;V. Balakotaiah
中科院分区：
文献类型：
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作者：
Ram R. Ratnakar;Nitika Kalia;V. Balakotaiah
我们建立了一个经验流变模型来描述原位交联酸的粘度随温度、剪切速率和ph的变化。我们提出了一个双尺度连续模型来描述原位交联酸对碳酸盐的活性溶解，并将其用于分析单岩心和双岩心条件下的虫孔地层。我们使用模型的尺度分析来估计虫孔地层的最佳注入速率，并建立了凝胶和反应前沿的宽度和传播速度作为流变参数的函数表达式。我们将原位交联酸与牛顿酸的虫孔地层进行了比较，结果表明，与牛顿酸相比，原位交联酸的最佳注入速率更低，虫孔分支更多。在岩心注入速率恒定的情况下，与牛顿酸不同，原位交联酸的压力响应随注入酸的量而非单调，并且与现有的实验数据相匹配。当溶解受到动力学控制时，与牛顿酸相比，原位交联酸的虫孔尖端直径更小，穿透孔体积更小。研究结果表明，高渗透储层中较大的凝胶阻力是实现均匀增产的关键。最后，我们为原位交联酸对碳酸盐岩的最佳增产提供了一些指导。
We develop an empirical rheological model to describe the variation of the viscosity of in situ cross-linked acids with temperature, shear rate and pH. We present a two-scale continuum model to describe reactive dissolution of carbonates with in situ cross-linked acids and use it to analyze wormhole formation in single and dual core set-ups. We use scaling analysis of the model to estimate the optimum injection rate for wormhole formation and develop expressions for width and propagation speed of gel and reaction fronts as a function of the rheological parameters. We compare wormhole formation with in situ cross-linked acids to that with Newtonian acids and show that the in situ cross-linked acids lead to lower optimum injection rates and more branched wormholes as compared to Newtonian acids. For the case of constant injection rate through a core, unlike for Newtonian acids, the pressure response for in situ cross-linked acids is non-monotonic with the amount of acid injected and matches with available experimental data. When dissolution is kinetically controlled, the wormhole tip diameter is smaller and pore volume for breakthrough is lower for in situ cross-linked acids as compared to that for Newtonian acids. We identify the mechanism of flow diversion and show that the larger gel resistance in high permeability zones is the key to achieve uniform stimulation. Finally, we provide some guidelines for optimal stimulation of carbonates with in situ cross-linked acids.