Application of Low-Salinity Waterflooding in Carbonate Cores: A Geochemical Modeling Study
低矿化度水驱（LSWF）是一种通过改变原油/盐水/岩石相互作用以提高采收率的技术，尤其在复杂碳酸盐岩中效果显著。本文通过数值模拟（基于实验岩心驱替数据）研究了二价阳离子（Ca²⁺和Mg²⁺）在液相与碳酸盐岩表面交换对润湿性改变的影响，成功历史拟合了实验中的采收率和压降数据。结果表明，润湿性改变是LSWF提高采收率的主要机制（通过相对渗透率曲线的交叉点偏移体现）。敏感性分析表明，LSWF注入时机、速率和温度等参数对过程有显著影响。
CMG软件解决方案
- 模型构建：
- 采用CMG的GEM™*件进行组分模拟，建立一维非均质碳酸盐岩岩心模型（30×1×1和40×1×1网格）。
- 考虑地球化学反应（离子交换、矿物溶解/沉淀）和流体流动耦合，模拟海水（高矿化度）与低矿化度水驱替过程。
- 关键机理模拟：
- 多组分离子交换：以Mg²⁺和Ca²⁺的等效分数作为润湿性改变的插值参数，调整相对渗透率曲线。
- 矿物反应动力学：模拟方解石（CaCO₃）溶解和白云石（CaMg(CO₃)₂）沉淀对孔隙度和渗透率的影响。
- 毛管力效应：采用Skjaeveland模型，历史拟合实验压降数据。
- 历史拟合与验证：
- 成功拟合实验采收率（误差<5%）和压降数据，验证了模型的可靠性。
- 通过敏感性分析优化注入参数（如二次采油阶段早期注入LSWF效果更佳）。
结论
- 主要机理：多组分离子交换（SO₄²⁻、CH₃COO⁻、Ca²⁺、Mg²⁺）是润湿性改变的核心，导致相对渗透率曲线向更亲水方向偏移。
- 注入参数影响：
- 时机：二次采油阶段（早期）注入LSWF比三次采油阶段（后期）提高采收率更显著。
- 速度：较高注入速度（0.5 ml/min）通过增强物理驱替提高采收率。
- 温度：高温（110°C）促进Mg²⁺吸附和矿物反应，但对采收率影响较小。
- 模拟方法：基于阳离子交换的模型比阴离子交换模型更准确，验证了地球化学模拟的必要性。
Abstract
Waterflooding is the most widely applied improved oil recovery technique. Recently, there has been growing interest in the chemistry and ionic composition of the injected water. Low-salinity waterflooding (LSWF) is a relatively recent enhanced oil recovery technique that has the ability to alter the crude oil/brine/rock interactions and improve oil recovery in both clastics and carbonates. In this paper, the increase in the recovery factor during LSWF was modeled based on the exchange of divalent cations (Ca2+ and Mg2+) between the aqueous phase and the carbonate rock surface. Numerical simulations were performed using laboratory coreflood data, and oil recovery and pressure drop from experimental works were successfully history matched. The ion exchange equivalent fractions, effluent ions concentrations, changes in mineral moles, and pH have also been examined. Besides, an investigation of multi-component ionic exchange as a mechanism responsible for wettability alteration during LSWF in heterogeneous low-permeability carbonate cores is presented. The results show that wettability alteration is responsible for the increase in oil recovery during LSWF, as reflected by the shift in the crossover points of the relative permeability curves. A sensitivity study done on many key parameters (e.g., timing of LSWF injection, injection rate and temperature) and the mechanistic modeling method revealed that they all have huge effects on the process.
作者单位
- 尼日利亚大学
- 挪威科技大学（NTNU）石油工程系。
