盐水相关（变矿化度）的开采过程涉及调整注入水的离子组成和矿化度，以提高石油产量。开采过程中使用的盐水类型通常是通过稀释或添加或去除注入水中的离子而产生。在过去二十年中，由于其优于其他石油开采方法，该开采过程在全球范围内进行了大量研究。近年来，实验室岩心驱油实验和现场试验等多项研究表明砂岩和碳酸盐岩储层中提高采收率的潜力，并在两个前沿领域得到了很好的探索，即盐水稀释和成分变化。然而，许多挑战给开采进程带来了负担，例如对基本化学机制的争议；难以构建代表性模型，以对过程进行可靠的解释和预测；这些都需要适用的解决方案。
因此，本研究探索了基于实验观察的多组分运移和地球化学反应耦合方程的理论公式。在数值模型的构建过程中，捕捉到了弥散/扩散、平流、瞬时平衡反应和非平衡速率控制反应等机理。DLVO表面力理论也被用于合理化决定电位的离子相互作用，并评估每个力分对油-卤水-岩石系统中润湿性变化和特征油采收率改善的贡献。该模型被用于解释最近公布的碳酸盐岩储层中盐水依赖开采过程应用中探索的不同方法的结果。
Geochemical Modeling of Oil-Brine-Rock Interactions during Brine-Dependent and Brine-CO2 Recovery Technique in Carbonate Petroleum Reservoirs
Abstract
The brine-dependent recovery process involves the tweaking of the ionic composition and strength of the injected water compared to the initial in-situ brine to improve oil production. The type of brines used during the recovery process is often generated through the dilution or addition or removal of ions to/from the available injection water. The recovery process has seen much global research efforts in the past two decades because of its benefits over other oil recovery methods. In recent years, several studies, ranging from laboratory coreflood experiments to field trials, admit to the potential of recovering additional oil in sandstone and carbonate reservoirs and has been well explored on two frontlines, namely, brine dilution and compositional variation. However, many challenges have saddled the recovery process, such as disputes over the fundamental chemical mechanisms; difficulty with construction of a representative model to give reliable interpretation and prediction of the process; and these necessitate applicable solution.
Therefore, this study explores the formulation of theory based on experimentally observed behavior to couple equations of multicomponent transport and geochemical reactions. Mechanisms such as dispersion/diffusion, advection, instantaneous equilibrium reactions and nonequilibrium rate-controlled reactions are captured in the construction of the numerical models. The DLVO theory of surface forces was also applied to rationalize potential determining ion interactions and to evaluate the contribution of each force component to the wettability change in the oil-brine-rock system and the characteristic oil recovery improvement. The model was applied to interpret recently published results on the different approaches that have been explored in the application of brine-dependent recovery process in carbonate reservoir rocks. The focus being that identifying the dominant mechanisms responsible for the observed improved recovery will help substantiate the field application of the process.
Hence, the model was utilized to explore brine-dependent recovery application beyond the lateral propagation that could be achieved in 1D coreflood experiments by considering an areal propagation of a 2D large-scale model with similar properties as reported in the published experimental experiments. Analysis of sensitive parameters like thermodynamic constants, rock surface site density and area, the viable link between wettability alteration and oil recovery, mineralogical content variation, injection strategies and pore volumes, were carried out to determine their influence on the process performance. Then, the model was extended to investigate the intrinsic oil-brine-rock interaction during a system of combining low saline brine and CO2 injection.
The study demonstrates that injected brines, containing potential determining ions depleted in NaCl, are more effective at improving recovery when it, and wettability alteration is much more pronounced at high temperatures. It was also illustrated that potential determining ion concentrations play a more significant role as compared to brine salinity reduction. The magnitude of the contribution of the electrostatic force to sustaining a stable water film increases with decreasing ionic strength, either through reduction of NaCl, Ca2+ or brine dilution, or increasing SO42- concentration. Mineral dissolution/precipitation is necessary for the pursuit of reestablishing equilibrium and should not be ignored in modeling different mineralogical carbonate rocks. The derived optimized thermodynamic parameters are demonstrated to be widely applicable. Although chalk and limestone differ by surface area and reactivity, the same thermodynamic parameters are applicable in modeling the recovery process in their respective reservoir rocks. There is a significant increase in relative injectivity for brine-CO2 recovery mainly due to more exposure to a higher amount of CO2-saturated-brine.
Overall, brine-dependent recovery is relatively inexpensive and environmentally friendly, offers more advantage than other chemical EOR methods in terms of operating costs, field implementation and environmental assessment, even though it might recover comparably less additional oil. Additionally, low saline brine can serve as pre-conditioner for other EOR methods, as most of the injected chemical/gas performs better under low saline brine.
Keywords: smart waterflooding; low salinity waterflooding; potential determining ions; interfacial mechanisms; carbonate rocks; wettability alteration; oil-brine-rock interactions, surface sorption and complexation, water film stability, geochemical modeling, low salinity-water-CO2.
