Low salinity water injection is a promising water-based enhanced oil recovery (EOR) method for carbonate rocks. However, permeability impairment resulted from competition between mineral scale precipitation and rock dissolution is not well understood due to complex injection water/formation brine/rock interactions. In this paper, simultaneous effects of rock dissolution and mineral scale precipitation in low saline co-water injection on permeability performance were investigated. A dynamic flow of water with varying ion composition considering scale precipitation/rock dissolution coupling with geochemical reactions (using PHREEQC) was developed. The proposed model was validated with outlet ion concentration of single phase coreflood data. Then, permeability decline curves were obtained for each mixing ratio of formation brine and diluted sea water. The results show that in case of co-water injection, mineral scale precipitation is the dominant mechanism in early times of flooding and can be comparable with rock dissolution quantitatively in longer time. This result is in contrast with results of sequensive injection available in literature due to lack of sufficient mixing zone between injected water and formation brine and small pore volume of injection. In addition there are three different regions in permeability curve of co-water injection which is reflecting the competition between mineral scale precipitation and rock dissolution mechanisms. Moreover, as the share of formation brine increased more than 0.5, mineral precipitation became dominant and permeability curve decreased monotonically. The model can be used for distinguishing share of different mechanisms of permeability variation during low salinity waterflooding.

中文翻译：

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低盐度共注水过程中碳酸盐岩沉积/溶解耦合机制导致渗透率下降的研究

低矿化度注水是一种很有前景的碳酸盐岩水基提高采收率（EOR）方法。然而，由于注入水/地层盐水/岩石的复杂相互作用，矿物规模沉淀和岩石溶解之间的竞争导致的渗透率损害尚不清楚。本文研究了低盐度共注水中岩石溶解和矿物垢沉积对渗透性能的同时影响。考虑到水垢沉淀/岩石溶解与地球化学反应（使用 PHREEQC）的耦合，开发了具有不同离子成分的动态水流。所提出的模型通过单相岩心驱替数据的出口离子浓度进行了验证。然后，针对地层盐水和稀释海水的每个混合比例获得渗透率下降曲线。结果表明，在同注水的情况下，矿垢沉淀是驱替早期的主导机制，并且在较长时间内可以与岩石溶蚀进行定量比较。由于注入水和地层盐水之间缺乏足够的混合区以及注入的孔隙体积小，该结果与文献中的顺序注入的结果形成对比。另外，共注水渗透率曲线存在三个不同区域，反映了矿物规模沉淀与岩石溶蚀机制之间的竞争。此外，当地层卤水比例增加超过0.5时，矿物沉淀占主导地位，渗透率曲线单调下降。该模型可用于区分低矿化度注水过程中不同渗透率变化机制的份额。