Acid-oil emulsion and sludge formation are known as two major formation damage mechanisms and the reason for failure of some acid treatments. The published studies in this area focus primarily on core- to well/reservoir-scale and it is fairly unclear how acid-oil interaction at the pore-scale leads to the formation damage observed at the macro- or core-scale. In this paper, dynamic, micro-scale experiments were designed and executed to investigate the acid-induced formation damage using microfluidic approach. In addition, a series of so-called static (microscope) tests were performed in which acid-crude oil compatibility tests were conducted on a glass slide followed by microscopic observation to better analyze the micromodel results.

The results show that sludge precipitation occurred right at the interface of the crude oil and acid; either with the residual oil film on the pore wall, at the acid-oil displacement menisci or acid-oil interfaces in the emulsion. Although, it is theoretically assumed that the reaction between acid and crude oil is fast, the results highlight that the damage is intensified by increasing the exposure time up to 8 hours. Besides, the acid type and concentration showed to have considerable impact on the acid-sludge and emulsion formation. The dynamic results indicate that increasing live acid concentration from 15 wt% to 28 wt% caused about 27.5% more permeability impairment due to sever pore-bridging, while spent acid did not result in any acid-sludge deposit. Furthermore, the role of ferric ion, as a transfer catalyst facilitating the two-phase contact, was visually confirmed through static tests. The dynamic tests also indicated 13% more permeability reduction when 3000 ppm ferric ion was present during 28 wt% HCl injection compared with the free-iron case.

Emulsion analysis at the pore-scale showed that acid emulsion critically plugs the pore throats and intensify acid-sludge depositions. Size of acid-oil emulsion droplets was found to be distance-dependent such that as the acid permeated deeper into the porous medium the emulsions became finer and denser causing increased damage.

Mitigating formation damage requires underpinning the mechanisms, the microfluidic approach can assist in identifying whether sludge precipitation or emulsion formation are the chief mechanisms and can serve as a fast, intermediate step before conducting the time intensive acidizing experiments at core-scale.

酸油乳化液和污泥的形成是两种主要的地层破坏机理，也是某些酸处理失败的原因。该领域已发表的研究主要集中于岩心至井/储层规模，并且还不清楚在孔隙尺度上酸-油相互作用如何导致在宏观或核心尺度上观测到的地层损害。在本文中，设计并执行了动态的微型实验，以使用微流体方法研究酸诱导的地层破坏。另外，进行了一系列所谓的静态（显微镜）测试，其中在载玻片上进行了酸-粗油相容性测试，然后进行显微镜观察以更好地分析微模型结果。

结果表明，污泥沉淀恰好发生在原油和酸的界面处。或在孔壁上残留油膜，在乳状液中的酸油置换弯液面或酸油界面处。尽管从理论上讲，酸和原油之间的反应是快速的，但结果表明，将暴露时间延长至8小时会加剧损害。此外，酸的种类和浓度显示出对酸淤泥和乳液形成有相当大的影响。动态结果表明，由于严重的孔桥作用，活性酸浓度从15 wt％增加到28 wt％导致渗透率降低了约27.5％，而废酸则没有导致任何酸渣沉积。此外，铁离子的作用 通过静态测试在视觉上确认了作为促进两相接触的转移催化剂的Cd。动态测试还表明，与不含铁的情况相比，当在28 wt％的HCl注入过程中存在3000 ppm的铁离子时，渗透率降低了13％。

孔隙规模的乳液分析表明，酸性乳液会严重堵塞孔喉并加剧酸性污泥的沉积。发现酸-油乳液滴的大小取决于距离，使得随着酸更深地渗透到多孔介质中，乳液变得更细和更致密，从而导致损害增加。

减轻地层损害需要加强机理，微流体方法可以帮助确定污泥沉淀或乳液形成是主要机理，并且可以作为在核心级进行时间密集的酸化实验之前的快速中间步骤。