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Pore-scale insights into sludge formation damage during acid stimulation and its underlying mechanisms

Mirkhoshhal, S. M ; Sharif University of Technology | 2021

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  1. Type of Document: Article
  2. DOI: 10.1016/j.petrol.2020.107679
  3. Publisher: Elsevier B.V , 2021
  4. Abstract:
  5. 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. © 2020 Elsevier B.V
  6. Keywords:
  7. Chlorine compounds ; Crude oil ; Emulsification ; Emulsions ; Microfluidics ; Petroleum analysis ; Porous materials ; Precipitation (chemical) ; Acid concentrations ; Compatibility test ; Emulsion formation ; Formation damage ; Microscopic observations ; Permeability impairments ; Permeability reduction ; Sludge formation ; Dynamics ; Catalysis ; Crude oil ; Damage mechanics ; Displacement ; Emulsion ; Fluid injection ; Porosity ; Precipitation (chemistry) ; Sludge
  8. Source: Journal of Petroleum Science and Engineering ; Volume 196 , 2021 ; 09204105 (ISSN)
  9. URL: https://www.sciencedirect.com/science/article/abs/pii/S0920410520307464