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Experimental Investigation of Asphaltic Sludge Formation Caused by Asphaltenic Oil Carbonated Reservoir Acid Stimulation

Mohammadzadeh Shirazi, Meisam | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51660 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical Engineering
  6. Advisor(s): Ghotbi, Cyrus; Ayatollahi, Shahab
  7. Abstract:
  8. Acidizing is one of the most effective techniques to remove the formation damage and restore (or even increase) the permeability of the near wellbore region. Although this technique is widely used to resolve the skin problem, it could initiate new damages itself that hinder the fluid flow and decrease the well production, consequently. Acid-oil emulsion and sludge formation are known as two major induced formation damage and the main reasons for the oil well acid treatment failures.When the HCl is reacted with asphaltenic crude oil during matrix acidizing, it results in unexpected damage at the near wellbore region and hinder the fluid flow through certain mechanisms include:
    1- Pore body filling through the asphaltic sludge formation
    2- Fluid viscosity buildup through the emulsification
    3- Rock wettability alteration caused by the asphaltic sludge deposition
    In the present research, these mechanisms are systematically investigated. The acid-oil emulsion and asphaltic sludge formation were evaluated quantitatively using multiple compatibility tests between HCl and crude oil (as well as synthetic oil) samples. The acid concentration, ferric ion presence, and acid-mixture ratio were selected as the main factors affecting the emulsion stability and the amount of sludge formation. To mimic the real condition the interference of the effects of these factors was noticed besides the crude oil type. Other effective parameters like temperature, pH and exposure time are also studied. In addition, the acid-oil interaction behavior inside the porous media is investigated using glass visual micro-model and sandstone acid core flooding. The wettability alteration effects owing to the sludge deposition on different rocks is investigated through contact angle and adhesion tests.The results revealed that controlling the iron ion presence, choosing the best acid concentration, and regulating the acid-mixture ratio would drastically reduce the risk of emulsion and sludge formation. This would critically help to prevent the damage without any preventative additives presence. The quantitative values derived from this experimental work showed that the weight of dried asphaltic sludge formed was diminished to 7%, 5.6%, 2.4%, 22%, 7.5% and 10% of the most critical sludging condition for the crude oil samples A, B, C, D, E, and F, used in this study from different reservoir, respectively. The results also confirmed that the sludging behavior is extremely crude oil type case sensitive and in addition to the oil composition, other properties such as the oil viscosity and density would affect the sludge and emulsion formation significantly. It is important to note that, the de-asphalted part of the crude oil contributes mainly in the sludge formation. Therefore, asphaltene is not the sole responsible component or even a prerequisite for sludge formation. The results show that the wettability of water wet sandstone is changed quickly to oil wet during its contact with sludge mixture. However, no wettability alteration is seen for carbonates. This phenomena is attributed to different electrical charge of sludge, which is also measured in this study, and sandstone rock which leads to sludge adsorbtion. The sludge and emulsion formed through crude oil and live (or spent) acid contact would result in 69% (42%) permeability decrease in the porous rock during the flooding tests. Finally, the results of this study would provide the new insight related to sludge and emulsion induced formation damages and proposing new techniques to minimize the risk of these damages during the acidizing process
  9. Keywords:
  10. Reservoirs Acidizing ; Formation Damage ; Sludge ; Acid-Oil Emulsion ; Wetting ; Porous Media

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