Experimental Investigation of Stimulation Fluid Induced Formation Dmaged Using Micromodel

Mirkhoshhal, Mehdi | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52387 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Mahani, Hassan; Ayatollahi, Shahaboddin
  7. Abstract:
  8. Acidizing as the most frequent stimulation technique in the field, has been extensively used to increase the production rate. Even though acidizing treatments is well established, there is still an inherent risk for self-induced formation damage through incompatibilities of the fluids involved in this process.
    A main potential problem during acidizing is the incompatibility of the acid and the reservoir’s crude oil. Acid interaction with crude oil can produce two major damage mechanisms that could offset partially, if not totally the benefit of the acid stimulation. These mechanisms are the rigid film emulsion formation and the acid-sludge precipitation, result in well productivity reduction and higher operational costs. The potential detrimental impacts of acid-sludge formation include, near-wellbore permeability reduction through plugging of different types of pore spaces (pores, throats, vugs, wormholes and natural fractures), alteration of rock wettability and increasing the stability of emulsions which leads to higher apparent viscosity. The published research works in this area address predominantly this challenge through field and core-scales experimentation. Studies at these scales inherently do not provide direct pore-scale insights into the underlying mechanisms of the observed behavior at macro- or core-scale. In the present research, the formation of acid-sludge at pore-scale was investigated using microfluidic technique which, to our knowledge has not been reported already. To further analyze the microfluidic results, a series of static tests were conducted by contacting acid-oil at different conditions on a microscope slide. To better understand the emulsion and acid-sludge induced damage mechanisms in porous media, the effects of HCl concentration, the presence of ferric ion, the crude oil type and acid-oil exposure time as the most important reported parameters were investigated. Besides, for first time, other important parameters related to the characteristics of porous media such as wettability, pore size and structure effects as well as the acid injection rate were investigated. The microscope-slide and micromodel results revealed that among various influential parameters, acid concentration has the largest impact on the risk of emulsion and acid-sludge formation, also as oil-acid contact time increases, sludge precipitation increases. The quantitative values derived from micromodel experiments showed that by increasing acid HCl concentration from 15% to 28%, the absolute permeability reduced by 27%. Also, the presence of iron ions in high concentration acids shows a more severe effect on sludge precipitation. The results also showed that porous medium wettability would affect the sludge and emulsion formation significantly by controlling the amount of residual oil and acid-oil contact. In the oil-wet porous medium, the acid-sludge formation increased due to the presence of thicker oil layers on the surface of the pores which results in more surface contact of oil and acid. This caused permeability reduction through pores bodies and pore throats plugging. As for the acid HCl 28% in the presence of 3,000 ppm iron ion, by changing the wettability of the porous medium from the mixed-wet to the oil-wet state, a 12% absolute permeability reduction of the micromodel was observed. Moreover, investigation of the acid injection rate and its effect on the intensification of acid-oil emulsions formation show that further attention should be paid to determine the appropriate acid injection rate to avoid formation damage problems in the near-wellbore and the reservoir. The micromodel results of the acid injection rate parameter show that, at the same conditions of acid HCl 28% injection, the lower injection rate caused 5% higher residual porosity. Furthermore, the results of testing the commonly used acidic additives indicate their ineffectiveness in controlling the acid-sludge precipitation at high concentrations of hydrochloric acid. As for the acid HCl 28% in the presence of 3,000 ppm iron ion, despite using of appropriate acidic additives, a significant absolute permeability reduction 65% is still measured. Lastly, the new generation of stimulation fluid used in this study, GLDA, showed very little tendency to form stable emulsions and acid-sludge precipitation. This desirable performance is due to two main reasons: lower acidic strength and the ability to control and stabilize iron ions present in the reservoir
  9. Keywords:
  10. Simulation Fluid ; Formation Damage ; Acid-Oil Emulsion ; Acidic Sludge ; Pore-Scale Model ; Micromodel

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