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Pore-Scale Investigation of the Effect of Fracture and Mineralogy on Formation Damage Caused by Drilling Fluid

Nikbin, Hadi | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53693 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Mahani, Hassan; Masihi, Mohsen
  7. Abstract:
  8. Formation damage in petroleum engineering is an important and fundamental phenomenon. During drilling operation, penetration of either the solid phase of drilling fluid or the base-fluid into the porous medium, reduces the permeability of the formation. While most experiments in the literature have focused on core-scale and beyond, there is lack of pore-scale studies. Moreover, presence of fractures has an undeniable effect on the extent of formation damage. Thus, the main objective of this dissertation is to investigate the effects of fractures on the severity of formation damage caused by the water-based drilling fluid and the mechanisms of formation damage at the pore scale, using glass micromodel. In design of experiments, the effect of the number of fractures, fractures openings (width) and orientation have been considered. The effect of pH and addition of silica nanoparticles to the drilling fluid for remediation of the damage has also been studied.In the carried-out experiments, first the micromodel was fully saturated with crude oil and then the drilling fluid was circulated within the well annulus of the micromodel and penetrates into the porous medium. Hydrochloric acid was then injected into the micromodel as a cleaning/stimulation fluid to remove the damage and restore the formation permeability. In the final stage, in order to mimic production stage of reservoir, the oil was flowed back into the micromodel.It was observed that at each stage of the micromodel experiments, various types of formation damage occur. During the injection of drilling fluid into the micromodel, the permeation of filtrates and solid particles of the drilling fluid into the micromodel causes formation damage and changes in the structure of the porous medium. Also, in the micromodel cleaning stage, hydrochloric acid penetrates to the pore space between the solid particles of drilling fluid and to the surface of the micromodel. In the oil production phase, as a result of the contact of acid and oil, emulsions are formed in porous medium, which significantly reduces the permeability of the micromodel.The results of micromodel experiments show that the presence of fractures increases the length of the damaged zone. In addition, once the drilling mud enters fracture, it penetrates more easily into the porous zones adjacent to the fracture which causes secondary formation damage. Moreover, the results demonstrate that the number of fractures, fracture widths and their orientation influence the length of damaged zone and severity of damage. Overall, detailed examinations show that the presence or the absence of the fracture in the micromodel is the most important factor in comparison with other physical and geometrical characteristics of fractures.Furthermore, based on the results of rheology and filtration tests, it was found that the presence of silica nanoparticles improves the properties of drilling mud such as filtration volume, plastic viscosity, yield point and the thickness of mudcake. Addition of silica nanoparticle was found to reduce mud invasion to porous medium by forming a stable mud cake. However, there exists an optimum concentration depending on mud pH. The optimum concentration of the required nanoparticles for the drilling fluid at low and high pH was determined to be 0.4 wt% and 0.6 wt%, respectively. It was also found that the required concentration of nanoparticles was not strongly dependent on the physical characteristics of the fracture.The results of this study demonstrate the applicability of using micromodels to visually observe the performance of drilling fluid and identify the damage mechanisms. By identifying the mechanisms, a suitable remedy can be then identified
  9. Keywords:
  10. Formation Damage ; Silica Nanoparticles ; Fracture ; Glass Micromodel ; Pore-Scale Model ; Water-Based Drilling Fluid

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