Melt 2 tablespoons butter in large pot over medium-high heat. Add chicken and cook, stirring often, until chicken is no longer pink, and has begun to brown, about 10 minutes. Remove chicken to large plate, set aside.
Add remaining 2 tablespoons butter to pot. Once melted, add onion, garlic, celery, and bell pepper. Cook until softened, about 5 minutes. Stir in beans, chilies, chicken stock, salt, pepper, cumin, oregano, cayenne pepper and cooked chicken. Bring to boil, then reduce heat to low and simmer 15 minutes.
Remove from heat and stir in sour cream until evenly combined. Serve warm, with toppings of choice.