Heat oil in large soup pot; add onions, celery and carrots and cook for 5 minutes.Rinse beans under cold water until water runs clear; add to onions, celery and carrots.Add chicken stock, kielbasa, 4 thyme sprigs.Salt and pepper liberallyBring to a boil; reduce to a slow simmer and cook for at least 1 hour.After 1 hour, use a potato mashers and mash some of the beans.Stir and cook for another 30 minutes.