Warm the oil in a stockpot over medium heat. Add the shrimp shells, onions, carrots, and celery and saute for 15 minutes, or until lightly browned. Add the garlic and cook 2 more minutes.
Add 1 1/2 quarts of water, the white wine, tomato paste, salt, pepper, and thyme. Bring to a boil, then reduce the heat and simmer for 1 hour. Strain through a fine sieve, pressing the liquid from the solids. Makes approximately one quart.