Heat olive oil and butter in a skillet over medium-high heat. Cook celery, sweet onion, and garlic until the onion is translucent, about 5 minutes.
Combine rice, green onions, raisins, curry powder, salt, saffron, and cayenne pepper in a 9x13-inch baking pan; stir well. Stir in the celery mixture and chicken stock. Cover pan tightly with aluminum foil.
Bake in the preheated oven until rice is tender, about 35 minutes. Let stand for 5 minutes; fluff with a fork.