In a large saucepan, heat oil and butter and add celery and onions, sauteing until translucent. Add flour to make a roux. Add clam juice and mix well to integrate flavors. Reduce heat to low, add cream and bring slowly to a simmer. Add potatoes, and let cook until just fork tender. As potatoes begin to soften, stir in clams and continue to simmer until clams become opaque, but be careful not to overcook the potatoes. Season with salt, pepper and crab boil seasoning, to taste.