Is water alone sufficient to remove the impurity of urine from a spot on the body that has olive oil on it, or is it necessary to use soap, given that the oil remains after washing with water?

If impurity gets on oil applied to the body, the oil becomes impure. The impurity is removed when the oil is removed. If it is not removed except with soap, then using it is obligatory. Certainty is required regarding the impurity having affected the spot, while being cautious of obsessive doubts.