Abstract The paper is aimed at describing the series of actions taken to re-entry a well whose (wet) Christmas-tree-cap was clogged by hydrate buildup and therefore could not be released by means of a regular releasing tool. A deepwater well located in Campos Basin, offshore Rio de Janeiro, Brazil, was the scenario for this unique job. To our best understanding the kind of approach used to solve this hydrate problem has never used by industry before. A patented thermochemical method – the so-called self-generated nitrogen (SGN) method–was applied to heat and dissociate the crystallized hydrate, which was clogging the tree-cap-locking-pin's piston chamber. Heat application around the body of the Christmas tree enabled us to dissociate the hydrate and release the tree cap by means of its regular retrieving tool. This paper describes all the steps taken to perform this pioneer workover job. As a matter of fact, a multidisciplinary task that encompassed the following points: - development of a "tailor-made" environmental-friendly SGN formulation, - heat exchange simulations to design the optimum volume for the SGN treatment batch, - a review of the theoretical aspects of hydrate formation/dissociation, - mechanical modifications of the (regular) tree-cap releasing tool and, - a meticulous job and safe procedures review.