TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractGas hydrate formation during deep water offshore drilling is a well known operational hazard. Drill stem testing of gas reservoirs in deep water poses an even more hazardous potential since thermodynamic inhibition is sometimes ineffective because the well can produce more water than expected. This paper describes the formation and dissociation of a hydrate plug formed during a deepwater wildcat testing operation in the Espírito Santo Basin, offshore Brazil. Hydrate formation occurred despite continuous alcohol injection. The plug was formed in the annulus between the coiled tubing (CT) and the string above the mud line (1400m water depth), jamming the CT and avoiding string retrieval. Hot water was injected into the CT for plug removal without success although computer simulations showed an inflow temperature well above hydrate dissociation temperature for the given pressure. A thermochemical reaction fluid for in situ heat generation was further injected into the CT with no positive results. Since thermal methods failed in dissociating the plug, a depressurization scheme was designed involving retrieving CT by cutting it out just above the hydrate plug for allowing liquid removal from the drill string. Depressurization was successful in dissociating the hydrate plug in a relatively short time. Operational procedures, lessons learned and possible reasons for failure of thermal methods are discussed.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe present study describes the steps taken to drill the final section of an exploratory well in Santos Basin in the underbalanced (UB) condition, in 1,500-m (4921-ft) of water depth. The first well in the area reached a fractured carbonate reservoir in which massive losses of circulation caused so many operational difficulties that the formation evaluation was not conclusive. As consequence, in the third quarter of 2005, another well will be drilled, reaching the same reservoir in the UB condition. Pre-planning and planning activities, additional required equipment, riser modifications, and new procedures are presented and discussed.