Investigation of a Jetted Conductor Failure in a Pre-Salt Well and Lessons Learned

Abstract

Abstract Jetting operations have been performed, in Petrobras context, mainly in Campos and Espírito Santo Basins, where the surface casing is cemented to the mudline successfully. Lately, the company has been applying this spud-in method in pre-salt wells, mostly in Santos Basin in order to optimize the top-hole construction. This paper will focus on the analysis of a ultradeep water well which had three attempts to install the jetted conductor. The first attempt was successful but due to an operational problem in third drilling section, the well had to be abandoned. The second attempt resulted in a conductor failure, which sank into the seabed under its own weight, during the execution of the second drilling section. The third one was successful, and the well was drilled to total depth. The analysis focused in comparing the operational parameters and procedures in these three attempts. All of them were performed in close locations, therefore, it can be assumed that the soil properties are very similar in these locations. The aspects evaluated in these wells were the flow rate, the weight on bit and the conductor integrity for buckling. The retro-analysis showed that the main reason for the failure (conductor sinking into the soil) was the high flow rate used in the operation. Another observation is that the weight on bit used in the operation, in general, complied with the recommended by (Zakeri, et al. 2014), but could be increased to overcome high resistance layers while maintaining structural stability for buckling in the conductor. Petrobras has a large experience in jetting wells of Campos and Espírito Santo Basins, but the type of soil in these areas is very distinct from the Santos Basin's soil. Besides that, the wells are deeper and requires a higher axial capacity to withstand the expected loads. Therefore, the jetting technique was not meeting these needs and generated problems of conductor failure. This work brings a new proposal of actions to overcome high resistance layers and also to improve the success rate of conductor jetting in pre-salt basins.