Geohazards in Riserless Drilling for an Exploration Well in Deepwater GoM: Identification and Mitigations

Abstract A Geohazards assessment for the riserless section is critical in offshore drilling operations, especially in deepwater environments, such as Brazil or Gulf of Mexico as there is no blowout preventer (BOP) being utilized in this section of a well. If there is any occurrence of geohazards issue without control, then it can have negative impact on human safety and the environment. Geohazards prediction and mitigation in the riserless section requires a multidisciplinary approach with specific types of data from seismic (high resolution recommended), site survey data (multibeam, sub bottom profiler, high backscatter, offset well information (mud weight, drilling trouble events) and most importantly, the geological understanding from regional to local scale. This paper presents critical input data and an integrated workflow of how to identify potential geohazards and respective mitigations for planning a deepwater exploration well in Gulf of Mexico. Not only does it provide a perspective view about the geohazards prediction process, but it also shows the actual outcomes from drilling results. We will use a case study well as an example to illustrate the assessment procedure. This well was identified as a challenging well with complex shallow geology in the riserless section. Drilling trouble events were observed in most of the offset wells in the same geological setting with gumbo, tightspots, shallow water flow and shallow gas. High-definition seismic data was recommended and incorporated into shallow subsurface interpretation and geohazards prediction. We derisked the uncertainty of riserless drilling through the shallow section of the prospect area for upcoming wells, and successfully drilled the riserless section despite the challenging shallow geology.