A system for monitoring a marine well for shallow water flow: Development of early detection

Abstract

Deepwater basins around the world contain shallow sequences of overpressured, sand-prone sediments that can result in shallow water flow (SWF) events. These events have frequently resulted in wellbore instability and increased man-hour exposure to potential health, safety, security, and environment risks, as well as nonproductive time, and they have sometimes been the cause of the loss of a well while drilling the shallow (riserless) section for oil and gas exploration or development projects. Methods previously established to classify the magnitude of an SWF event have been used with partial success to identify the onset of an SWF event. The need existed to develop a system enabling early prediction, detection, and mitigation of SWF events while drilling. Real-time monitoring of the riserless section of a marine well for SWF requires a system using a plurality of data feeds that we defined as the SYSTEM. The data feeds include seismic data, remotely operated vehicle video, and surface and downhole logging measurements. An SWF surveillance methodology, which we defined as a discharge category model (DCM), has been developed for early detection of an SWF event, prior to the onset of wellbore instability. DCM focuses on baseline discharge categories (ranging from no flow to minor flow) prior to wellbore instability and taking into account the U-tube effects. Real-time monitoring of data feeds coupled with DCM in the context of SYSTEM has helped to mitigate SWF events. There have been no wells lost due to SWF events that have used DCM in the context of SYSTEM in various basins throughout the world. In total, 154 wells have been monitored globally using DCM with 46 SWF events detected and mitigated before reaching a severity level that might compromise well integrity from 2012 to 2019.