Experimental Investigation on Generation and Development of Shallow Water Flow in Overpressured Sand Formation

Shallow water flow (SWF) is a common type of geological hazard in deep-water drilling. It usually occurs in a relatively shallow stratum below mud line (about 450-2500m). When encroached by a drill bit, the substantially over-pressured sand body can generate SWF that may dramatically impair the integrity of the drill string and the associated equipment. However, the mechanism that triggers SWF is lack of detailed understanding, leaving a safe design of drilling through SWF prone strata in suspense. In this paper, through the independent design and development of the shallow water flow simulation device, the damage, and flow mechanism of the sandstone occurred during the SWF events. It can be found through the experiment that in the occurrence of shallow water flow event, there is much sand accumulation around the pressure relief port. The sand body below the pressure relief port is lifted upwards as a whole, and the sand layer above the pressure relief port has a specific amplitude decrease. The findings could not only help understand the SWF process but also build a foundation for subsequent research on prevention and control of SWF incident. In addition, it provides theoretical guidance for improving drilling equipment to ensure that the SWF hazard is adequately controlled.