Mechanisms of Shallow Waterflows and Drilling Practices for Intervention

Geopressured water sands near the mudline in deep water, greater than 1,000 ft, have been shown lo be hazards when these sands are permitted to flow outside structural and 20-in. conductor pipe. Special drilling practices are required to contain the pressure during drilling and casing operations. Four mechanisms have been identified as causes of shallow waterflows: (1) induced fractures, (2) induced storage, (3) geopressured sands and (4) transmission of geopressure through cement channels. Geoscience techniques have been developed to aid in the detection of the shallow waterflow mechanisms, prior to drilling. These techniques include seismic stratigraphic interpretation of shallow hazard airgun data and specially processed threedimensional surveys, and special pore pressure and fracture gradient prediction methods. Drilling and cementing practices have been developed to minimize the risk of inducing flow behind structural and conductor casings. Each of these flow mechanisms require adapted drilling and cementing practices to prevent potentially damaging flow. This paper presents best practices developed by this operator along with our contractors to detect, drill, case, and cement shallow waterflows in the deepwater Gulf of Mexico. These practices should be transferable to other similar sites around the world.