Completion fluids that are introduced to the reservoir during gravel-pack operations often cause formation damage that can substantially reduce production potentials. Most gravel-pack operations employ fluid loss preventive methods to manage this problem. However, in the scenario in which gravel packing is attempted from a floating vessel such as a semisubmersible rig or drill ship, an additional problem, rig heave (wave motion), must also be addressed; the effects of rig heave compound fluid-loss problems and require additional controls in the gravel pack system. Conventional systems have attempted to manage the problem by adding seals and collets for locating the workstring; however, these additions considerably increase the cost of the systems and have not adequately addressed both gravel packing and fluid loss prevention needs.
This paper will describe a new compact weight-down gravel pack system that has been successfully used on floating vessels for gravel packing. The traditional systems that have been used on floating vessels for the same purpose will also be described. Case histories will illustrate how the new system provides solutions to the difficulties normally experienced in offshore gravel packing. Of particular interest are the following advantages that use of the new system provides:
Operational costs are reduced since less rig time is required.
Tool reliability is enhanced because of the simplicity of the system.
No chemicals are required for fluid-loss prevention.
Formation exposure to fluid loss immediately after gravel packing is in most cases eliminated.
Other applications are being proposed for the new system, and these will also be reviewed.