Pressure Grouting: An Improved Method For Offshore Structure Grouting
Authors: Tragesser A.F. , Dalton C. , Kay F.J. 
Published: December 2007

A new method for grouting the legs of offshore platforms is evaluated with respect to grout quality, economics, and reliability. A clear-plastic scale model of a typical jacket-piling assembly was constructed for flow-visualization studies. Results of the scale-model tests and field operations show that a high-quality grout column can be obtained with the new method and that the process is economically and operationally feasible.

Introduction

Methods for grouting the legs of offshore oil structures commonly used today inject the grouting material into the bottom section of the legs near the ocean floor. This procedure requires grouting lines from the surface to the bottom of each leg. The bottom of the leg must also be sealed. Generally, inflatable subsurface packers or grout seals are used. As the grouting material is pumped into the bottom of the leg, the water inside the leg is displaced through a surface vent. Injection is continued until grouting material of the desired specification is noted at the surface vent. In some situations, divers are used to remove the grout lines and the packer inflation lines.

Satisfactory results are not always achieved with these conventional methods because of the following.The sealing system could sustain damage during platform installation that would not allow it to platform installation that would not allow it to support the full column of grout. This would result in incomplete filling of the leg with grout.The injected grouting mixture could overrun static water in the leg and leave water pockets or water channels. This overrun water would significantly reduce the strength of the grout in those local areas.The platform jacket might have substained unknown damage that would allow the grouting material to leak out after placement.

Any damage-caused leak will be more easily detectable before grouting using the pressure grouting technique. The leaks are detected by observing the pressure required for displacing sea water from the pressure required for displacing sea water from the annulus. If the displacement pressure is less than the hydrostatic bead pressure, a leak is present. The value of the pressure indicates the depth at which the leak occurs. This new method offers substantial economic savings in most cases. Operator experience shows improved reliability.

This paper discusses the results of a scale-model study of this method, describes the field experience gained, and briefly describes the operational procedure. procedure. This method is called the "pressure method." The details of the method have been previously disclosed in U. S. Patent No. 3,601,999, granted to Max Bassett and Horace Olsen Aug. 31, 1971. The authors believe this to be the first published report concerning the laboratory and field performance of the method.

Purpose of Model Purpose of Model Since the inside of a platform leg could not be observed during the grouting operation, it was necessary to build a transparent scale model to demonstrate the viability of the pressure grouting method.

JPT

P. 495