An Assessment Of Grouting Materials, Placement Methods, Monitoring Equipment, Placement Methods, Monitoring Equipment, And Flotation Equipment For Offshore Structures

Current grouting technology is reviewed emphasizing some of the latest developments. Main topics covered are grouting materials, grouting methods, grout monitoring techniques, recent grouting related improvements, and structure flotation equipment. Grouting materials to promote faster and higher strengths, help prevent self-desiccation, and promote faster and higher strengths, help prevent self-desiccation, and offer increased expansions are discussed. Grouts are classified according to use and typical examples are given.

A new type of lightweight admixture has been developed which can be used to formulate low density (12.5 lb/gal, 1.5kg/dm3) grouts with final strength approaching that of normal (15.6 lb/gal, 1.87 kg/dm3) density grout. Because of the vastly improved strength of this grout as compared to other low density grout, the use of such low density grouts to facilitate placement procedures warrants reevaluation.

Discussion of grouting methods covers five different techniques and their application. Several of these methods involve the use of new generation high pressure packers and flow control valves. With this new equipment, packer inflation/ grouting manifolds can be devised which enable multiple packer inflation/ grouting manifolds can be devised which enable multiple packer inflation through a single line and grout placement into multiple packer inflation through a single line and grout placement into multiple ports through a single line. ports through a single line. Improved leg plugs, conductor pipe plugs, and j-tube plugs have made structure flotation a simpler, more trouble-free operation. The plugs offer unprecedented economy and dependability. The leg plugs and conductor pipe plugs are mechanically set, retrievable, and reusable. pipe plugs are mechanically set, retrievable, and reusable

Introduction

Platform grouting refers to the grouting operations required to Platform grouting refers to the grouting operations required to provide the structural connections for the pile pinning system used provide the structural connections for the pile pinning system used to anchor a permanent offshore platform. Typical grout areas are the annuli between the skins and leg jacket and the driven piles, and the annuli around insert piles in drilled holes. This operation has advanced to the point now that an operator has a variety of methods. materials. and tools from which to choose. For example, at least five different methods for grouting platform legs are commonly used with variations existing within each method. Terms for each of these methods, although not standard. might be (1) conventional two state, (2) packer, (3) balanced pressure, (4) two stage delayed set for insert piles, and (5) two stage inner string for insert piles.

Recent advances in methods, materials and tools have helped make platform grouting more trouble-tree and dependable. The new platform grouting more trouble-tree and dependable. The new lightweight, high strength grout coupled with the high strength packers now available should make single stage grouting of most packers now available should make single stage grouting of most structures a reality.

The mechanically set plugs now available will help eliminate the worries of failure of inflation set plugs installed during platform construction.

This paper will review these advances and provide an overview of current platform grouting in general.

GROUTING MATERIALS

Offshore platform grouts are normally formulated with some type of inorganic hydraulic cement. Some grouts are simple mixtures of one cement and water but the majority of offshore platform grouts also contain one or more admixtures and small to large amounts of fine aggregate to impart specific grout properties.

The most common cements are Portland or modified Portland cements. Calcium aluminate cement is used when exceptionally high 24 hour strength is needed. Gypsum cement is limited to formulations intended for quick set plugs.

Grout Slurry Properties

An understanding of grout slurry properties and the admixture available to alter these properties can be a reliable aid in the design and evaluation of grout placement procedures and equipment. The three principle slurry properties are density, pumping time, and rheology.

Density. Grout density directly affects the hydrostatic pressure exerted by the grout. A full column of high density grout (16.7 lb/gal, 2.0 kg/dm3) will exert a differential pressure of 276 psi (1.9 MPa) at 656 ft (200 m) sea depth while a low density grout 12.5 lb/ gal (1.5 kg/dm3) would exert only 135 psi (0.93 MPa) differential pressure at the same depth. Limitations set for packer pressure, seal pressure at the same depth. Limitations set for packer pressure, seal pressure, or even jacket wall stress limit the height of grout column pressure, or even jacket wall stress limit the height of grout column which can be placed in one stage.

Another area in which density is often limited is grouting piles in drilled holes that penetrate weak formations. Large volumes of grout slurry can be lost in such formations at hydrostatic pressure equivalent to only 0.60 psi/ft (0.04 MPa/m).

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