Cementing Multilateral Well With Latex Cement
Authors: Abdul-Rahman R. , Chong A. 
Published: December 2007

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Abstract
One of the latest techniques in enhancing the current production is multilateral well. A multilateral well is a well having one or more branches or lateral sections from its main bore. The lateral sections can be open-hole or cased-hole. When they are cased-hole, the cement integrity for casing support and zonal isolation is of utmost importance. For cementing the lateral sections of multilateral wells, it is important to have a cement with high strength and durability to support the liner throughout the well's life-span. During the cutting of the cemented liner stub, the cement column is subjected to various stresses. Thus, properties such as high tensile strength, flexural strength and crack resistance are required. These properties are also important to allow a clean cut through the cement sheath without inducing too many cracks in the cement column during the above operation. Latex cement is commonly used for its gas migration control property. However, this paper presents a case history where latex cement was used primarily for the above reasons to successfully cement the first multilateral well with cemented junction in the Asia-Pacific. Operational data are presented and discussed. Laboratory data are also presented to illustrate the advantages of latex cement for this application as compared to non-latex cement. The case history and laboratory data suggest that latex cement is the solution to potential cement related problems in multilateral wells.

Introduction
Latex cement is a cement system that utilizes a latex polymer dispersion as its main component. Latex polymer dispersion is an aqueous solution of styrene and butadiene micro-particles stabilized in blends of surfactants. It is commonly known as synthetic rubber. For use with cement, a styrenel butadiene ratio of 60:40 is known to give a good balance of properties. It is either an anionic, non-ionic or a mixtures of the two, depending on the charges of the surfactants used. Because of the charges of the particles, the dispersion is sensitive to free ions which will promote coagulation. It is also known to be sensitive to temperature and mechanical energy. To further enhance the chemical and physical stability of the dispersion, a high concentration of anionic surfactant can be added to the dispersion. When the surfactants dry out, the particles form coherent and continuous films. Similarly, as cement slurry containing latex polymer dispersion hydrates, the polymer particles coalesce together and bond strongly to cement particles and other solids they come in contact with. Previous works with oilwell cement and construction cement have shown that latex cement has the following properties compared to non-latex cement.–higher flexural strength–higher tensile strength–higher crack resistance–reduced permeability–less shrinkage–better bond strength–good compressive strength–gas migration control–better rheology without using dispersant–better fluid loss control–shorter transition time–less water to cement ratio
This paper does not attempt to prove that the above are valid. Rather, it is to suggest that because of the above properties, latex cement is one of the best options for cementing lateral liners set through windows in multilateral wells.

Application
In multilateral wells, liners are set from a main bore, exiting through windows milled in the main casing strings. P. 431^