A New Contribution to Cementing Technology:The Development and Field Application of a Downhole-ActivatedCentralizer
Authors: Kinzel Holger , Heidecke Karsten 
Published: October 2008

Abstract
Casing and liner cementing operations require good centralization. Common bow type centralizers make use of the elasticity of steel to create the restoring force. High restoring forces cause high moving forces. In applications such as deviated or even horizontal wells high moving forces cannot be tolerated. Diameter restrictions, like subsea BOPS may prevent the passage of centralizers equipped with strong bows.
For these cases, a downhole activated centralizer was developed. The centralizer bows are held together with a steel band. The band contains a lock, which can be released by the following parameters hydrostatic pressure, temperature or by inducing a chemical reaction.
This paper describes the development and testing of the downhole activated centralizer with a pressure- released lock, Also discussed are field applications as well as operational and safety aspect.

1 Introduction
Casing and liner cementing operations require an evenly distributed annulus around the pipe to achieve adequate mud removal. An even distribution of cement around the casing string is essential for the two basic functions of cement: to form a tight seal and to support the casing string mechanically,
The use of centralizers is common engineering practice today, Different centralizers were developed for various application, Principality, two types of centralizers exist,
The most common type is the spring bow centralizer. The second type, the rigid centralizer, is mainly used for special applications such as highly inclined or horizontal wells [1].
The typical bow type centralizer has steel bows with sufficient Elasticity to be flexible enough to pass obstructions in the boreholebut to be able to apply satisfactory force for centralization.
The restoring force always creates a friction force by the bows being pressed against the borehole wall. In many applications, this additional friction force cannot be tolerated. Therefore, the centralizer placement engineering cannot select centralizers purely by regarding the restoring force; instead a good compromise between the selection of a high restoring force combined with an acceptable moving force has to be elected.
For applications where this compromise is not adequate, a centralizer was developed which has a very low or nearly no moving force but can be activated to generate the full restoring force required, once the casing is in place. For activation, either pressure, temperature or a chemical reaction can be used. This paper discusses the development of the pressure- released mechanism.

2 Centralizer Forces
If an external force is applied radically to a spring bow centralizer, the bows create a counter force. The total reacting force of all bows of one centralizer h called the restoring force [2]. This restoring force Is a function of the spring bow shape, the material being used and the heat treating process applied to the bow. The restoring force of one single bow can be in the range of up to 750 kg (1650 Ibs), sufficient to lift up a small sized car.