Technology from Europe:
United Kingdom

BHP Billiton found new centralizers beneficial

Unique simulation software proved to be an important factor in the success of BHP Billiton’s casing operation in Lennox field in the East Irish Sea basin, Fig. 1. The program – used by UK centralizer manufacturer Centek Ltd. – enabled the company to provide accurate load prediction and to optimize the distribution of 110 centralizers along the casing string. According to BHP Billiton drilling engineer Dominic Murphy, “The centralization program gave a minimum 73% casing stand-off in 12.9-in. hole. Casing was run without any problems. The use of these bow spring centralizers gave the benefit of providing greater stand-off in over-gauge hole while being at least as robust as a solid centralizer.”

Fig. 1. BHP’s Lennox field location in the East Irish Sea.

BHP attributes part of the success of its casing running and cementation operation to the design of the new 958-in. centralizers that the company was using for the first time. Each centralizer is manufactured from a single piece of boron steel using a patented cutting and treatment process, Fig. 2. This results in a low friction coefficient, which makes casing running significantly easier – of particular value for operators of horizontal or extended-reach wells. It is load tested to 68,000 lb and is capable of withstanding an angular pull at 45,000 lb. This strength, combined with resistance to wear, permanent set and disintegration, zero start force, zero running force and exceptionally high stand-off, all help ensure that the casing remains centralized to the borehole under all conditions and inclinations.

Fig. 2. Each bow-spring centralizer is manufactured from a single piece of boron steel.

The design and strength of the centralizers also maximizes flow-by area and makes it possible to undertake cementation at higher pump rates without risking formation damage. This is demonstrated by the Equivalent Circulating Density (ECD) signature that the centralizers attain.

By using the one-piece centralizers in conjunction with the proprietary software package, the BHP Billiton drilling team was able to obtain accurate predictions while running casing. The program can model numerous factors, including varying section coefficients of friction, variable densities arising from muds and cements that may be present, flotation section methods, lateral loads where the well changes direction and rotational torque at the rig floor. Drilling engineers are able to work with software experts and conduct “what if” well simulations, so that centralizer locations can be planned for optimum performance and economy. 

The centralizers are manufactured in England to a design that exceeds API 10D standards as well as the more demanding Shell SQAIR standards. The manufacturing process can quickly produce centralizers tailored to unique customer needs. These include the high performance “Slider” centralizer chosen by BHP Billiton, which is designed for far-reach horizontal, deviated and close-annulus wells. Other designs include straight bow, rigid or positive stand-off designs and different types of two-part hinged construction. The computer simulation service is used to identify the most suitable option and ensure that the user achieves optimum performance and economy through his choice of centralizer design.