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Keeping it central

Oilfield Technology,

Iain Levie, Antelope Oil Tools, USA, introduces a cost-effective solution for use in deepwater drilling.

While many in the oil and gas industry are facing strong challenges to navigate through challenging times, Antelope Oil Tools is utilising this volatile time to research, develop and innovate new technologies that will optimise well construction efforts, specifically in casing running and cementing applications.Companies that are actively drilling wells must make their operations as efficient and cost-effective as possible in 2016 and beyond to adjust to today’s market, and the near term forecasts for the industry. Antelope is dedicating significant resources to develop more efficient and cost-effective solutions that are designed to provide an economic benefit without sacrificing performance and reliability.

One of the major challenges associated with drilling deepwater offshore wells is that annular clearances are extremely tight, making the challenge of obtaining maximum stand-off capacity when centralising casing in deepwater well formations increasingly difficult. The most common approach has been to utilise centraliser subs in tight tolerance well applications. However, the company’s ‘On-The-Pipe-Solutions’ offer operators another alternative in many cases for centralising casing strings by installing its CentraMax® Close Tolerance (CT) Centraliser(s) and WearSox® thermal spray directly onto the casing joints, eliminating the additional cost of an integral sub body threaded onto the end of a casing joint, which adds length to the pipe and risks of additional potential leak paths within the casing string.

Traditional centraliser subs are costly due to the premium threading requirements (to match the casing connection) and body material that is required to meet or exceed the burst, collapse and tensile strength requirements of the casing design.

Alternatively, ‘On-The-Pipe-Solutions’ eliminate these costs by more than 60% in many cases with their direct on-the-pipe installation method. The (CT) centralisers cost per unit is substantially lower than a standard centraliser sub due to the reduced material needed to manufacture the centraliser, lead time and maintenance required. The design reduces lead-time by weeks, if not months, in certain applications. With shorter lead-times, cash flow is greatly improved because the operator has the ability to manage expenditure commitments closer to when the product is required. The CT Series also diminishes the maintenance expense to installed and racked centralisers by offering protective coatings. Antelope’s onto-the-casing direct installation method manages casing string changes and negates requirements to manage and warehouse supplementary inventory. Unlike the CT Series, subs require the operator to hold an inventory longer than necessary, raising the risk of the product becoming obsolete and resulting in additional costs.

Manufactured from a single-piece of 100% heat-treated steel, CT centralisers have a restoring force, ideal for all well conditions. The CT Series includes the RT1, PI1 and PT1 models that offer different anchoring geometrics and allow the operator to choose the design that provides optimum centralisation in any given well. The different designs allow for the casing string to be pushed in, rotated in or pulled in through the wellbore.

Green Canyon Field

The challenge:

While drilling on a deepwater project in the Green Canyon Field, Whistler Energy, LLC required a centralisation package for their 3834 ft length of 5.5 in. production liner. Whistler Energy desired to run the production liner to a depth of 11 034 ft. The liner was required to pass through a 6.5 in. restriction by previous casing, into a 7.5 in. under-reamed open hole section.

The application required a centralisation product with attributes for providing low starting and running forces for smooth passage through the restriction, and high restoring forces to centralise the liner inside the under-reamed hole. It was also desired that the centraliser would allow for both reciprocation and rotation. Lastly, the solution was required with a short lead time.

Figure 1. This is a rendering of the CentraMax® PI1 On-The-Pipe-Solution™ Centralizer (Push-In Technology)

The solution:

To meet the challenge, the company recommended the CentraMax PI1 Centraliser and WearSox external stop collars. The CentraMax PI1 is a one piece centraliser that is designed to be pushed when installed between two external anchoring devices, and is used when radial annular clearance between casing OD and restriction ID are sufficient. For this specific project, the technology was the best on-the-pipe-solution.

The result:

Using the CentraMax PI1 and the WearSox Stop Collar, the customer was able to get the casing straight to bottom with no problems resulting in a successful cement job.

Gulf of Mexico

The challenge:

An operator drilling in the Gulf of Mexico was faced with a difficult casing string application that required it to run a very deep/heavy weight 16 in. liner to a record depth, in a deviated and under-reamed well bore. Rather than utilise centraliser subs (a more standard offering), the company opted to run their ‘On-The-Pipe-Solution’ as an alternative.

Well parameters:

In the Walker Ridge Field, drilling in 7000 ft of water, the operator was required to run the 16 in. casing through an 18.25 in. ID restriction at the 18 in. supplemental hanger and through an 18.125 in. ID restriction at the 22 in. casing shoe track. The 16 in. liner was to be run to 24 000 ft and centralised in a 21 in. under-reamed hole with 22° of inclination. The liner was a mixed string of 16 in. 97# and 16.15 in. 127# casing and weighed more than 2 million lb. The weight was such that the operator would not have been able to POOH after the shoe reached 19 000 ft, making the centralisation even more critical.

The solution:

Antelope’s team recommended using the RT1 single piece centraliser with WearSox internal thermal spray metal stops. The RT1 provides clients a technically superior alternative to in-line centraliser subs. It is pulled in both directions when used with WearSox internal stops. Because of its one-piece design, the RT1 represents improved mechanical integrity, high yield and tensile strengths and eliminates the potential of failure of welds, a critical differentiator when considering the weight of the casing string.

The result:

Using the RT1 with a WearSox internal stop, the customer was able to run the casing to the bottom and accomplish their objective of a successful primary cement job. In addition, the client also realised a savings of greater than 60%, by installing centralisers directly to the casing, as opposed to using in-line centraliser subs.


In nearly all instances, CentraMax ‘On-The-Pipe-Solutions’ proved themselves as a suitable alternative solution to centraliser subs when annular clearances allow for installing products to the casing itself. However, when the annular clearance is smaller than ¾ in. a centraliser sub is required because the restriction area is simply too tight. In these cases, deepwater centraliser subs are manufactured by utilising the CentraMax CT one-piece centralisers and installing them directly onto the threaded sub body. The CentraMax Centraliser Subs are available with pull-through, rotating and push-in technology. Antelope aims to offer cost-effective and dependable solutions regardless of the challenges associated with reaching total depth and achieving a successful primary cement job.

Figure 2.  This is a rendering of the CentraMax® PT1 On-The-Pipe-Solution™ Centralizer (Pull-Through Technology)

Figure 3.This is a rending of the CentraMax® RT1 On-The-Pipe-Solution™ Centralizer (Rotating Technology)

Edited from an article written by Iain Levie

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