Client

International oil and gas producer

Project location

Offshore Australia / Timor Leste

Product

• Drilling centralizer - conductor deck 37” lightweight
• Drilling centralizer - subsurface 37 - 41” variable OD

Time period

2018

Key achievements

• First light weight robust 37” drilling centralizers
• Superior borehole alignment
• Lowest borehole inclination
• Improved drilling performance

BACKGROUND

One of the areas identified for potential improvement during the Operator’s previous drilling campaign concerned the level of noise and platform vibration generated during top hole drilling. Lateral movement of the unsupported drill string within the conductor guide cans caused repeated impact on the secondary platform structure producing high levels of noise and vibration. An engineered solution was sought to reduce noise and vibration for the 2018 infill drilling campaign.

During the previous campaign, a single Matrix designed variable OD drilling centralizer had been used in the lowermost conductor guide can for the main purpose of aligning the 36” borehole with the conductor guide cans and contributing towards centralization of the conductor inside open hole. As a secondary benefit the impact of the drill string on the guide cans and the associated vibrations transferred to the platform structure were reduced. For the 2018 drilling campaign Matrix was requested to propose an additional centralizer solution at conductor deck level for further mitigation of vibration and noise during top hole drilling.

THE CHALLENGE

Design of an additional centralizer at conductor deck level presented Matrix with several conflicting design criteria with the main challenges being:

• Unknown lateral impact/loads
• Weight restrictions (<50kg; manual handling only)
• Split design (removable with drill string in place).

THE SOLUTION

The concept was developed around combining polymer materials for energy absorption and conventional materials for the lightweight framework required to ‘fill’ the 38” ID conductor guide can. The structure was designed for energy input levels, back calculated from experience gained during the previous drilling campaign. The prototype of the new centralizer was designed and manufactured within a short timeframe, with only minor modifications required to settle on the final design. A new polymer formulation was developed for the bumper subs and the casting method trialled to ensure good adherence between the different materials.

The existing design of the variable OD centralizer was modified and improved to also allow the activation feedback force to be adjustable. Both centralizers were placed on top of the motor sleeve stabiliser and deployed with the drill string. The new centralizer seated in the conductor deck guide can, while the variable OD centralizer travelled to just above the seabed where it was remotely activated to seat inside the lowermost subsea guide can.

THE RESULT

Installation and running of the centralizers on the drill string was without challenge and did not hamper the make-up of the BHA.

The conductor deck centralizer seated well in the conductor deck guide can, while the variable OD centralizer was successfully deployed in the lower-most guide can. The top hole section took 12 hours to drill during which time the string was continuously rotated at 20 rpm and the conductor deck centralizer was observed to receive continuous lateral impact from the drill string.

The centralizer proved well capable of absorbing the short/hard impacts from the drill string, transforming the load-deflection relationship, and transferring a much lower peak load to the platform. Additional energy dissipation, due to the natural hysteresis of the polymer materials employed, resulted in much lower levels of noise and vibrations than previously experienced. Noise and vibration had been successfully reduced to an acceptable level.

The Operator considered the centralizer combination a resounding success. Besides the benefits in reducing noise and vibration, the well was drilled to one of the lowest inclinations (0.42°) of all the platform wells drilled to date. The improved alignment of the drill string within the conductor guides assisted in achieving this remarkable result.

In addition to providing the drilling centralizer solution for this infill drilling program, Matrix developed a new MarineShield™ product and supplied the Polyurethane centralizers for the 30” conductors. Provision of cold cutting services for 30”, 20” and 13 3/8” casings completed Matrix’s contribution to this infill drilling program.

Publications

Case study: Drilling centralizers improving top hole drilling performance