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OTC Technology Review: Downhole Products

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Oilfield Technology,

The Offshore Technology Conference (OTC), held each year in Houston, Texas, US, is one of the world's leading upstream oil and gas events. Before OTC 2020 was cancelled due to the COVID-19 pandemic, Oilfield Technology contacted a range of key players in the upstream industry and asked for their insight on the latest technologies that were due to be showcased at this year's OTC.

In this submission, Keith Bradford, Downhole Products, UK, delves into the technology the company has developed in response to the challenge of keeping casing centralised in close tolerance wellbore applications.

As well designs are becoming increasingly challenging, with deeper and longer casing strings, the requirement for additional casing seats has grown. This carries an increased operational complexity, as casing has to be deployed through tighter restrictions while maintaining good centralisation for effective cement displacement. The process of under reaming makes the wellbore diameter larger than the previous casing size, which assists with cement displacement. However, keeping the casing centralised in the wellbore is the key challenge.

Downhole Products (DHP) has developed EXPAND-O-LIZER ASLO® centralisers and SPIR-O-BITE® slimline collars in response to the challenges of casing deployment and effective centralisation in these close tolerance wellbore applications.

Figure 1. EXPAND-O-LIZER ASLO centralisers and SPIR-O-BITE slimline collars are engineered for close tolerance wellbore applications.

Conventional bow spring type centralisers are designed to flex and pass smaller restrictions, but in extreme cases of close tolerance, casing must pass an annular gap as small as ½ in. and still be expected to centralise casing in a larger wellbore with an annular gap greater than 2 in. diameter.

Specialist centralisers able to withstand the significant running stresses observed in these applications are required. Standard bow spring type centralisers cannot routinely withstand the loads applied and still maintain high performance levels. It is imperative to deliver high levels of restoring force to maximise centralisation in the larger wellbore.

Balancing optimum centraliser restoring force with the low running drag forces required to efficiently deploy the casing string is key in extended reach wells, where available surface weight may be restricted and additional applied loads may induce pipe buckling.

The EXPAND-O-LIZER ASLO centraliser was developed to operate in challenging under reamed and close tolerance conditions. The single piece design includes integrated stress relief features and engineered blade geometry. The blade profile allows the centraliser blades to flex and dissipate high stresses at varying intervals over the blade when run into and through tight restrictions, without generating high resistance and running forces.

Once the centraliser has passed through the restriction(s) and into the under reamed wellbore, it consistently returns to its original profile with high restoring forces and effective casing centralisation, which optimises the success of subsequent cementing operations.

Casing centralisers are routinely run together with stop collars, which capture the centraliser on the casing. However, in close tolerance applications the running diameter of these collars often exceeds the annular gap. Conventional stop collars are run with grub screws, which restrict how much the running diameter can be reduced.

DHP’s SPIR-O-BITE slimline collar is an engineered solution with no grub screws and high holding force. With holding forces significantly in excess of conventional grub screw-type stop collars and a quicker, simpler installation method, there is no impact on field operations. The ‘twist on’ collar grips the casing without complex installation tools, allowing fitting to be carried out in almost any environment. An integral anti back-off feature removes the risk of the collar becoming loose on the casing.

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