Hole openers: When your black gold is between a rock and a hard place

Published 08.09.2015

When drilling top holes in extreme formations with rock hard boulders, the borehole can sometimes change direction, because the drill bit always chooses the path of least resistance. It needs to be guided by a firm hand – the hole-opener. With 8 tons of steel rotating and grinding into the formation above it, the drill bit will go right where you want it.

David and Goliat

In Odfjell Well Services we call them Boulder Busters. The first one measured 26″ – 36″ and was deployed by BP. It did a great job when it was launched and became a popular tool for top hole drilling.

Three years ago, ENI Norge, the operator of the Goliat field, gave us a challenge. They needed equipment that could meet the formation challenges in the Barents Sea, so they asked us:

– Can you make a bigger hole opener?

They had performed simulations that suggested that 28″ – 42″ would be an ideal size for the well type they were planning, with a large conductor that would allow for transportation of more cuttings.

What they needed was a David to fight their Goliat – and we accepted the challenge.

The solution

We started out with a 17 ton block of steel and machined it into a single piece weighing 8 tons – a complicated process that took weeks!

Our new “David” also needed to be sturdy, not just heavy. Therefore we went with TCI cutters (Tungsten Carbide Insert), instead of Mill Tooth cutters – otherwhise, the formations would eat up the teeth.

The design of the cutters is patented by Transco, a company with some 40 years of experience in producing drill bits and hole openers. 

What makes the cutters so special is the way they are connected to the hole opener; even when hitting boulders head on at full speed (120-150 rpm) they won’t get knocked off. Traditional hole openers are made up totally different and are much more vulnerable to extreme formations with boulders. 

The result was the Boulder Buster 28″ – 42″, bespoke engineered for Goliat, and tailored for top hole drilling in extreme formations. 

Busting boulders in the Barents Sea

Since 2012, the hole opener has been the obvious first choice when oil companies have planned their top holes in the Barents Sea. Subsequent to the development of the Goliat field, the Boulder Buster was used in the drilling of 3 exploratory wells in the Barents Sea for ENI Norge in 2012. These were Odden (PL 318), Bønna (PL 529) and Salina (PL 229).

A few months ago, in February 2015, the Boulder Buster was used for drilling five top holes with the same BHA (Bottom Hole Assembly). Taking into account Goliat’s extreme formations, that is quite an achievement. (Three to four holes would be a normal lifespan in environments like this.)

One of the main challenges of top hole drilling is to achieve a vertical section that deviates no more than 1.5 degrees. Due to its high weight and unique cutter design, the Boulder Buster has fulfilled these requirements.

As of August 2015, the hole opener has drilled 9 out of 10 top holes at the Goliat field.

Results and benefits of a kingsize hole opener

It is hard to determine whether or not the Boulder Buster drills faster than other hole openers. However, a vertical top hole requires less time spent on reaming and making other rig adjustments.

Because much of the weight is on the end of the string, you don’t need to push it, as the gravitational force pulls it perfectly downwards. 

Senior Drilling Engineer at ENI Norge, David Winteron, also pointed out to us other benefits, the first one being related to HSE.

Due to the Boulder Buster’s “one piece” design, there is less need for rig tongs and personell in red zone. Another benefit is that the master bushing only needs to be moved one time when the tool is lowered through the rotary table – a time saving of 2-3 hours.

By: Tor Helge Hestetun & Trond Inge Mitchell

Tor Helge and Trond Inge work as Sales & Project Engineers at Odfjell Well Services in Stavanger, and worked together on the ENI Boulder Buster project.

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