Drilling on Old Father Thames

Rotary drilling should be a straightforward process, but when it needs to be done over water it requires a special set of skills as Colin Hiscock of YourEnvironment explains.

Colin Hiscock
 YourEnvironment loading a rotary rig onto a jack-up barge

YourEnvironment loading a rotary rig onto a jack-up barge

Our client approached YourEnvironment for a cable percussive hole to 12m and then rotary follow-on to 35 with standard testing, logging and sample taking. Seems simple? Not when you are in the middle of the River Thames, reliant on tides to get the rigs loaded and ships are waiting in the English Channel (at enormous expense) to dock and unload their precious cargo of petrochemicals to the dock you are on.

As we are all aware, drilling a borehole on land can be technically and logistically challenging and can throw up all sorts of unknowns. Those challenges are multiplied when drilling over water, on a jack-up platform and to a very strict timescale. YourEnvironment was required to work through 24 hours as it was responsible for the shutdown of a petrochemical loading dock.

These pressures could have caused those small issues that always arise to become compounded. However, the cool-headedness of the drilling crews and the engineer led to the project being delivered early and without incident.

The design of a new loading dock always requires investigation to be carried out. Our client chose YourEnvironment for our experience in drilling on shore. We have completed several projects for different proposed facilities. They always involve drilling in interesting places. Recently we were tasked with drilling through a Ministry of Defence pier in the West Country, in the UK.

In addition to the difficulties of drilling over water, this project was reliant on tides and YourEnvironment was required to load the drilling rigs when the tides were correct.

So, Monday morning at 06:30 we loaded a cable percussive rig, rotary rig, casing, core boxes, liners and engineers onto the jack-up platform, which was then floated out to the location using a tug.

These platforms are immensely versatile and allow us to operate anywhere on the Thames and other shallow waters. For the uninitiated, a jack-up is a floating platform with legs at each corner. The barge is floated out to the location with the legs retracted. The legs are then lowered and the deck is lifted about 2m above high tide. Therefore, providing a stable working platform from which to drill.

At this point, the deck is about 8m from the bottom of the Thames meaning we have to lower casing down very carefully. Essentially, passing 8m of heavy casing down through fresh air and water takes a lot of skill if we do not want to lose it to the bottom of the Thames.

Drilling was simple enough with the cable rig and we were finished by 4 am the following morning. At this point, the cable rig was de-rigged and moved to the side to allow the rotary rig to be moved into position.

Passing 8m of heavy casing down through fresh air and water takes a lot of skill if we do not want to lose it

Again, the rotary drilling was simple enough and was completed ahead of time. All the while, a YourEnvironment engineer was in attendance, making sure samples were taken and that the logistics of getting the crews swapped over was carried out efficiently. The challenge on this job was ensuring virtually no time was wasted in the change-over between drilling methods or crews. We had to drill 24/7, no matter what.

The rotary reached the end of the 25m hole and pulled off. We had to do the whole exercise in reverse now so that the cable percussive crew could pull its casing. So, once that was done, samples were stowed, rigs were chained to the decks in preparation for the short trip back up the Thames to the dock were we initially loaded.

Job finished, client happy and no-one ended up going for an unexpected swim. At the end of every project, the team sit down and work through lessons learnt and what can be improved for next time. We have got years of experience in this sort of drilling and it is always best to employ a contractor with experience, especially when looking to shut down a petrochemical loading dock.