Deep Sea facts: Safeguarding our precious deep sea environment

Extracting natural resources is a process full of incredible science, cutting edge technology and heavy manpower. We are now more successful than ever at delivering the vital energy that powers our economy, safeguarding our precious deep sea environment and ensuring New Zealanders fully benefit from our reservoirs of oil and gas.

Locating exactly the right spot to drill takes a lot of science.

Seismic survey boats traverse a wide area trailing equipment that sends sound waves deep into the ocean floor.

Various layers of rock reflect back different signals, and this data is captured by scientists onboard.

We are going to break down the drilling process into three stages - spudding in, BOP installation and drill process.

0m seafloor

sedimentary basin

oil reservoir

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Step:1 Surveying the sub-surface

As the waves bounce off layers of rock beneath the seafloor they are picked up by sensors called "geophones" towed behind the survey vessel.

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Step:2 Analysing the data

The information gathered is relayed to computers on the ship. Geologists can analyse the data to determine the presence of hydrocarbons.

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Benefits of using drillships

Drillships have many benefits over the traditional oil rig. Most importantly they can decouple and sail to safe harbour before a storm hits.

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DPS

In deeper waters drillships use multiple computer controlled engines called dynamic positioning systems(DPS) to hold in position above a well, despite wind, wave and current motion.

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Drillships size

To give you an idea of the size of these ships you could lie two rugby fields lengthwise along side. Their overall length is around 228m (748 feet).

Employed in deep and ultra-deep waters, drillships work in water depths ranging from 600 to more than 3,000 metres.

As exploration gets deeper, our drilling rigs need to be able to reach deeper too. Todays ultra-deep drillships hold equipment capable of drilling down to 12000m. Most oil reservoirs lie around 3000m below sea level.

This process is called ‘Spudding in’ and this casing forms the backbone of the whole drill site.

When the desired depth is reached we ‘case’ the hole all the way down with steel tubing. Then we pump cement right to the to the bottom which backfills up the gap between the rock wall and the outside of the steel tube to lock it in place, providing essential strength and stability.

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Well casing

First we push a ‘casing’ tube about 100m into the ocean floor. In the drilling industry this is called “the spud”.

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22” casing

Next we drill down through the casing up to 1000m (that’s one kilometre!) and insert another smaller casing tube. The hole is only about 50 centimetres wide at this point.

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Cementing the casing

A cement slurry is then pumped between the casing and allowed to harden to permanently fix the casing in place. After the cement has hardened, the bottom of the well is drilled out, and the process continues.

Once drilling is complete, a Blow-Out Preventer (BOP) is lowered onto the well opening, to effectively seal the well.

The BOP uses huge and immensely strong valves to contain any excessive pressure within the well, facilitating a constant, controlled release of oil and gas to the surface.

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Remotely operated vehicles

ROVs have become an important tool in deep sea drilling. Capable of working in waters up to 3,000m deep. These are a valuable tool used for monitoring the drill process.

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Riser pipe

For the duration of the well’s life the BOP is connected to the drill ship via a rigid tube, or ‘marine riser’. Any fluid or gas rising from the well comes through the marine riser directly to the ship for processing.

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Blowout preventer (BOP)

BOPs come in two main types: ram and annular. BOP stacks frequently utilize both types, typically with at least one annular BOP stacked above several ram BOPs.

Once the well casing and BOP have been installed we then drill out the final hole (only about 20cm wide) to the required depth.

Different drill bits are used for different results. Core bits are used to gather formation cores for logging purposes, mill bits remove cuttings from the well and tungsten carbide bits cut through harder rock formations.