Black gold

With the price of fuel hitting record highs it's worth considering what's actually involved with the extraction of ‘black gold' as well as its impact on our lives and the global environment. 

The Government has set a target to source 15% of UK energy from renewables in 2020. If this is achieved we will still rely on oil and gas for 70% of our needs so we are fortunate that 40% of the North Sea's oil and gas reserves are still available to be extracted.

Certainly the oil and gas industry can help to sustain the UK economy during the move to alternative energy forms. As production declines the wealth of technology and expertise that has developed in the oil and gas industry during the past 40 years, such as the material and process experience Premier Deep Hole Drilling has gained will become increasingly important to further wealth creation.

First, the marine technology, skills and expertise pioneered in oil and gas are important in the design, installation and maintenance of offshore wind turbines and therefore, have a role in the continuing evolution of renewable energy.

Secondly, to prevent carbon dioxide building up in the atmosphere, it can be captured and stored. Some of the best natural repositories are depleted oil and gas fields and the industry's knowledge of undersea geology, reservoir management and pipeline transport will play a vital role in enabling this process to be established in the UK.

Making connections

In recent years, as the North Sea industry has reached maturity, the tendency has been to use existing infrastructure for new developments. The main benefit of this is that it extends the economic life of that infrastructure, and means that small accumulations can be developed economically. Most North Sea finds now are relatively small compared with the earlier giants such as Forties and Brent, where fixed platform rigs were installed.

To develop offshore fields as economically as possible, numerous directional wells radiate out from a single platform to drain a large area of reservoir. Connecting them all together are subsea manifolds machined by Premier. These look similar to tombstone work fixtures measuring around 600mm x 200mm x 300mm and are typically produced from 316 stainless steel. With anywhere up to 90 blind, through and intersecting holes drilled into the manifolds these parts are produced on the company's prismatic knee drilling machines.

For directional drilling special weighted drill collars are used with a 'bent sub' to deflect the drill bit at a certain angle in the required direction. Wells which deviate at more than 65° from the vertical and reach out horizontally more than twice their vertical depth are known as extended reach wells. In order for the driller to guide the deviated well to a specific target zone in the reservoir a monitoring-while-drilling (MWD) 'directional sub' is run above the bit to relay information back to the surface on the bit location and inclination. This information can be transmitted to the surface using a mud-pulse telemetry system or recorded in the directional sub and recovered when the bit is changed.

Harsh treatment

Due to the company's expertise with the machining of difficult materials Premier produces the bodies and other components of the MWD equipment for a number of key customers. Managing director, Stuart Grant, explains: “Working in a harsh environment and extremely arduous conditions all oil and gas equipment has to be very reliable and robust. As such many structural parts are produced from exotic materials, including nickel and nickel-chrome alloys such as Inconel and Monel, as well as P550 non-magnetic stainless steel to remove the risk of signal disruption.”

For smaller fields, rather than being drilled from a large central platform, the wells are drilled from subsea clusters. For these types of wells, the wellhead and Christmas tree is installed directly on the seabed, with production from several wells co-mingled at a subsea manifold. Subsea manifolds are often linked by pipelines and umbilical control lines back to a nearby platform, where engineers can control and monitor the oil and gas production.

Drilling grinds up the rock into tea-leaf-sized cuttings which are brought to the surface by the drilling mud. The drilling mud is passed over a shale shaker which sieves out the cuttings. 

Data logging

Vital information – data logging – on the type of rock drilled and the fluids it contains often needs to be obtained either while actually drilling, or before casing. This is obtained by running electronic measuring devices into the well – either while drilling (as part of the drill-string) or after drilling on ‘wireline'. The various types of measurement include: electrical resistivity of fluids within the rock; the speed of sound through the rock; reaction of the rock to gamma ray bombardment; production of gamma rays from fluids within the rock due to neutron bombardment; and natural gamma radiation of the rocks. The data obtained gives an indication of rock type and porosity and the presence of oil or gas.

This is another crucial technology area supported by Premier, with recently enhanced process capabilities allowing the St-Albans-based company to offer tightly toleranced drilled holes up to 4m deep through the difficult to cut materials used, such as super duplex stainless steel.

“Our recent investment in a large ejector drilling machine allows us to machine the larger components used in the offshore industry, such as well head parts up to 4m long. And, we have increased our CNC machining capacity up to 4m to support this extension of our capabilities,” Mr Grant concludes. Drilling fluid (also called mud), which is mainly water-based, is pumped continuously down the drill-string while drilling. It lubricates the drilling tools, washes up rock cuttings and most importantly, balances the pressure of fluids in the rock formations below to prevent blowouts.

Premier
www.premier-drilling.co.uk