Saurabh SharmaBack in 1891, in Grand Lake St. Mary’s in Ohio, the first sets of submerged oil wells were drilled, with platforms built on piles. Ever since then, mankind has come a long way in terms of offshore drilling. Initially, wells were scarce, as suitable technologies and facilities were not available for successful, commercial deep-water drilling. Currently, drilling at very high depths of 3000 ft. below the surface of the earth is a feasible prospect, thanks to technological advancements in the oil & gas industry.
Offshore drilling refers to drilling under the seabed for existing hydrocarbons, which have been detected by advanced methods, such as the less reliable gravity metering and more reliable magnetic surveying and seismic surveying. Oil and natural gas get trapped in pockets below the seabed. To extract oil and gas from these deposits under the sea, oil drills are mounted over a platform, known as a drilling rig. In the recent times, oil & gas companies have been employing innovative methods, such as floating and fixed platforms, which support drilling right from the bed of the ocean. Offshore rigs can be differentiated based on their mobility and the depth at which drilling has to be carried out.
Classification of oil rigs
The image below represents the classification of rigs, with their operational depths.
- Drillship
- Semi-submersible
- Jack-up Rig
- Drilling Barge
- Land rig
While bottom-supported rigs maintain contact with the seafloor, floating units do not come in direct contact, but float on the water. A few of these are anchored to seafloor and partially submerged, and firms could also employ drilling ships that drill at varying depths. A Floating Production Storage and Offloading (FPSO) is one such floating rig that processes hydrocarbons, water, and gases. The concept of FPSO allows oil & gas companies to produce oil in deeper, remote areas, without the restrictions posed by fixed structures and technology. Due to its storage capacity for treated crude oil, on-board systems can also be powered. The treated oil is then transferred to shuttle tankers for shipment to refineries, by means of an offloading system. This has reduced the need for pipelines required to transfer oil to shores.
Risks associated with deep-water drilling
Due to the extremely high depths at which onshore drilling takes place, the offshore drilling market is usually considered to be less volatile than onshore drilling. Offshore rigs take longer to drill, and hence, drilling contracts are for longer periods of time. However, it is important to note that deeper the location of the rig, the riskier the venture is. Drilling in deeper waters is more complex and expensive. Moreover, the unpredictable marine weather adds to the woes of the contractor/company working for the deep and ultra-deep water E&P projects.
Directional drilling in the oil & gas industry
Although the concept of directional drilling was initially introduced in the late 1920s, it wasn’t until the 1930s that wells could be directionally drilled to tap into oil pockets. This process paved the way to access oil pockets that would have been otherwise inaccessible, due to their inclined deviation from usual standards. As an early example, the actual onshore rig was directionally drilled, into the offshore oil deposit. This form of drilling is common in the offshore operations of oil and gas companies.
Placing a rig for the production of oil and gas onto a remote offshore location requires the investment of significant capital. Hence, a more cost-effective method is to lay wells in a common area. Usually, this is not the case and directional drilling plays an important role in overcoming this issue. Instead of having multiple rigs for each cluster of wells, all well heads can be located on one platform, connected by a network of drilling pipes.
Platforms are one of the most expensively built structures in the world, incurring costs of billions of dollars. For such erections to exist, it is crucial to drill as many wells from this one location, as is environmentally possible. Directional drilling has made it possible to develop many sub-sea production levels using economic methods.
Types of directional drilling methods
Horizontal Drilling: This type of directional drilling finds applications in fractured reservoirs and reservoirs with low permeability rates for production in thin oil zones. It can also be used to increase production and efficiency of reservoirs, which are being drained by vertical wells. This method has also led to the innovative fracking technology, a method that enables oil & gas companies to extract oil from previously inaccessible shale rock formations.
Multilateral Drilling: This type of drilling refers to the addition of multiple wellbores in one reservoir, as shown in the figure below. Multilateral drilling can have a simple structure of an open hole with multiple sidetracks, or a complicated junction with controlled pressure and the option for re-drilling. This process is implemented where production cost can be minimized, while still increasing production incrementally. With limited spots out in the sea, this application is limited to offshore production. Another use is to introduce additional horizontal wells in a reservoir.
Sidetracking: One of the primary uses of directional drilling, this method is used to deflect the borehole by starting a new hole, above the bottom of the initial hole. It is generally employed as a tactic to bypass an already dysfunctional hole, or to have a better production formation by means of intersection, to attain a favourable position, in case of oil-water contact. Used in case of water or gas coning, it can also be used used to make an old well more productive. This is done by moving the bottom of an already existing hole from a depleted portion of the reservoir to a part with better output. If the platform incurs a huge cost, sidetracking and directional drilling can be used for multiple exploration of an area. In horizontal wells, it is common to sidetrack existing vertical wells. Multiple sidetracks drilled from the same well are called multilaterals.
The vital role played by petroleum and petroleum-based products in our daily lives cannot be stressed enough. The latest technologies have empowered organizations with the necessary ways and means to explore in depths unheard of. As the oil & gas business continues to reach new heights and witness fluctuations in market scenarios, the need of the hour is to bolster sustainability and productivity without causing ecological damages. Firms are therefore taking up active measures to protect the environment, by utilizing innovative technologies in offshore and onshore drilling activities.
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