Subsea Oil and Gas
Petroleum is a fossil fuel that includes all liquid, gaseous, and solid hydrocarbons. Petroleum is discovered in the Earth’s crust in porous rock formations. Huge amounts of oil and gas have been extracted in recent years from “tight” rock formations such as shale. The world’s second largest oil reservoir is the Athabasca tar sands in Alberta, Canada. Oil has become the world’s primary energy source due to its high energy density, ease of transport, and relative availability. Petroleum is also utilized in the production of pharmaceuticals, solvents, fertilizers, pesticides, and polymers.
Petroleum has been in use since prehistoric times. Babylon’s walls and towers were built with asphalt extracted from oil mines along the banks of the Issus River, a tributary of the Euphrates. In ancient Persia, petroleum was also used for medicine and illumination. Bamboo-drilled wells were producing oil in China by 347 AD.
Abraham Gessner of Nova Scotia, Canada, devised a method to produce kerosene from coal in 1846. The first large refinery was created in Ploesti, Romania, in 1856, using indigenous oil. Edwin Drake’s Titusville, Pennsylvania, well in 1859 is commonly considered as the first modern oil well. Drake’s well was drilled rather than dug, was driven by a steam engine, and was sponsored by a company, and it resulted in the first substantial oil boom. From then on, “rock oil” began to supersede whale oil as the primary source of light fuel. In the 1800s, liquefied petroleum gas (LPG) was developed. In the early twentieth century, the internal combustion engine and its development into cars created a need for gasoline. This accelerated the industry’s expansion.
The widespread use of natural gas as a fuel is novel. Crude oil is produced by an oil well. However, dissolved gas is released when crude oil is brought to the surface and exposed to reduced pressure. Due to its lower density, a “cap” of natural gas may float above the oil depending on the reservoir. Historically, there was less gas infrastructure, and gas was considered an annoyance. What couldn’t be used to power machinery was either buried or flared off (burned). Natural gas has become an important source of heating and electricity generation due to its extensive infrastructure.
Oil and gas account for more than 60% of total energy consumption in the United States, with oil used for transportation and gas used for electricity generation. Oil and gas, like all fossil fuels, are nonrenewable energy sources with finite supplies, according to experts. However, technology has always played an important role in oil and gas exploration. Supply and demand determine oil and gas prices, and as prices rise, so do technological innovations. This has enabled the United States and the rest of the world to constantly seek out and exploit new sources of oil and gas to replenish those that have been depleted over time.
There are numerous inland and offshore oil and gas fields around the world, and the term subsea refers to the exploration, drilling, and development of these fields. Underwater oil fields and infrastructure are referred to as subsea wells, subsea fields, subsea projects, and subsea developments.
There are two types of subsea oil field development: shallow water and deep water. When bottom-based facilities such as jack up drilling rigs and permanent offshore structures are used, saturation diving is possible at shallow water depths. Deepwater refers to offshore operations that necessitate the use of floating drilling boats and floating oil platforms, as well as remotely operated underwater vehicles (ROVs), because human diving is impractical.
The first subsea completion took place in Lake Erie in 1943, in 35 feet (11 meters) of water. Diver intervention was necessary for the installation, maintenance, and flow line connections of a land-type Christmas tree. In 1961, Shell drilled their first subsea well.
They were intended for use at depths of up to a few hundred meters. In the intervening years, technology has advanced to allow for deep-water production, and the industry is constantly expanding its reach through the use of fixed platforms, compliant towers, SPAR (single point anchor reservoir), and FPSOs (Floating Production Storage Offloading).
A subsea development is an oil or gas field that is located on the seafloor. Semi-submersible mobile drilling rigs are used to drill wells from the water’s surface. A “wet tree” is then used to seal the wells on the seafloor. Most subsea systems use underwater flowlines to transport production to a surface processing system. A simple subsea system consists of a single well that feeds a nearby platform. Multiple wells flow through a subsea manifold and then to a production plant, which could be offshore or onshore. Figure 1 displays a number of subsea production components that are coupled to floating facilities.
Total field development expenses are reduced because an existing platform may be used for production or a dedicated platform can be located in shallower water.
The first underwater completion occurred in Lake Erie in 1943, at a depth of 35 feet. In 1961, Shell built the first subsea well off the coast of California. Companies focused on fixed platform technology with dry trees after initially showing interest in California and the Gulf of Mexico. During that time, Norway advanced subsea technology, beginning with the 1982 Frigg field in the North Sea and continuing for decades. Oil companies, particularly Shell USA and Petrobras Brazil, continued to develop subsea systems for deep-water applications. Shell’s Mensa field in the US Gulf of Mexico began producing in 5,376 feet of water in July 1997, breaking the previous record. Shell’s Tobago project in the Gulf of Mexico is the deepest subsea development at the moment.
Operators are now placing processing equipment on the seafloor thanks to advancements in subsea technology. Gas-liquid separation, electrical submersible pumps, and sand management are examples of technologies. The development of process technology is centered on oil-water separation and subsea produced water disposal. To extract offshore reserves, topside equipment (pump, separator, water handling, compressors, processing, and storage) is used. Surface facilities are expensive, and space in deep or remote waters is limited, making production difficult.
Production risers, flow lines, and associated production control systems comprise the subsea production system. A subsea production system manages fluid production and transportation, enabling for the exploitation of remote and/or deep-water deposits by installing wellheads and associated mechanical and electrical equipment on the seafloor.
Surface or shore infrastructure can be linked to subsea wells. Modularized subsea technology can improve recovery factors by lowering well backpressures while also cutting development and production expenses (e.g. via multiphase pumping or subsea separation). Subsea technology is gaining traction in West Africa, Brazil, and Asia.
The oil industry has been able to develop reserves in greener areas and water depths down to over 3000 meters by moving from dry land to shallow-water areas via wellhead platforms, and then into deeper water depths of a few hundred meters. Improved subsea solutions, such as better drilling equipment, installation technologies, and control systems, are required to meet increasing criteria. As new technologies enable the design and installation of more advanced subsea systems, the subsea industry is undergoing a transformation. Subsea processing units, for example, can use pumps or compressors to separate different fluid phases and boost the fluids (subsea factory).
Small fields are linked to bigger facilities and field centers by subsea plants. Subsea technology extends the life of existing platforms and infrastructure, allowing for greater extraction of resources from the field. Advances in subsea technology allow for development in ultra-deep seas. Subsea plants can be linked to onshore processing facilities in no-frills areas. Production can be managed on the ground or through linked-in installations. Extreme weather rarely has an impact on the amenities.
Subsea technology enables more environmentally friendly offshore development and operations. Reduced ship and helicopter traffic during operations lowers emissions, while remotely controlled technology lowers high-risk activities