EnergyBC

Production

Facilities - (For details see UKOOA Offshore Site and CFE Brochure)

If a well receives the green light for production, the next stage involves maximizing the recovery of all hydrocarbons and transporting them safely to shore where they await the market. In offshore environments, this involves the construction of large production platforms (rigs) capable of supporting hundreds of workers for long periods of time. Depending on the location, type of reservoir and expected life span of the platform, drilling and production platforms may or may not be incorporated into the same structure. These structures can cost billions of dollars to build and operate, and perform several functions in addition to drilling and extracting hydrocarbons. Once oil and gas are collected, they must be treated before transport. Raw crude oil is a hot, corrosive, high pressure fluid mixed with gas, water and sand, all of which must be separated out. The rig also process all wastes generated by the drilling and treats them prior to ultimate disposal to minimize their environmental impact.

Most oil and gas production platforms in offshore Britain and Nova Scotia rest on steel supports known as "jackets", a term derived from the Gulf of Mexico. The steel jacket, fabricated from welded pipe, is pinned to the sea floor with steel piles. Above it are prefabricated units or modules providing accommodation and housing various facilities including gas turbine generating sets. Towering above the modules are the drilling rig derrick (two on some platforms), the flare stack and service cranes. Horizontal surfaces are taken up by store areas, drilling pipe deck and the vital helicopter pad.

In Newfoundland, the Hibernia platform is fabricated from concrete. Concrete gravity platforms are held firmly to the seabed by their great weight. The Hibernia structure is 224 meters tall and weighs 1.2 million tonnes. This type of structure was selected because it can handle extreme storm conditions, sea ice and icebergs. The Hibernia platform is designed to withstand an encounter with a six-million-tonne iceberg. Several platforms may have to be installed to exploit larger fields, but where the capacity of an existing platform permits, subsea collecting systems linked to it by pipelines that have been developed using modern technology. These will get increasing use as smaller fields are developed.

Alternatively, a subsea collection system may be linked via a production riser to a Floating, Production, Storage and Offloading (FSPO) vessel. FPSOs can offer significant advantages over fixed production platforms, particularly in remote offshore locations where deep water, strong ocean currents and harsh weather conditions may occur, or where export pipelines are difficult to install or uneconomic to run. They can also be floated off at the end of a field's productive life and re-used elsewhere, which has environmental as well as economic benefits, particularly for marginal fields where the production facilities may only be required for a few years.

The $2-billion Sable Island Offshore Energy Project in Nova Scotia began producing natural gas and natural gas liquids in late 1999 using FPSO vessels to retrieve the crude oil. This FPSO vessel is a ship-shaped production platform with integrated oil storage from which oil is offloaded to a shuttle tanker. One of the largest such vessels ever built, the Terra Nova FPSO is 292.2 metres long. The vessel can store 152,600 cubic metres of crude oil and can accommodate up to 80 personnel. Oil production wells were pre-drilled by a semi-submersible drilling platform. The wellheads and production manifolds are placed in "glory holes" – excavations in the sea floor – that protect the equipment from scouring icebergs. A network of more than 40 kilometres of flexible flowline is used to convey hydrocarbons to and from the wells. Produced gases are separated from the oil and re-injected into the reservoir for possible future extraction.

The specific employment opportunities associated with production facilities are in offshore production operations, marine and air support and shore-based support and administration. By way of example, the Terra Nova FPSO vessel has 90 to 100 crew, half of whom will be working offshore at any time. Typical skill requirements includes deck officers, seamen, deckhands, maintenance personnel, mechanics, electricians, control room operators, loss prevention personnel, crane operators, catering personnel, radio operators, medics and environmental and forecasting specialists. Marine and air support totals 60 to 80 people and includes the crew of supply and support vessels and helicopters. There are 45 to 50 onshore personnel, including office staff, engineers, geologists, geophysicists, technicians, yard and dock workers and marine operations specialists. (Petro-Canada 1997) (JWEL, 2001)

TWO STAGES OF RECOVERY (CFE Brochure)

Primary Recovery

Producing crude oil and natural gas from offshore locations is similar to the process used onshore. Crude oil and natural gas wells are prepared for production through a process called "completion". In the first step, a production casing is cemented into the well bore. The casing – tubular steel pipe connected by threads and couplings – lines the total length of the well bore to ensure safe control of the crude oil and natural gas, prevent water entering the well bore and keep rock from sloughing into the well bore.

Once the cement has set, the production tubing can be put in place. Production tubing is steel pipe that is smaller in diameter than the production casing. Production tubing in most offshore wells today consists of coiled tubing, a continuous, high-pressure-rated hollow steel cylinder. Production tubing is lowered into the casing and hangs from a sea floor installation called the wellhead. The wellhead has remotely operated valves and chokes that allow it to regulate the flow of oil and gas. The casing is then perforated to allow crude oil and natural gas to flow into the well based on pressure differentials between the well and surrounding rock. This is done with a perforating gun, an arrow of shaped explosive charges that is lowered into the well. An electrical impulse fires the charges that perforate the casing, surrounding cement and reservoir rock.

The primary recovery stage is the flowing of crude oil and natural gas into the well on its own. It flows because, as mentioned above, the pressure is higher outside the well than it is inside.

Secondary Recovery

Natural gas flows to the surface under its own pressure. After primary recovery, additional oil may be brought to the surface by pumping fluid back into the reservoir rock during the later stages of a well’s life span. In both oil and gas wells, recovery can also be enhanced by increasing the porosity or permeability of a formation through physical or chemical means. The two most common methods are acidizing and fracturing (also known as“fracing”). Acidizing involves injecting acids under pressure through the production tubing and perforations and into the formation. This procedure creates channels beyond the perforations that allow crude oil and natural gas to flow back to the well. Fracing involves pumping a fluid, such as a water gel, down the hole under sufficient pressure to create cracks in the formation. Whether these techniques are used depends on a number of factors, including potential environmental impacts as well as the geology of the reservoir.

Transport

In situations where an FPSO is not employed, hydrocarbons are usually stored in large tanks on the production platform until they are transported to land either by pipelines or tanker ships. Pipelines are often used for oil when the distance from the rig to shore is relatively short, and are also favored in situations where natural gas is the main product from a reservoir. In most other cases, tanker ships ranging from small cargo vessels to super tankers capable of carrying millions of litres of oil are used. All of these ships have double-hulled, double-bottomed construction, to maximize the safety and containment of such large quantities. Once the oil or gas reaches the shore, it is refined once again to produce commercially viable products (e.g. gasoline, petrochemicals).

Both Hibernia and Terra Nova include crude oil storage facilities onboard the production platforms. Shuttle tankers, specially designed for use in the waters off Newfoundland and Labrador, carry the crude oil from the platforms directly to market or to a transshipment terminal at Whiffen Head, Newfoundland and Labrador, for storage and transshipment to tankers that carry the oil to refineries.

Natural gas from the Sable Offshore Energy Project is gathered at the Thebaud production platform and compressed for shipment. It is shipped through a subsea pipeline to the onshore natural gas processing plant, where unwanted substances such as water vapour and natural gas liquids such as propane, butane and pentanes are removed. The liquids go to another plant for separation, storage and marketing. The dry natural gas from the processing plant is compressed and shipped via pipeline (such as the TransAlaska Pipeline pictured to the right) to industrial customers and natural gas distribution utilities in Atlantic Canada and the New England states.

Some credit from above text to Canada's Evolving Offshore Oil and Gas Industry by the Canadian Center for Energy Information, 2004 and UKOOA - The UK's Offshore Oil and Gas Web Site, 2004