Oil and Gas Production Basics (Part 1)

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In this part, we will talk about the ff:

– Definition and overview of oil and gas production

– Different onshore and offshore production facilities

Definition

Production is the operation that brings hydrocarbons to the surface and prepares them for processing. Production begins after the well is drilled. The mixture of oil, gas and water from the well is separated on the surface. The water is disposed of and the oil and gas are treated, measured, and tested. Production operations include bringing the oil and gas to the surface, maintaining production, and purifying, measuring, and testing.

Exploration

Initial activities for oil and gas companies include exploration. In the past, surface features such as tar seeps or gas pockets provide clues to the location of shallow hydrocarbon deposits. Today, a series of surveys, starting with geological mapping through advanced methods such as seismic, magnetic and gravity surveys provide analysis data that identify potential hydrocarbon bearing rock as prospects.

Drilling is part of the exploration stage. The oil and gas companies analyze the reservoir prospects further by measuring their production capacities. Once their analysis shows good source of oil and gas, they drill a well into the reservoir.

 

Overview of an Oil and Gas Production Facility

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1  Onshore well

2  Offshore, fixed multi platforms

3  Offshore, fixed, self-contained platforms

4  Offshore, self-contained, concrete gravity platforms

5  Offshore, floating, single-point mooring

6  Storage/shuttle tanker

7  Offshore, floating, tension leg platforms

8  Subsea manifolds

 

Overview of Processing Systems in an Oil and Gas Production Facility

 

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At the left side of the diagram are the wellheads. These are part of the gathering system. The wellheads feed into the manifolds. The rest of the diagram is the actual process, often called the gas oil separation plant (GOSP). More often, the well-stream will consist of a full range of hydrocarbons from crude oil, gas (methane, butane, propane, etc.) to condensates (medium density hydrocarbons). With this well flow, we also get a variety of unwanted components, such as water, carbon dioxide, salts, sulfur and sand. The purpose of the GOSP is to process the well flow into clean, marketable products: oil, natural gas or condensates. Also included are a number of utility systems, which are not part of the actual process but provide energy, water, air or some other utility to the plant.

 

ONSHORE

3As the name implies, onshore pertains to the oil and gas production facility located on land. The sources of oil and gas for onshore facilities are thru wells.

The equipment shown on the picture is a sucker rod pump which is used to extract oil from a well.

For small reservoirs, oil is simply collected in a holding tank and picked up at regular intervals by tanker truck or railcar to be processed at a refinery.

For wells in oil-rich areas with high capacity, the product is sent thru pipeline. The production may come from different license owners, thus metering of individual well-streams is an important task.

Unconventional forms of oil 5have come into play in the market. These are oil sands and shale oil. Higher oil prices and new technology enabled unconventional oil to be profitably extracted and processed. Oil sands or technically called bituminous sands have been found in extremely large quantities in Canada, Kazakhstan and Russia. Steam injection is used to extract the oil sands. It must be further processed to separate the bitumen from the sand.

Shale oil, on the other hand, is produced from oil shale rock fragments thru the process of pyrolysis, hydrogenation, or thermal dissolution. This process converts the organic matter within the rock into synthetic oil and gas. The largest reserves of shale oil is in the United States. The leading producers were China, Estonia and Brazil.

 

OFFSHORE

A whole range of different structures is used offshore, depending on size and water depth. Some of the common offshore structures are:

 

Shallow Water Complex6

This is characterized by several independent platforms with different parts of the process and utilities linked with gangway bridges. Individual platforms include wellhead riser, processing, accommodation and power generation platforms.

Gravity Base

This consists of enormous concrete fixed structures placed on the bottom, typically with oil storage cells in a “skirt” that rests on the sea bottom. The large deck receives all parts of the process and utilities in large modules. Large fields at 100 to 500 meters of water depth were typical in the 1980s and 1990s. The concrete was poured at an onshore location, with enough air in the storage cells to keep the structure floating until tow-out and lowering onto the seabed.

Fixed Platform8

This consists of a jacket (a tall vertical section made of tubular steel members supported by piles driven into the seabed) with a deck placed on top, providing space for crew quarters, a drilling rig, and production facilities. The fixed platform is economically feasible for installation in water depths up to 1,500 feet.

Compliant Tower

This is much like a fixed platform. It consists of a narrow tower, attached to a foundation on the seafloor and extending up to the platform. This tower is flexible, as opposed to the relatively rigid legs of a fixed platform. Flexibility allows it to operate in much deeper water, as it can absorb much of the pressure exerted by the wind and sea. Compliant towers are used between 500 and 1,000 meters of water depth.

 

Floating Production

Floating production is where all topside systems are located on a floating structure with dry or subsea wells. Some common floaters are:

a) Floating Production, Storage and Offloading (FPSO)

b) Tension Leg Platform (TLP)

c) Semi-submersible platforms

d) SPAR

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a) Floating Production, Storage and Offloading (FPSO)

An FPSO is typically a tanker type hull or barge with wellheads on a turret that the ship can rotate freely around (to point into wind, waves or current). The turret has wire rope and chain connections to several anchors (position mooring POSMOOR), or it can be dynamically positioned using thrusters (dynamic positioning DYNPOS). Most installations use subsea wells. The main process is placed on the deck, while the hull is used for storage and offloading to a shuttle tanker. It may also be used for the transportation of pipelines.

 

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b) Tension Leg Platform (TLP)

A Tension Leg Platform (TLP) consists of a structure held in place by vertical tendons connected to the sea floor by pile-secured templates. The structure is held in a fixed position by tensioned tendons, which provide for use of the TLP in a broad water depth range up to about 2,000m. The tendons are constructed as hollow high tensile strength steel pipes that carry the spare buoyancy of the structure and ensure limited vertical motion.

 

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c) Semi-submersible platforms

Semi-submersible platforms have a similar design but without taut mooring. This permits more lateral and vertical motion and is generally used with flexible risers and subsea wells. Similarly, Seastar platforms are miniature floating tension leg platforms, much like the semi-submersible type, with tensioned tendons.

 

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d) SPAR

The SPAR consists of a single tall floating cylindrical hull, supporting a fixed deck. The cylinder does not, however, extend all the way to the seabed. Rather, it is tethered to the bottom by a series of cables and lines. The large cylinder serves to stabilize the platform in the water, and allows for movement to absorb the force of potential hurricanes. SPARs can be quite large and are used for water depths from 300 up to 3,000 meters. SPAR is not an acronym, and is named for its resemblance to a ship’s spar. SPARs can support dry completion wells, but are more often used with subsea wells.

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Subsea Production Systems

Subsea production systems are wells located on the sea floor, as opposed to the surface. As in a floating production system, the petroleum is extracted at the seabed, and is then “tied-back” to a pre-existing production platform or even an onshore facility, limited by horizontal distance or “offset.” The well is drilled by a movable rig and the extracted oil and natural gas is transported by undersea pipeline and riser to a processing facility. This allows one strategically placed production platform to service many wells over a reasonably large area. Subsea systems are typically used at depths of 7,000 feet or more and do not have the ability to drill, only to extract and transport. Drilling and completion is performed from a surface rig. Horizontal offsets of up to 250 kilometers/150 miles are currently possible.

 

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The next part will be about Upstream Process Section, please stay tuned.

Thank you for reading! If you have learned something today, please do us a favor and share this with your colleagues and friends. For any feedback, please leave a comment below. We would love to know what you think about this article and hear it directly from our readers.

Maraming Salamat po!

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