What they do for oil production. How oil is produced at sea: how an offshore oil platform is created and operates. Development of oil fields - preparation and drilling process
Vladimir Khomutko
Reading time: 4 minutes
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World map oil fields is quite large, but everywhere the process of oil and gas production takes place with the help of wells that are drilled in the strata of rocks with the help of drilling rigs. They are familiar to many from the movies, in which they showed lattice cone-shaped "oil rigs". These are the drilling rigs, which, after the wells are organized, are dismantled and transported to another place.
The places where such production takes place are called industries or deposits. Transportation of oil and gas from oil fields to refineries engaged in the production of commercial oil products is carried out through pipelines.
Drilling a well can take several days or even several months.
Oil and gas wells- not just holes in rocks. Their shaft is cased from the inside with special pipes made of steel, called tubing (tubing). It is through them that hydrocarbons are extracted to the surface.
Outside, the main tubing string, called the production tubing, is cased with other casing pipes, which reinforce the wellbore and isolate the various earth formations from each other. The length of the shaft of such a development can reach several kilometers.
To prevent different rock formations from communicating with each other, the free space behind the casing pipes is usually cemented. This makes it possible to prevent interstratal circulation of water, gases and oil itself.
The cement ring, arranged behind the casing strings, collapses over time due to physical and chemical influences, as a result of which there is annular circulation. This phenomenon negatively affects the production of black gold, since in this case, in addition to the necessary oil, gases or water from adjacent rock layers enter the wellbore from the reservoir, which is called a reservoir, and their amount often exceeds the volume of the crude oil itself.
In order for the produced resource to enter the wellbore at all, it is necessary to punch holes in the casing and the cement layer behind it, since both the casing and cement isolate the reservoir from the well. Such holes are made with the help of special shaped charges, which pierce not only cement and casing pipes, but also form holes in the oil reservoir itself. This process is called perforation.
Oil production methods are different, and depend on the pressure in the reservoir. Oil production is carried out using various technologies. Oil can flow on its own, in other words, it can rise up the wellbore from the reservoir to the surface without the help of pumping equipment, due to its low density.
If oil is produced without the use of additional pumping equipment, then this method of oil production is called fountain.
The essence of the flowing process is that the hydrostatic (water) pressure in the reservoir at a depth is quite high (for example, at two kilometers it will be about 200 atmospheres). This indicator is called reservoir pressure.
Since the density of oil and gas is less than that of water, then at the same depth the pressure in the wellbore, which is called bottomhole, will be (with a density of raw materials about 800 kilograms per cubic meter) about 160 atmospheres. As a result of the resulting depression (pressure drop) between the productive formation and the wellbore, oil rises upward.
In addition, oils, as a rule, contain light hydrocarbon compounds, which, in the event of a decrease in pressure, become gaseous (gases dissolved in the oil mixture). The release of such gases further reduces the density of the extracted raw materials, as a result of which the depression described above increases. This process can be compared to opening a warm bottle of champagne, from which a powerful sparkling fountain comes out.
The amount of raw materials received from the well per day is called by experts the well flow rate (not to be confused with the accounting term "debit"). Gradually, especially with intensive production, the reservoir pressure in the reservoir decreases, obeying the law of conservation of energy. As a result, the flow rate of the well decreases, since the pressure drop between the formation and the borehole becomes insignificant.
To increase the in-situ pressure, water is pumped into the reservoir from the surface using injection wells.
In some types of reservoirs, in addition to oil, there is immediately a large volume of formation water, due to the expansion of which, the drop in in-situ pressure is partially compensated, and the need for additional water injection may not arise.
In any case, water gradually seeps into the developed oil-saturated layers of the reservoir, and through them into the wells themselves. This process is called flooding, which also causes a decrease in production. This is explained not only by a reduction in the proportion of oil itself in the produced mixture, but also by an increase in the density of the watered oil mixture. The bottomhole pressure in mine workings with a high degree of water cut increases, which leads to a decrease in drawdown. Eventually, the well stops flowing.
In other words, the flow rate of any well is gradually decreasing. As a rule, the maximum value of this parameter is reached at the very beginning of reservoir development, and then, as oil reserves are depleted, the flow rate decreases, and the more intensive oil production occurs, the faster this decrease is. In other words, the higher the initial flow rate, the faster it will fall.
In order to return the well to its previous productivity, various works are carried out at the wells in order to intensify production. Carrying out such works, as a rule, leads to an instant increase in production, but after that they begin to fall at a faster pace. On Russian oil wells ah, the rate of decline in production rate ranges from 10 to 30 percent per year.
To increase the flow rate of production wells with either a high degree of water cut, or with reservoir pressure falling below the prescribed level, or with a low level of concentration of dissolved gases, various technologies of the so-called artificial oil production are used. And the main such methods are techniques with the use of pumps of various types, the production of which is currently very developed.
The most widespread are the well-known "pumping units", which are called sucker rod pumps (abbreviated - sucker rod pumps). Electrically driven centrifugal pumps (abbreviated as ESP), which are not visible on the surface, are also quite common. The main oil production in the Russian Federation is currently carried out with the use of ESP.
The principle of operation of all pumping production methods is based on a decrease in the pressure value in the bottomhole, as a result of which the drawdown increases and, as a result, the flow rate.
The mechanized technological process is not the only way out in the event of an artificial increase in well productivity.
For example, the so-called hydraulic fracturing or gas-lift technique is often used, but these are topics for separate articles.
Oil fields can be developed both at high bottomhole pressures and at low ones. If the bottomhole pressure is high, then the depression decreases, the flow rate decreases, and although reserves are produced, but at a slow pace. If, on the contrary, the bottomhole pressure is low, then the depression increases and the flow rates increase significantly, which leads to high rates of production of raw materials reserves.
Some features of the oil industry
Often, with a high intensity of field development, the term "predatory exploitation" or "predatory prey" is used, which have a pronounced negative connotation... At the same time, it was assumed that with such well operation oil companies representatives of the oil industry, as it were, “skimmed the cream” from the fields being developed, or extracted readily available raw materials, and the rest of the reserves were simply thrown away, in which case the remaining oil was no longer possible to raise to the surface.
In most cases, this statement is incorrect. In most of the oil fields, residual hydrocarbon reserves do not in any way depend on the intensity of their production. As proof, one can cite the fact that a sharp increase in the amount of Russian oil produced occurred in the late twentieth and early twenty-first centuries, but seventeen years have passed since then, and the volumes of domestic oil produced do not even think about decreasing (the level of 2015, by for example, compare with the level of 2000).
And this period for oil fields is quite long. In this regard, if the rate of development of oil reserves would lead to the loss of raw materials remaining in the reservoirs, then the volumes have long begun to decrease, but this is not happening.
High production intensity increases the risks associated with the possibility of emergencies, for example, due to the destruction of the cement layer around the wellbore, which leads to unwanted circulation in the annulus and to premature breakthroughs of formation water. However, in the general case, such a production regime is almost always economically justified, and at almost any level of oil prices. For an illustrative example, you can compare this with a traffic situation.
If, for example, the speed of cars outside the city is limited to twenty kilometers per hour, and then using draconian measures to force this limitation to be strictly observed, then with a high degree of probability the number of accidents will be minimal (if any). But why then will these roads be needed from an economic point of view?
As we said earlier, the increase in the intensity of Russian oil production occurred at the turn of the twentieth and twenty-first centuries.
In most cases, production was carried out by reducing the pressure in the bottom hole (respectively, increasing the drawdown) in the producing wells. To do this, pumps were lowered into the gushing workings, and the wells, on which pumping equipment had already been installed, was replaced with a more efficient one.
And there was nothing unambiguously bad in this and there is not, neither from a technical nor from an economic point of view. TO negative consequences such a method of extraction can be attributed only to strategic factor, since an increase in depression, although it leads to an increase in the rate of oil production, on the other hand, accelerates the decline in production rates in already drilled productive areas.
Since the flow rates of oil wells are constantly falling, in order to maintain oil production at a certain level, it becomes necessary to drill new wells, and the faster the flow rates fall, the more such mine workings must be drilled every year. In other words, intensive production makes it more difficult to maintain a certain constant volume of oil production every year.
On the other hand, if wells operation does not differ in intensity (due to high bottomhole pressure), then for such fields there is an opportunity to increase production volumes at the right time (with the help of different ways reducing the pressure in the bottom hole). This is exactly how the volume of extracted raw materials is regulated in Saudi Arabia and Kuwait. In this regard, from a strategic point of view, a low intensity of oil production is safer.
Oil has been known to man since ancient times. People have long noticed the black liquid oozing from the ground. There is evidence that already 6500 years ago, people who lived in the territory of modern Iraq, added oil to building and cementing materials when building houses in order to protect their homes from moisture penetration. The ancient Egyptians collected oil from the surface of the water and used it in construction and for lighting. Oil has also been used to seal boats and how component mummifying substance.
Not everywhere oil was collected only from the surface. In China, over 2,000 years ago, small boreholes were drilled using metal-tipped bamboo trunks. The wells were originally intended for the production of salt water, from which the salt was extracted. But when drilling to a greater depth, oil and gas were extracted from the wells.
Although, as we can see, oil has been known since ancient times, it found rather limited applications. The modern history of oil begins in 1853, when Polish chemist Ignatius Lukasiewicz invented a safe and easy-to-handle kerosene lamp. According to some sources, he also discovered a way to extract kerosene from oil on an industrial scale and in 1856 founded an oil refinery in the vicinity of the Polish city of Ulaszowice.
Back in 1846, Canadian chemist Abraham Gesner figured out how to get kerosene from coal. But oil made it possible to obtain cheaper kerosene and in much larger quantities. The growing demand for kerosene used for lighting has generated a demand for the starting material. This was the beginning of the oil industry.
According to some sources, the world's first oil well was drilled in 1847 near the city of Baku on the shores of the Caspian Sea. Soon after that, so many oil wells were drilled in Baku, then part of the Russian Empire, that they began to call it the Black City.
However, the birth of the Russian oil industry it is considered to be 1864. In the fall of 1864, in the Kuban region, a transition was made from the manual method of drilling oil wells to a mechanical percussion rod using a steam engine as a drive for a drilling rig. The transition to this method of drilling oil wells confirmed its high efficiency on February 3, 1866, when the drilling of well 1 at the Kudakinskoye field was completed and an oil gusher came out of it. It was the first oil fountain in Russia and the Caucasus.
The date of the beginning of industrial world oil production, according to most sources, is considered to be August 27, 1859. This is the day when from the first oil well in the United States drilled by "Colonel" Edwin Drake, an inflow of oil with a fixed flow rate was received. The 21.2m deep well was drilled by Drake in Titusville, Pennsylvania, where water wells were often drilled with oil.
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The essence of LGBT people is that it is a bookmark by the powers that be. When it is necessary to reduce the population or keep it at the level, LGBT people are in vogue, and all their rights are violated. And when you need to increase the population, then they somehow subside ... Nobody squeals for their gay rights. It's just that Russia was more chaste than Europe and longer, as evidenced by the shock of the Germans when she raped our girls during the Second World War. Russia is needed both as a territory for the extraction of minerals, and as just a large part of the land with all that it implies. We could never be conquered by force. Now there are other methods. Information war. And she is very sophisticated. Wow, even enumerate how much evil can be done by instilling lies in people. From proper nutrition to the overthrow of power and TD, etc.
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Comment onEternity smells like oil.
Salute, guys! Today I will tell you about how oil is produced in Western Siberia. The same black gold, around which serious passions are simmering, on which the economy of our country stands, the dollar and the euro are "walking". In order to see the mining process (as people call it in the "topic"), I went to the Yuzhno-Priobskoye oil field and, using its example, will tell you how it was. Go!
1. Demonstrative bottling of oil.
It all starts with the fact that a company engaged in oil production uses special equipment, resorts to the help of geologists to discover a field. Then you need to understand how much oil is hidden in the layers of the earth, and in general, is it economically profitable to extract it? Soil studies are being carried out, a large number of "prospecting" wells are being made, and if a deposit is found and it will be useful, then a lot of development work has already begun. To do this, create a "cluster" - a platform that combines many drilled wells. The bottom of the well goes into the ground at an angle and reaches a couple of kilometers, at present they are drilled at an angle, and the drilled bottom may be at a distance of a kilometer from the bush.
The Priobskoye oil field is located in the Khanty-Mansiysk Autonomous Okrug, near Khanty-Mansiysk. It was discovered back in 1982, but development began recently, since earlier it was not only economically unprofitable, but also there were no technologies that would ensure the efficiency of the field. Geological reserves of subsoil are estimated at 5 billion tons. Proved and recoverable reserves are estimated at 2.4 billion tons. For example, in this area, oil deposits are located at a depth of 2.3-2.6 km.
2. Bush # 933. To get here, I had to issue all the passport data in advance, get a pass, put on overalls, without which they would not let me go anywhere, drive through the security cordon to the field, and also listen twice to safety instructions from several managers. Everything is extremely strict and you won't take an extra step to the side.
3. Briefing for all guests from the well drilling contractor. By the way, Gazpromneft-Khantos does not drill itself, it is done by contractors who win a tender and subsequently work at the facility.
4. To the right is a drilling rig, on top of which a winch with a huge hook is suspended, which is moved up and down by an electric motor. This design is called "top drive".
The first bit is lowered into the dug hole - a blank with three spiked rotating heads, which drills the ground. This bit is mounted on drill collars, which in turn are screwed onto conventional drill pipes. And these assembled "candles" screw 2-4 pieces together. This whole huge structure, called a drill string, is screwed onto an electric motor at the top, suspended from the same hook from above.
While drilling the well, the "top drive" rotates this entire structure and goes down, transferring the weight of the string to the bit. The weight of the drill string, hanging on the hook from above, goes down into the well and is about 130 tons. Descent and retrieval of the drill string occurs many times, so you have to replace the bit with a new one. Drilling fluid is pumped down the pipes at a pressure of ~ 100 atmospheres. This fluid passes inside the entire structure and exits through the bit, cooling it, and then returns upward through the space between the walls of the string and the walls of the well, lifting cuttings - drilled rock with it to the surface. By the way, a new technology is used at this field - horizontal drilling, that is, the chisel goes not only down, but also to the side.
5. Since the drilling of wells at the present time can be carried out not strictly vertically, but at any given angle, these numbers just mean the direction of the bit.
6. The solution raised upward is cleaned, and the cuttings are thrown into a special pit, which is reclaimed after drilling. Then vegetation is planted on top of the ground.
7. "Candles" are disassembled, but soon their turn will come to go deep underground.
8. Regularly a specialist takes a sample of oil to check its composition. Below you can see the glass bottles into which it is poured.
9. Journalists and bloggers, like children, consider an outlandish bottle of warm liquid. It smells of gray and oil, a kind of mixture with a mild, but odor.
10. The resulting oily liquid is dirty, earthy in color with bubbles and contains sand.
11. fotomanya
happy =)
12. Black gold looks like ordinary dirty water. Due to a complex technological process, oil, water and associated petroleum gas are released from this slurry.
13. The structure, called "Christmas tree", underneath it is a centrifugal electric pump, lowered to the bottom of the well, which pumps fluid to various treatment stations in order to obtain clean oil in the future. As you can see, there are no traditional "rockers" here, since they are ineffective and not profitable, roughly speaking - this is the last century.
14. After the well is ready, drilling rig on rails they are transported further to start the process of drilling a new well.
15. In the foreground, planned well workover is taking place. Moreover, such repairs are required for each of the wells after a certain period of time.
16. People of the heroic profession, not otherwise. In cold conditions, they repair the drilling and, judging by their faces, they like it!
18. The town of oil workers is located at a distance from the drilling rig, they have their own little life there. Here even the 3g Internet worked and you could post pictures!
19. Leaving well pad No. 933, arriving at production sites with oil treatment units and a workshop for preparing oil pumping. The site is located a few kilometers from the drilling site, where oil is supplied through pipes.
19. The oil treatment unit is designed to receive oil wells production, its preliminary separation into oil, associated petroleum gas and formation water and subsequent oil treatment to commercial quality. In addition, at the OTP, there is accounting for commercial oil, accounting and utilization of associated gas, pumping of commercial oil into the pipeline.
20. There are a lot of pipes, complex structures, where oil is processed for its further use.
21. The OTP includes a large number of elements, for example: separators, pumping units, drainage tanks, line heaters and other devices. the coolest diagram of how everything works. Personally, I don't understand everything, maybe one of you is an expert)
22. One of the huge reservoirs of water required for oil refining.
23. Eugene shows: - THERE IS OIL! Yes, these tanks hold ready-to-use oil.
24. Yuzhno-Priobskiy gas processing plant (GPP), at the opening of which (by teleconference) Dmitry Medvedev was a year ago.
25. The processing capacity of the gas processing plant will amount to 900 million cubic meters of associated petroleum gas per year. The APG utilization rate is 96%, which meets modern world requirements.
29. A huge automated plant, which is served by a small number of employees.
27. General manager"Yuzhno-Priobskiy GPP" Kopotilov Yury Viktorovich.
29. According to the law, an oil producing company has the right to 5% combustion of associated gas dissolved in oil. The torch burns for emergency discharge and gas combustion in case of emergency situations.
30. Plant control center. The plant is automated as much as possible; only a couple of dozen people are required to manage a huge production of 20 hectares. Control is carried out around the clock, 365 days a year.
31. There are a lot of young people, which pleases, but in addition to them there are also experienced employees.
32. After the plant we go to the head office of Gazpromneft-Khantos, located in Khanty-Mansiysk.
33. The same 3D model bush, which is being developed by specialists here, as well as in St. Petersburg, is shown on the monitor screen.
34. The representative of Mr. N shows how the well goes down, how in one moment it goes strictly horizontally. As you dig, the oil will go. Also, on these screens you can see the state of all drilling rigs, what kind of oil is pumping at what moment, where repairs are taking place and other useful things. Everything is connected to computers and a person may not be in a cold field near the drilling rig, but sit with tea in a trailer at any distance from the well and control the drilling and production process in real time.
35. The building was built several years ago, it usually looks like most modern office buildings.
36. Well yard of the XXI century.
Thanks to the company for the invitation to the drilling
Offshore oil production, along with the development of shale and hard-to-recover hydrocarbon reserves, will eventually displace the development of traditional onshore "black gold" deposits due to the depletion of the latter. At the same time, the receipt of raw materials in the offshore areas is carried out mainly using expensive and time-consuming methods, while the most complex technical complexes are involved - oil platforms
Specificity of offshore oil production
The dwindling reserves of traditional onshore oil fields have forced the leading companies in the industry to devote their energies to the development of rich offshore blocks. Pronedra wrote earlier that the impetus for the development of this production segment was given in the seventies, after the OPEC countries imposed an oil embargo.
According to the agreed estimates of experts, the estimated geological oil reserves located in the sedimentary layers of the seas and oceans reach 70% of the total world volumes and may amount to hundreds of billions of tons. Of this volume, about 60% falls on the shelf areas.
To date, half of the four hundred oil and gas bearing basins in the world covers not only continents on land, but also extends on the shelf. Now about 350 deposits are being developed in different zones of the World Ocean. All of them are located within the shelf areas, and the extraction is carried out, as a rule, at a depth of up to 200 meters.
At the current stage of technology development, oil production in offshore areas is associated with high costs and technical difficulties, as well as with a number of external unfavorable factors... Obstacles to effective work the sea is often characterized by a high seismicity index, icebergs, ice fields, tsunamis, hurricanes and tornadoes, permafrost, strong currents and great depths.
The rapid development of offshore oil production is also hindered by the high cost of equipment and field development works. Operating costs increase as the depth of production, rock hardness and thickness increase, as well as the distance of the field from the coast and the complication of the bottom topography between the extraction zone and the shore where the pipelines are laid. Serious costs are also associated with the implementation of measures to prevent oil leaks.
The cost of the drilling platform alone, designed to operate at depths of up to 45 meters, is $ 2 million. The equipment, which is designed for a depth of up to 320 meters, can already cost $ 30 million. On average, it costs at $ 113 million
Shipment of produced oil to a tanker
The operation of a mobile drilling platform at a depth of 15 meters is estimated at $ 16 thousand per day, 40 meters - $ 21 thousand, a self-propelled platform when used at a depth of 30-180 meters - $ 1.5-7 million. The cost of developing fields in the sea makes them profitable only in cases when it comes to large oil reserves.
It should be borne in mind that the cost of oil production in different regions will be different. The work associated with the discovery of a field in the Persian Gulf is estimated at $ 4 million, in the seas of Indonesia - $ 5 million, and in the North Sea prices rise to $ 11 million. for permission to develop an onshore section.
Types and arrangement of oil platforms
When extracting oil from the world's oceans, operating companies, as a rule, use special offshore platforms. The latter are engineering complexes with the help of which both drilling and direct extraction of hydrocarbon raw materials from the seabed are carried out. The first oil platform to be used offshore was launched in the US state of Louisiana in 1938. The world's first directly offshore platform called "Oil Rocks" was put into operation in 1949 in the Azerbaijani Caspian Sea.
The main types of platforms:
- stationary;
- loosely fixed;
- semi-submersible (exploration, drilling and production);
- self-elevating drilling rigs;
- with stretched supports;
- floating oil storage facilities.
Floating drilling rig with telescopic legs "Arctic"
Different types of platforms can be found in both pure and combined forms. The choice of this or that type of platform is associated with specific tasks and conditions of field development. We will consider the use of different types of platforms in the process of applying the main technologies of offshore production below.
Structurally, the oil platform consists of four elements - a hull, anchoring system, a deck and an oil rig. The hull is a triangular or quadrangular pontoon mounted on six columns. The structure is kept afloat due to the fact that the pontoon is filled with air. The deck houses drill pipes, cranes and a helipad. The rig directly lowers the drill to the seabed and raises it as needed.
1 - drilling rig; 2 - helipad; 3 - anchor system; 4 - body; 5 - deck
The complex is held in place by an anchor system that includes nine winches along the sides of the platform and steel cables. Each anchor weighs 13 tons. Modern platforms are stabilized at a given point not only with the help of anchors and piles, but also with advanced technologies, including positioning systems. The platform can be anchored in the same place for several years, regardless of the weather conditions at sea.
The drill, whose work is controlled by underwater robots, is assembled in sections. The length of one section, consisting of steel pipes, is 28 meters. Boers are produced with fairly wide capabilities. For example, the drill of the EVA-4000 platform can include up to three hundred sections, which makes it possible to deepen 9.5 kilometers.
Drilling oil platform
The construction of drilling platforms is carried out by delivering the base of the structure to the production area and flooding. Already on the received "foundation" and build on the rest of the components. The first oil platforms were created by welding from profiles and pipes of truncated pyramid-shaped lattice towers, which were firmly nailed to the seabed with piles. Drilling equipment was installed on such structures.
Construction of the Troll oil platform
The need to develop deposits in northern latitudes, where ice resistance of platforms is required, led to the fact that engineers came up with a project for the construction of caisson foundations, which in fact were artificial islands. The caisson is filled with ballast, usually sand. With its weight, the base is pressed against the bottom of the sea.
Stationary platform "Prirazlomnaya" with a caisson base
The gradual increase in the size of the platforms led to the need to revise their design, so the developers from Kerr-McGee (USA) created a project of a floating object with the shape of a navigation pole. The structure is a cylinder, in the lower part of which the ballast is placed. The bottom of the cylinder is attached to the bottom anchors. This decision made it possible to build relatively reliable platforms of truly cyclopean dimensions, designed for work at ultra-deep depths.
Floating semi-submersible drilling rig "Polar Star"
However, it should be noted that there is no big difference between the offshore and onshore rigs directly in the oil recovery and shipping procedures. For example, the main components of a fixed-type platform offshore are identical to those of an onshore oil rig.
Offshore drilling rigs are characterized primarily by their autonomy. To achieve this quality, the units are equipped with powerful electric generators and water desalination plants. Platform replenishment is carried out by service vessels. Besides, sea transport it is also used to move structures to work points, in rescue and fire-fighting activities. Naturally, the transportation of the obtained raw materials is carried out using pipelines, tankers or floating storage facilities.
Offshore technology
At the present stage of the industry development, inclined wells are drilled at small distances from the production site to the coast. At the same time, an advanced development is sometimes used - remote-type control of the processes of drilling a horizontal well, which ensures high control accuracy and allows you to give commands to drilling equipment at a distance of several kilometers.
The depths at the sea boundary of the shelf are usually of the order of two hundred meters, but sometimes they reach half a kilometer. Depending on the depth and distance from the coast, when drilling and extracting oil, they are used different technologies... In shallow areas, fortified foundations are being built, a kind of artificial islands. They serve as the basis for the installation of drilling equipment. In a number of cases, operating companies surround the work area with dams, after which water is pumped out of the resulting pit.
If the distance to the coast is hundreds of kilometers, then in this case a decision is made to build an oil platform. Stationary platforms, the simplest in design, can only be used at depths of several tens of meters; shallow water allows the structure to be fixed with concrete blocks or piles.
Stationary platform LSP-1
At depths of about 80 meters, floating platforms with supports are used. Companies in deeper areas (up to 200 meters), where securing the platform is problematic, use semi-submersible drilling rigs. Keeping such complexes in place is carried out using a positioning system consisting of underwater propulsion systems and anchors. If we are talking about ultra-great depths, then in this case, drilling ships are involved.
Drilling ship Maersk Valiant
Wells are equipped with both single and cluster methods. Recently, mobile drilling bases have begun to be used. Offshore drilling is carried out using risers - large-diameter pipes that go down to the bottom. After drilling is completed, a multi-ton BOP (blowout preventer) and wellhead equipment are installed at the bottom to avoid oil leakage from the new well. Equipment for monitoring the well condition is also being launched. After the start of production, oil is pumped to the surface via flexible pipelines.
Application different systems offshore production: 1 - inclined wells; 2 - stationary platforms; 3 - floating platforms with supports; 4 - semi-submersible platforms; 5 - drilling ships
The complexity and high-tech nature of the offshore development processes is obvious, even if you do not go into technical details. Is it advisable to develop this production segment, given the considerable attendant difficulties? The answer is unequivocal - yes. Despite the obstacles in the development of offshore blocks and high costs in comparison with work on land, oil produced in the waters of the World Ocean is still in demand in the context of a continuous excess of demand over supply.
Let us remind you that Russia and Asian countries are planning to actively increase the capacities involved in offshore production. This position can be safely considered practical - as the reserves of "black gold" on land are depleted, work at sea will become one of the main ways of obtaining oil raw materials. Even taking into account the technological problems, cost and labor intensity of offshore production, oil extracted in this way has not only become competitive, but has long and firmly occupied its niche in the industry market.
The magazine is charming vl_ad_le_na read a great post on oil production. Publishing with permission of the author.
What is oil?
Oil is a mixture of liquid hydrocarbons: paraffins, aromatics and others. In fact, oil is not always black - sometimes it is green (Devonian, I used to have it in a jar, sorry, I threw it away), brown (most common) and even white (transparent, it seems to be found in the Caucasus).
Oil is divided by quality into several classes depending on the chemical composition - accordingly, its price changes. In addition, associated gas is very often dissolved in oil, which burns so brightly in flares.
The gas can be dissolved from 1 to 400 cubic meters in a cubic meter of oil. That is, dofiga. This gas itself mainly consists of methane, but due to the difficulty of its preparation (it must be dried, purified and brought up to the Wobbe GOST numbers - so that there is a strictly defined heat of combustion), associated gas is very rarely used for domestic purposes. Roughly speaking, if gas from the field is put into an apartment in a gas stove, the consequences can be from soot on the ceiling to a damaged stove to death and poisoning (for example, hydrogen sulfide).
Oh yes. Another associated nasty thing in oil is dissolved hydrogen sulfide (because oil is organic matter). It is highly toxic and highly corrosive. This imposes its own difficulties on oil production. FOR OIL PRODUCTION. Professionalism, which, by the way, I do not use.
Where did the oil come from?
On this score, there are two theories (more -). One is inorganic. It was first expressed by Mendeleev and consists in the fact that water flowed past the incandescent carbides of metals, and, thus, hydrocarbons were formed. The second is organic theory. It is believed that oil “matured”, as a rule, in marine and lagoon conditions, by the decomposition of organic remains of animals and plants (silts) under certain thermobaric conditions (high pressure and temperature). Basically, research supports this theory.
What is geology for?
It is probably worth mentioning the structure of our Earth. In my opinion, everything is beautiful and clear in the picture.
So, oil geologists deal only with the earth's crust. It consists of a crystalline basement (where oil is sooooo rare, since these are igneous and metamorphic rocks) and a sedimentary cover. The sedimentary cover consists of sedimentary rocks, but I will not delve into geology. I can only say that the depth of oil wells is usually about 500 - 3500 m. It is at this depth that oil lies. Above is usually only water, below - a crystalline basement. The deeper the breed, the earlier it was deposited, which is logical.
Where does the oil come from?
Contrary to some common myths about "oil lakes" underground, oil is trapped. To simplify, the traps in a vertical section look like this (water is the eternal companion of oil):
(A fold curved with its "back" upward is called an anticline. And if it looks like a bowl, it is a syncline, the oil does not stay in the synclines).
Or like this:
And in plan, they can be round or oval rises. Sizes range from hundreds of meters to hundreds of kilometers. One or more of these traps located nearby is an oil field.
Since oil is lighter than water, it floats upward. But so that the oil does not leak anywhere else (to the right, left, up or down), the reservoir with it must be limited by the cap rock from above and below. These are usually clays, dense carbonates or salts.
Where do the bends inside the earth's crust come from? After all, rocks are deposited horizontally or almost horizontally? (if they are deposited in piles, then these piles are usually quickly smoothed out by wind and water). And the bends - ups and downs - arise as a result of tectonics. Have you seen the words "turbulent convection" in the picture with a cut of the Earth? This very convection moves the lithospheric plates, which leads to the formation of cracks in the plates, and, consequently, displacements of blocks between cracks and changes in the internal structure of the Earth.
How does the oil come from?
Oil does not occur by itself, as it was already said, oil lakes do not exist. Oil is in the rock, namely, in its voids - pores and cracks:
The rocks are characterized by properties such as porosity is the fraction of the volume of voids in the rock - and permeability- the ability of the rock to pass a liquid or gas through itself. For example, ordinary sand has a very high permeability. And concrete is much worse. But I dare to assure that the rock, which lies at a depth of 2000 m from high pressure and temperature properties are much closer to concrete than to sand. I felt. However, oil is extracted from there.
This is a core - a cut-out piece of rock. Dense sandstone. The depth is 1800 m. There is no oil in it.
Another important addition is that nature abhors a vacuum. Almost all porous and permeable rocks, as a rule, are water-saturated, i.e. there is water in their pores. Salty as it flowed through many minerals. And it is logical that some of these minerals are carried away together with water in a dissolved form, and then, when the temperature and pressure conditions change, fall out in these very pores. Thus, the grains of the rock become held together by salts and this process is called cementing. That is why, by and large, wells do not crumble immediately during drilling - because the rocks are cemented.
How is oil found?
Usually, first, according to seismic prospecting: they start vibrations on the surface (by an explosion, for example) and measure the time of their return to the receivers.
Further, according to the return time of the wave, the depth of one or another horizon is calculated at different points on the surface and maps are built. If an uplift is detected on the map (= anticlinal trap), it is checked for oil by drilling a well. Not all traps contain oil.
How are wells drilled?
A well is a vertical mine working with a length many times the width.
Two facts about wells: 1. They are deep. 2. They are narrow. The average diameter of a well at the entrance to the formation is about 0.2-0.3 m. That is, a person cannot get through there unambiguously. Average depth - as already mentioned, 500-3500 m.
Wells are being drilled from drilling rigs. There is such a tool for crushing rock as a chisel. Notice, not a drill. And it is completely different from that very helical device from "Teenage Mutant Ninja Turtles".
The bit is suspended on drill pipes and rotates - it is pressed to the bottom of the well by the weight of these very pipes. There are different principles for driving the bit, but usually the entire drill string is rotated to rotate the bit and crush the rock with its teeth. Also, drilling fluid is constantly pumped into the well (inside the drill pipe) and pumped out (between the wall of the well and the outer wall of the pipe) in order to cool this entire structure and carry away particles of crushed rock.
What is a tower for? To hang these same drill pipes on it (after all, in the process of drilling, the upper end of the string goes down, and new pipes must be screwed to it) and to lift the pipe string to replace the bit. Drilling one well takes about a month. Sometimes a special annular bit is used, which, when drilling, leaves the central column of the rock - the core. The core is selected for studying the properties of rocks, although it is expensive. There are also inclined and horizontal wells.
How do you know where which layer lies?
A person cannot go down into a well. But we need to know what we drilled there? When a well is drilled, geophysical probes are lowered into it on a wireline. These probes operate on completely different physical principles of operation - intrinsic polarization, induction, resistance measurement, gamma radiation, neutron emission, borehole diameter measurement, etc. All curves are written to files, so this is a nightmare:
Now geophysicists are getting into the work. Knowing the physical properties of each rock, they distinguish strata by lithology - sandstones, carbonates, clays - and perform a breakdown of the section by stratigraphy (i.e. what epoch and time the reservoir belongs to). I think everyone has heard about Jurassic Park:
In fact, there is a much more detailed subdivision of the section into tiers, horizons, units, etc. - but we don't care now. It is important that oil reservoirs (reservoirs capable of producing oil) are of two types: carbonate (limestone, like chalk, for example) and terrigenous (sand, only cemented). Carbonates are CaCO3. Terrigenous - SiO2. If it's rude. It is impossible to say which is better, they are all different.
How is the well prepared for operation?
After the well is drilled, it is cased. This means - a long string of steel casing pipes is lowered (with a diameter almost like a well), and then ordinary cement slurry is pumped into the space between the wall of the well and the outer wall of the pipe. This is done so that the well does not crumble (after all, not all rocks are well cemented). In the section, the well now looks like this:
But we closed the formation we needed with casing and cement! Therefore, the casing is perforated against the formation (how do you know where the required formation is? Geophysics!). A perforator with explosive charges embedded in it descends, again, on a cable. There the charges are triggered and holes and perforation channels are formed. Now we do not care about water from neighboring layers - we perforated the well just opposite the one we need.
How is oil produced?
The most interesting part, I think. Oil is much more viscous than water. I think viscosity is intuitive. Some petroleum bitumen, for example, are similar in viscosity to butter.
I'll come in from the other end. Fluids in the reservoir are under pressure - the overlying layers of rocks push against them. And when we drill a well, nothing presses from the side of the well. That is, in the area of the well, the pressure is low. A pressure drop, called a depression, is created, and it is this drop that causes oil to start flowing towards the well and appear in it.
There are two simple equations that all oil workers should know to describe oil flow.
Darcy's equation for straight flow:
Dupuis equation for plane-radial flow (just the case of fluid inflow to the well):
Actually, we stand on them. It is not worthwhile to go further into physics and write the equation of the unsteady inflow.
From a technical point of view, there are three most common methods of oil production.
Fountain. This is when the reservoir pressure is very high, and oil not only enters the well, but also rises to the very top and overflows (well, in fact, it does not overflow, but into the pipe and further).
Sucker rod pump (sucker rod pump) and ESP (electric centrifugal pump). The first case is a conventional rocker.
The second one is not visible at all on the surface:
Note that there are no towers. The tower is only needed for running / lifting pipes in the well, but not for production.
The essence of the pumps is simple: creating additional pressure so that the liquid entering the well can rise through the well to the surface of the earth.
It is worth remembering an ordinary glass of water. How do we drink from it? We tilt, right? But the well cannot be tilted. But in a glass of water, you can lower the tube and drink through it, drawing in the liquid through your mouth. This is approximately how the well works: its walls are the walls of the nozzle, and instead of a tube, a tubing string is lowered into the well. Oil rises through pipes.
In the case of sucker rod pumps, the rocking machine moves its "head" up and down, respectively, setting the bar in motion. The rod, when moving up, carries the pump with it (the lower valve opens), and when it moves down, the pump falls (opens the upper valve). So, little by little, the liquid rises up.
The ESP works directly from electricity (with a motor, of course). The wheels (horizontal) spin inside the pump, there are slots in them, so the oil rises to the top.
I must add that the open gushing of oil, which people like to show in cartoons, is not only emergency situation, but also an environmental disaster and millions in fines.
What to do when oil is poorly produced?
Over time, oil ceases to be squeezed out of the rock under the weight of the overlying strata. Then the reservoir pressure maintenance system comes into operation - maintaining the reservoir pressure. Injection wells are drilled and high pressure water is pumped into them. Naturally, the injected or produced water will sooner or later enter the production wells and will rise upward along with the oil.
It should also be noted that the greater the share of oil in the flow, the faster it flows, and vice versa. Therefore, the more water flows with the oil, the more difficult it is for the oil to get out of the pores and enter the well. The dependence of the fraction of oil permeability on the fraction of water in the flow is presented below and is called the curves of relative phase permeabilities. This is also a very useful concept for an oilman.
If the bottomhole formation zone is contaminated (by small particles of rock carried away with oil, or solid paraffins have fallen out), then acid treatments are carried out (the well is stopped and a small volume of hydrochloric acid is pumped into it) - this process is good for carbonate formations, because they dissolve. And for terrigenous (sandstones) acid do not care. Therefore, hydraulic fracturing is carried out in them - a gel is pumped into the well under very high pressure, so that the formation begins to crack in the area of the well, then proppant is pumped in (ceramic balls or coarse sand so that the crack does not close). After that, the well starts to work much better, because the obstructions to the flow have been removed.
What happens to the oil afterwards when it is produced?
First, oil rises to the surface of the earth in a pipe that runs from each well. 10-15 nearby wells are connected by these pipes to one metering device, where it is measured how much oil has been produced. Then the oil goes for preparation in accordance with GOST standards: salts, water, mechanical impurities (small particles of rock) are removed from it, if necessary, then hydrogen sulfide and how much gas?). Marketable oil goes to the refinery. But the plant may be far away, and then the Transneft company comes into play - main pipelines for finished oil (as opposed to field pipelines for crude oil with water). Oil is pumped through the pipeline with the same ESPs, only laid on one side. The impellers rotate in them in the same way.
The water separated from the oil is pumped back into the reservoir, the gas is flared or sent to a gas processing plant. And oil is either sold (abroad by pipelines or tankers), or goes to an oil refinery, where it is distilled by heating: light fractions (gasoline, kerosene, naphtha) go for fuel, heavy paraffinic ones - for raw materials for plastics, etc., and the heaviest fuel oil with a boiling point above 300 degrees are usually used as fuel for boiler houses.
How is all this regulated?
There are two main project documents for oil production: a project for calculating reserves (it substantiates that there is just so much oil in the reservoir, and not more and not less) and a development project (it describes the history of the field and proves that it is necessary to develop it in this way, and not otherwise).
To calculate reserves, geological models are built, and for a development project - hydrodynamic models (where it is calculated how the field will work in one mode or another).
How much does it all cost?
I must say right away that all prices are usually confidential. But I can roughly say: a well in Samara costs 30-100 million rubles. depending on the depth. A ton of marketable (not refined) oil costs differently. When I counted the first diploma, they gave a value of about 3000 rubles, when the second - about 6000 rubles, the time difference is a year, but these may not be real values. Now I do not know. Taxes account for at least 40% of profits, plus property tax (based on the book value of the property) plus mineral extraction tax. Add the money required for wages, electricity, well repairs, and field facilities — the construction of pipelines and equipment for gathering and treating oil. Very often, the economics of development projects goes into the negative, so you have to contrive to work in a positive way.
I will add such a phenomenon as discounting - a ton of oil produced next year is less valuable than a ton of oil produced this year. Therefore, we need to intensify oil production (which also costs money).
So, I briefly outlined what I studied for 6 years. The whole process, from the appearance of oil in the reservoir, exploration, drilling, production, refining and transportation, to sale - you can see that this requires specialists of completely different profiles. I hope that at least someone read this long post - and I have cleared my conscience and dispelled at least a few of the myths surrounding oil.
