Selection of oil recovery system and facilities oil fields depends on dozens of factors: on the depth and quality of productive layers: the amount of recoverable reserves, their structure on degree of knowledge (): reservoir characteristics; composition and properties of oil: gas factor and composition of associated gases: saturation pressure of oil with gas: properties and conditions of occurrence of formation waters; positions of water-oil contact.

In addition to the listed main development indicators, natural and climatic characteristics, engineering and geological conditions are taken into account during the development of the field.

One of the main requirements for development is rationalization: ensuring the specified production rates with minimal capital investments and minimal impact on the environment. the most important integral part field development design is the allocation of operational facilities. The part of the oil deposit allocated for operation by an independent network of production and injection wells is called a production facility.

Explored deposits are considered prepared for industrial development subject to the following conditions:

· obtained a license for the right to use subsoil;

· experimental-industrial operation of separate sections was carried out;

· balance reserves of hydrocarbons of industrial importance, make up at least 80% of the category, and up to 20% of the category;

Raw material base assessed building materials and sources of water supply;

· approved documents for the utilization of APG, gas condensate and other associated valuable components;

· Measures are taken to prevent pollution of the environment and ensure the safe conduct of work.

Master plan requirements

The scheme of the general plan of the field provides for the placement of the mouths of oil, gas, injection single wells and clusters, GZU, BPS. installations of preliminary discharge of formation waters (UPS), cluster pumping stations(CPS), CS, engineering communications (roads, oil and gas pipelines, water conduits, power lines, communication lines, cathodic protection, etc.) that ensure the collection and transportation of well products, as well as the supply of electricity, heat, water and air.

The placement of industrial and auxiliary buildings and structures must be carried out according to their functional and technological purpose, taking into account explosive and fire hazards. When placing oil production facilities in the coastal areas of reservoirs, the planning marks of the sites are taken 0.5 m above the highest water horizon with a probability of exceeding it once every 25 years (wellheads, GZU) and once every 50 years (CS, CPS, BPS, UPS ).

Environmental measures and EIA elements are present in normative documents for the development of deposits. However, with the established practice of interaction between participants in the development of deposits, typical environmental problems are not solved in a preventive manner, but as they arise. There is a pattern - than in more remote location the deposit is located, the less stringent environmental restrictions are imposed on it and the greater environmental damage is caused to the environment.

In order to avoid social and environmental problems at the later stages of oil production, consultations with all interested organizations and individuals should be carried out already during the design of field development. The operation of oil fields harms the environment, regardless of the design features of structures and volumes of hydrocarbons produced. Carrying out costly environmental measures should be carried out in a timely manner (liquidation of wells, storage pits, land reclamation), and not be postponed indefinitely.

Technological safety of the operation of facilities in the chain "extraction - collection - preparation - transportation" is largely ensured by the uniformity of the development of oil reserves. To do this, it is necessary to have reliable information about the distribution of the energy potential of the reservoir, which is reflected using isobar maps. Here, the choice of well clustering scheme is fundamentally important. It is known that the larger the well pads, the more expensive the drilling of the well, since large bottomhole waste from the vertical is required (up to 2-4 km or more). However, this reduces the cost of communication corridors and increases the degree of environmental safety of the fishery as a whole.

well cluster

Under well pads, a site of a natural or artificial area of ​​​​the territory is allocated with wellheads located on it, technological equipment, engineering communications and office space. An enlarged cluster may include several dozen directional wells. The total oil flow rate of one well pad is taken up to 4000, and the gas factor - up to 200.

Well cluster technological structures usually include:

· wellhead sites of production and injection wells;

measuring installations;

· supply units for reagents-demulsifiers and inhibitors;

· blocks of gas-distributing and water-distributing;

blocks for pumping water into injection wells;

· ESP and SRP pump control stations;

foundations for pumping units;

· transformer substations;

sites for the repair unit;

· reservoir-collector and technological pipelines.

The well pad facilities may include a wastewater treatment unit (SWSU) with local injection of water into the reservoir. In this case, there is no energy-intensive pumping of formation waters to oil separation points and back, and there are no aggressive formation fluids in the transport corridors, which increases the environmental safety of the field.

The construction of wells with large bottomhole waste limits the use of deep rod pumps due to complications associated with abrasion of pipes. In order to avoid accidents, when choosing pumping equipment, preference is given to ESP and hydraulically driven pumping systems in a closed oil and gas gathering system. Such systems allow the supply of inhibitors to prevent corrosion and wax formation.

The system of facilities for oil treatment, discharge and injection of water is built depending on the distribution of reserves over the area of ​​the deposit, production rates, degree of water cut and gas saturation of oil, pressure at the wellhead, location of well clusters (Fig. 5.1). These facilities must provide:

· pressurized collection and transportation of well products to the CPS;

· separation of gas from oil and compressor-free transportation of gas of the first stage of separation to collection points, gas processing plant and for own needs;

· measurement of production costs of individual wells and clusters, accounting for the total production of products from all wells;

· preliminary dehydration of oil.

Rice. 5.1. Schematic diagram of the system for collecting well products in the oil field

Annotation: The choice of oil recovery system and oil field development depends on dozens of factors.

Scheme of arrangement of oil fields

The choice of an oil recovery system and the development of oil fields depends on dozens of factors: on the depth and quality of productive formations: the amount of recoverable reserves, their structure according to the degree of exploration (): reservoir characteristics; composition and properties of oil: gas factor and composition of associated gases: saturation pressure of oil with gas: properties and conditions of occurrence of formation waters; positions of water-oil contact.

In addition to the listed main development indicators, natural and climatic characteristics, engineering and geological conditions are taken into account during the development of the field.

One of the main requirements for development is rationalization: ensuring the specified production rates with minimal capital investments and minimal impact on the environment. The most important component of field development design is the allocation of production facilities. The part of the oil deposit allocated for operation by an independent network of production and injection wells is called a production facility.

Explored deposits are considered prepared for industrial development subject to the following conditions:

Master plan requirements

The scheme of the general plan of the field provides for the placement of the mouths of oil, gas, injection single wells and clusters, GZU, BPS. installations for preliminary formation water discharge (UPS), cluster pumping stations (CPS), compressor stations, engineering communications (roads, oil and gas pipelines, water conduits, power lines, communication lines, cathodic protection, etc.), providing processes for collecting and transporting well products, as well as the supply of electricity, heat, water and air.

The placement of industrial and auxiliary buildings and structures must be carried out according to their functional and technological purpose, taking into account explosive and fire hazards. When placing oil production facilities in the coastal areas of reservoirs, the planning marks of the sites are taken 0.5 m above the highest water horizon with a probability of exceeding it once every 25 years (wellheads, GZU) and once every 50 years (CS, CPS, BPS, UPS ).

Environmental measures and elements of EIA are included in the regulatory documents for the development of deposits. However, with the established practice of interaction between participants in the development of deposits, typical environmental problems are not solved in a preventive manner, but as they arise. There is a pattern - the more remote the deposit is located, the less severe environmental restrictions are imposed on it and the greater the environmental damage caused to the environment.

In order to avoid social and environmental problems at the later stages of oil production, consultations with all interested organizations and individuals should be carried out already during the design of field development. The operation of oil fields harms the environment, regardless of the design features of structures and volumes of hydrocarbons produced. Carrying out costly environmental measures should be carried out in a timely manner (liquidation of wells, storage pits, land reclamation), and not be postponed indefinitely.

Technological safety of the operation of facilities in the chain "extraction - collection - preparation - transportation" is largely ensured by the uniformity of the development of oil reserves. To do this, it is necessary to have reliable information about the distribution of the energy potential of the reservoir, which is reflected using isobar maps. Here, the choice of well clustering scheme is fundamentally important. It is known that the larger the well pads, the more expensive the drilling of the well, since large bottomhole waste from the vertical is required (up to 2-4 km or more). However, this reduces the cost of communication corridors and increases the degree of environmental safety of the fishery as a whole.

well cluster

A site of a natural or artificial area of ​​the territory with wellheads, technological equipment, engineering communications and office premises located on it is allocated for well clusters. An enlarged cluster may include several dozen directional wells. The total oil flow rate of one well pad is taken up to 4000, and the gas factor - up to 200.

Well cluster technological structures usually include:

• wellhead sites of production and injection wells;
• measuring installations;
• supply units for reagents-demulsifiers and inhibitors;
• gas distribution and water distribution blocks;
• units for pumping water into injection wells;
• ESP and SRP pump control stations;
• foundations for pumping units;
• transformer substations;
• sites for the repair unit;
• collection tank and technological pipelines.

The well pad facilities may include a wastewater treatment unit (SWSU) with local injection of water into the reservoir. In this case, there is no energy-intensive pumping of formation waters to oil separation points and back, and there are no aggressive formation fluids in the transport corridors, which increases the environmental safety of the field.

The construction of wells with large bottom hole waste limits the use of downhole rod pumps due to the complications associated with pipe abrasion. In order to avoid accidents, when choosing pumping equipment, preference is given to ESP and hydraulically driven pumping systems in a closed oil and gas gathering system. Such systems allow the supply of inhibitors to prevent corrosion and wax formation.

The system of facilities for oil treatment, discharge and injection of water is built depending on the distribution of reserves over the area of ​​the deposit, production rates, degree of water cut and gas saturation of oil, pressure at the wellhead, location of well clusters (Fig. 5.1). These facilities must provide:

• pressurized collection and transportation of well products to the CPS;
• separation of gas from oil and non-compressor transportation of gas of the first stage of separation to collection points, gas processing plant and for own needs;
• measurement of production costs of individual wells and clusters, accounting for the total production of products from all wells;
• preliminary dehydration of oil.

Rice. 5.1.

Group metering stations

The gas-liquid mixture from the production wells enters the GZU, in which the periodic measurement in the measuring separator of the liquid and gas flow rates of each well is automatically performed. The number of installations is determined by calculations. Blocks for injection of a demulsifying agent and a corrosion inhibitor are located on the sites of the GZU.

Booster pumping station

In cases where the distance from the well pads to the CPS is large, and the wellhead pressure is not enough to pump fluids, a BPS is constructed. The mixture enters the BPS through oil-gathering pipelines after the GZU.

The DNS includes the following block structures:

• the first separation stage with preliminary gas extraction;
• preliminary dehydration and purification of formation water;
• measuring oil, gas and water;
• pumping and compressor air unit;
• reagent injection before the first separation stage;
• injection of inhibitors into gas and oil pipelines;
• emergency containers.

The construction of a booster pumping station is necessary because pumping equipment does not allow pumping mixtures with a high gas content due to the occurrence of cavitation processes. The gas separated as a result of pressure reduction in the first separation stage is most often fed to a flare or for local use. Oil and water with the dissolved remaining gas enter the second stage separators at the CPS and OTU.

Central collection point

At the CPS, crude oil goes through a full processing cycle, which includes two- or three-stage degassing of oil using separators and bringing the oil to the required conditions in terms of saturated vapor pressure. After separation, the gas is cleaned from dropping liquids and fed for recycling or processing. The gas of the first and second separation stages is transported under its own pressure. The end stage gas needs to be compressed for further use.

Here, at the CPS, oil is dehydrated and desalted to marketable standards. Produced waters are separated from crude oil at the oil treatment unit (OTU) as part of the CPS. In a special tank, oil is settled, the oil emulsion is heated in tube furnaces and desalted. After that, the commercial oil enters the reservoir with subsequent pumping to the MN.

tank farms

The presence of a reserve fleet of tanks is a mandatory attribute of all technological schemes collection, preparation and transportation of oil and gas. Standard RVS type tanks are used to create reserves:

• raw materials supplied to the OTU, required in the amount of the daily volume of well production;
• commercial oil in the volume of the daily productivity of the OTU.

In addition, reservoirs various volumes necessary for the reception of reservoir and waste water, as well as for emergency discharges.

To discharge paraffin deposits from cleaning (steaming) of tanks, earthen storage pits are arranged. In addition, reservoirs are a source of atmospheric pollution due to the evaporation of hydrocarbons stored in them.

Compressor stations

CSs can be independent field development facilities or be part of the complex of technological facilities of the CPF. CS are designed to supply oil gas to the GPP, to compress gas in the gas lift production system and prepare it for transportation.

To remove gas from the cavity of the reciprocating compressor, a gas discharge candle is provided at the inlet gas pipeline of each compressor compression stage with stop valves installed on it. The height of the candle is at least 5 m and is determined by gas dispersion calculations.

Flare system

Oil gas that cannot be accepted for transportation, as well as gas from purging equipment and pipelines, is sent to the emergency flaring system of the BPS.

The diameter and height of the torch are determined by calculation, taking into account the permissible concentration of harmful substances in the surface air layer, as well as the permissible thermal effects on humans and objects. The height of the pipe must be at least 10 m, and for gases containing hydrogen sulfide, not less than 30 m. The gas velocity at the mouth of the flare stack is taken taking into account the exclusion of flame separation, but not more than 80 m/s.

The flare system of the CPF is provided for the discharge of gases and vapors:

• permanent - from installations for regeneration of sorbents and stabilization of hydrocarbon condensates;
• periodic - before the release of the apparatus before steaming, purging and repair;
• emergency - when discharged from safety valves and other emergency discharges.

The torch is equipped with automatic remote ignition and independent supply of fuel gas to the ignition device. A condensate collector is placed in front of the flare stack to catch condensate.

oil pipelines for transporting marketable oil from the CPS to the main PS of the main pipeline:

gas pipelines for supplying petroleum gas from separation units to GTU, CS, CPS, GPP and own needs:

gas pipelines for gas supply from the CPS to the main compressor station of the main pipeline.

The natural accumulation of oil in the subsoil is called an oil deposit. Almost every oil deposit also contains gas, i.e. is essentially an oil and gas deposit. In nature, there are also purely gas deposits, i.e. accumulations in porous rocks of natural gas.

The main known oil and gas fields are concentrated in sedimentary rocks. characteristic feature sedimentary rocks - their layering. These rocks are composed mainly of almost parallel layers (layers), differing from each other in composition, structure, hardness and color. The bottom bounding surface is called sole, and above - roofing.

Layers of sedimentary rocks can occur not only horizontally, but also in the form folds(Fig. 1), formed during oscillatory, tectonic and mountain building processes. The bending of the formation, directed by the convexity upwards, is called anticline and bulge down - syncline. Neighboring anticline and syncline together form full fold.

Fig.1. Fold formed by sedimentary rocks.

Fig.2. Schemes of structural traps.

a - a trap in the crest of a local uplift; b - tectonically

shielded trap in the crest part of the local uplift.

In Russia, almost 90% of the found oil and gas are located in anticlines, while abroad - about 70%. Anticlines are on average 5...10 km long, 2...3 km wide, 50...70 m high. However, giant anticlines are also known. Thus, the largest oil field in the world, Gavar (Saudi Arabia), has dimensions in terms of 225x25 km and a height of 370 m, and the Urengoy gas field (Russia): 120x30 km with a height of 200 m.

By permeability rocks are divided into permeable (collectors) and impermeable (tires). collectors- these are any rocks that can contain and release liquids and gases, as well as pass them through themselves with a pressure drop. Pore ​​reservoirs have the best reservoir properties.

Other types of collectors may also have good abilities to contain and release liquids and gases, as well as pass them through themselves. For example, in some fields in Saudi Arabia, interconnected systems of fractures create channels up to 30 km long. More than 50% of discovered oil reserves are confined to fractured reservoirs abroad, and 12% in Russia.

Tires These are practically impenetrable rocks. Usually they are rocks of chemical or mixed origin, not disturbed by cracks. Most often, clays play the role of tires: when wetted with water, they swell and close all the pores and cracks in the rock. In addition, rock salt and limestone can be used as tires.

Industrial deposits of oil and gas are found only in sedimentary rocks. Oil and gas fill the pores and voids between the individual particles of these rocks.

It is known that sedimentary rocks include sands, sandstones, limestones, dolomites, clays, etc. However, industrial accumulations of oil are not found in clayey rocks. Clay layers in oil fields play only the role of impermeable overlaps, between which lie more porous rocks saturated with oil, gas or water. If there were no clayey rocks underlying and covering accumulations of oil or gas, then the latter would be dispersed throughout the entire thickness of the earth's crust.

For the formation of oil and gas deposits, in addition to the presence of porous rocks, closed from above by impermeable layers, one more condition is required: certain structural forms of the reservoir. Long-term practice of exploitation of oil and gas deposits has shown that oil and gas do not occur in undisturbed (horizontal) layers, all their accumulations are in various folds.

The most common and most important in the structure of oil and gas deposits are structural forms of the anticlinal type and structural forms associated with the monoclinal occurrence of reservoirs. Most of the world's oil and gas deposits are confined to these structural forms.

On fig. 1 shows a diagram of a reservoir-type oil and gas deposit. Its main elements and parameters are the geometric dimensions and shape, as well as the position of the external and internal contours of oil and gas.

Fig.3. Scheme of an oil and gas deposit of reservoir type

1 – internal contour of gas content; 2 – outer contour of gas content;

3 – inner contour of oil-bearing capacity; 4 – outer contour of oil-bearing capacity.

The line of intersection of the surface of the oil-water contact with the top of the reservoir is called the outer contour of the oil-bearing capacity, and with the bottom of the reservoir - the inner contour of the oil-bearing capacity.

The accumulation of free gas above oil in a reservoir is called a gas cap.

The line of intersection of the surface of the oil and gas interface with the top of the reservoir represents the outer contour of the gas content, and with the base of the reservoir - the inner contour of the gas content.

In addition to reservoir-type oil and gas deposits, there are also massive oil or gas deposits confined to large massifs or reefs, usually composed of limestone. There are also reservoir shielded and lithologically limited deposits of oil and gas.

The constant companions of oil in oil deposits are oil gas and formation water. Their distribution along the height of the deposit, as can be seen from the diagram in Fig. 1 corresponds to their densities: gas is located in the upper parts of the anticline or monoclinal fold, oil lies below the gas, and the latter is propped up by water from below.

The volume of voids in the rock, consisting of pores, pore channels between individual grains and rock particles, cracks, caverns, etc., is commonly called porosity. The numerical value of porosity is determined by the ratio of the total volume of all voids in the rock to the entire volume of rock with voids.

The value of porosity of various rocks varies over a very wide range - from fractions of a percent to several tens of percent. So, for igneous rocks, porosity ranges from 0.05 to 1.25% of the total rock volume with voids, for oil sands - from 18 to 35%, for sandstones - from 13 to 28%. The permeability of the rock depends on the size of the pores and the channels connecting these pores. The larger the pore size, the higher the permeability and vice versa. For example, clays may have the same porosity as sands, ie. a unit volume of clayey rock can contain as much liquid as the same volume of sand. However, due to the negligibly small size of individual pores and channels between clay particles, the forces of cohesion and internal friction in them are so great that the movement of liquid or gas in the clay reservoir is almost absent. Clays are practically impermeable to liquid and gas.

In addition to the geometric volume of an oil or gas deposit, the porosity and permeability of the rocks that make up this deposit, its commercial value also depends on the amount of reservoir energy, on the quality of the oil contained in it, and, most importantly, on oil and gas saturation.

Oil saturation (gas saturation) is the ratio of the pore volume in the reservoir filled with oil (gas) to the total pore volume. The fact is that the pores of oil- or gas-containing rocks always contain water, which remains immobile in the process of exploitation of the deposit. This water is “bound” to the rock due to the action of the forces of adhesion of the rock to the water. It has been established that from the total volume of pores of oil-bearing rock, from 60 to 90% of the pores are filled with oil, the rest: the pore volume is filled with water.

The totality of oil and gas deposits located on one area of ​​the earth's surface is an oil or gas field.

Figure 4 schematically depicts a multilayer oil and gas field of an anticline type. In this field, reservoir A - purely gas, layers B and C - oil. The upper part of reservoir B is filled with gas, and the oil is propped up by formation water from below.

Fig.4. Scheme of an oil and gas field.

Oil is a complex multicomponent natural mixture consisting of paraffinic, naphthenic, aromatic hydrocarbons, heteroatomic compounds, resins, asphaltenes and other components. In addition, reservoir oil contains various gases, reservoir water, inorganic salts, and mechanical impurities.

1. Oil deposits and fields

1.1. Forms of occurrence of oil deposits

Oil saturates the pores, cracks and voids in rocks in the bowels of the Earth. The natural accumulation of oil in the subsoil is called an oil deposit. .

Oil deposits, as a rule, contain gaseous compounds, which can be both in a free state and in a dissolved state in oil. Therefore, the oil reservoir is essentially oil and gas. Gaseous compounds form the basis of associated petroleum gas.

There are also pure gas and gas condensate deposits in the subsoil. In gas condensate deposits, in addition to gas, the pores of the formation contain a certain volume of liquid compounds - condensate.

The totality of oil or gas deposits located on one area of ​​the earth's surface is an oil or gas field.

Industrial deposits of oil and gas are usually found in sedimentary rocks having a large number of large pores. Sedimentary rocks were formed as a result of the deposition of organic and inorganic substances at the bottom of water basins and the surface of continents.

A characteristic feature of sedimentary rocks is their layering. They are composed mainly of almost parallel layers ( layers), differing from each other in composition, structure, hardness and color. A field can have from one to several dozen oil or gas reservoirs.

If there is only one deposit in one area, then the deposit and the deposit are equivalent and such a deposit is called a single-layer deposit. In other cases, the deposits are multilayer.

The bottom bounding surface is called sole, above - roofing. Layers of sedimentary rocks can occur not only horizontally, but also in the form of folds due to mining processes. The bending of the formation, directed by the convexity upwards, is called anticline, way down - syncline. The adjacent anticline and syncline form a complete fold. The dimensions of the anticline are on average: length 5...10 km, width 2...3 km, height 50...70 m. Arabia (length 225 km, width 25 km, height 370 m). In Russia, almost 90% of explored oil and gas deposits are located in anticlines.

By permeability, rocks are divided into permeable ( collectors) and impenetrable ( tires). Reservoirs are rocks that can contain, pass and release liquids and gases.

Rice. 1.1. Scheme of a complete formation fold

There are the following types of collectors: porous(sands, sandstones), cavernous(having cavities - caverns formed due to the dissolution of salts with water), fissured(having micro- and macro-cracks in impermeable rocks, such as limestones) and mixed. Tires are practically impermeable rocks (usually clays).

For the formation of large accumulations of oil and gas, a number of conditions must be met: the presence of reservoirs, tires, as well as a reservoir of a special shape, once in which oil and gas appear to be in a dead end ( trapped). The accumulation of oil and gas occurs due to their migration in reservoirs from the area of ​​high to the area of ​​low pressure along the tires. There are the following main types of traps: anticlinal, tectonically screened, stratigraphically screened and lithologically screened. A tectonically screened trap is formed as a result of tectonic movements and vertical displacements of the earth's crust. A stratigraphically shielded trap is formed due to the overlapping of reservoirs with younger impermeable deposits. A lithologically shielded trap is formed when lenses of permeable rocks are surrounded by impermeable rocks. Once trapped, oil, gas, and water stratify.

Oil deposits are most often found in anticlinal traps, a diagram of which is shown in Fig. 1.2. The geometric dimensions of the deposit are determined by its projection on the horizontal plane.

Rice. 1.2. Scheme of an anticline type oil deposit:

1 – internal contour of gas content; 2 – outer contour of gas content;

3 – inner contour of oil-bearing capacity; 4 - outer contour of oil-bearing

The interface between gas and oil - gas-oil contact. The interface between oil and water - oil-water contact. The line of intersection of the surface of the gas-oil contact with the base of the formation is internal gas-bearing contour, with a roof - outer gas contour. The line of intersection of the surface of the oil-water contact with the base of the reservoir - inner contour of oil-bearing capacity, with a roof - outer contour of oil-bearing.

The shortest distance between the top and bottom of the formation is thickness formation. The distance along its major axis between extreme points the outer contour of oil-bearing capacity - length deposits. The distance along the minor axis between the extreme points of the outer contour of oil-bearing capacity - width deposits. The vertical distance from the base of the deposit to its highest point is power deposits.

The usual companion of oil in oil deposits are formation waters, which are usually found in the lower parts of the reservoir.

Formation waters located in the lower part of productive formations are called plantar, the volume of which is usually tens and hundreds of times larger than the oil part. Formation waters that extend over large areas outside the reservoir are called regional.

In the oil and gas part of the formations, water is retained in the form of thin layers on the walls of pores and cracks due to adsorption forces. This water during the exploitation of the deposit remains motionless and is called residual or related. Its content is about 10 to 30% of the total pore volume in oil fields and up to 70% in gas fields.

If there is free gas in the reservoir, then it will be in the upper part of the reservoir in the form gas hats.

The interface between gas, oil and water in oil reservoirs, or between gas and water in pure gas reservoirs, is a complex transition region. Due to the rise of water due to capillary forces in the pores of the rocks, there is no clear separation of water and oil, and the vertical water content varies from 100% to 30% or more in the elevated parts of the deposit. The height of this zone is from 3 to 5 meters or more.