3. transmission - major technical solutions applied during bovanenkovo

7/24/2019 3. Transmission - Major Technical Solutions Applied During Bovanenkovo

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MAJOR TECHNICAL SOLUTIONS APPLIED DURING BOVANENKOVO UKHTA GASTRUNKLINE SYSTEM ENGINEERING AND CONSTRUCTION

Oleg E. Aksyutin, Sergey V. Alimov, Anatolyi V. Chepkasov, Andrey V. Khoroshikh

OAO Gazprom

The Yamal Peninsula is one of Russias most strategically significant oil and gas provinces. 11 gas and15 oil, gas and condensate fields with approximately 16 trillion cubic meters

of explored and provisionally

evaluated gas reserves (ABC1+C2) and nearly 22 trillion cubic meters of in-place and probable gas reserves(C3+D3) have been discovered on the Yamal Peninsula and in the adjacent offshore areas. Condensatereserves (ABC1) are estimated at 230.7 million tons and oil reserves at 291.8 million tons.

The Cenomanian-Aptian deposits of the Bovanenkovskoye field are a paramount development target on theYamal. It is anticipated to increase the projected gas production at the Bovanenkovskoye field from thecurrent 115 billion cubic meters to 140 billion cubic meters per annum in the long run. In order to deliver theextracted gas to the Unified Gas Supply System, it is necessary to build the Bovanenkovo Ukhta gastrunkline system.

The gas pipeline with some 120 billion cubic meters at the annual throughput capacity comprises two 1,100-kilometer-long lines made of 1,420-millimeter pipes and includes a four-line 71-kilometer-long submergedcrossing via the Baidarata Bay made of 1,200-millimeter pipes. There will be 9 compressor stations (CS),operated at 11.8 MPa each and consisting of 2 compressor station buildings, at the gas pipeline. A total ofsome 90 gas pumping units (GPU) with the aggregate capacity exceeding 2,000 megawatts will be installedat the CSs.

Lets consider the major technical solutions relevant to the gas pipeline laying and compressor stationsconstruction in a harsh natural and climatic environment of the Yamal Peninsula.

Linear part

The gas pipeline route is featured by a harsh engineering, environmental and geological conditions. Thepipeline may be divided into 4 zones characterized with specific features.

Bovanenkovo Baidaratskaya CS zone (KP 0 KP 28 / KP 0 KP 123.3):

continuous permafrost is widespread;

thawed soils underlie waterway beds only;

annual average temperature of permafrost soils varies from minus 6.5 to minus 2.5C;

seasonal thawing depth, depending on the soil type, ranges between 0.3 and 1.0 meters;

high ice content in formations and presence of massive cavern-load ices;

permafrost soils cover over 90 per cent of the pipeline route.

Yarynskaya CS Gagaratskaya CS zone:

continuous permafrost is widespread;

thawed soils underlie waterway beds only;

annual average temperature of permafrost soils varies from minus 6.5 to minus 2.5C;

seasonal thawing depth ranges between 0.3 and 1.2 meters;

permafrost soils make up around 59 per cent of the pipeline route, while rocky and thawed soils cover38 and 3 per cent accordingly.

Gagaratskaya CS Vorkutinskaya CS zone (KP 317.6 KP 434.3):

continuous permafrost and insular permafrost areas are widespread;

annual average temperature of soil varies from minus 1 to minus 4C in continuous permafrost areas

and from 0 to minus 1.5C in insular permafrost areas; permafrost and thawed soils make up 62 and 38 per cent of the pipeline route, respectively;


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when thawing, permafrost loams lose their bearing capacity and turn into flow soils. The bulk of thawedsoils fall into the category of heaving soils.

Vorkutinskaya CS Ukhta zone (KP434.3 KP1,109.6):

permafrost soils have a discrete and insular nature (beneath the area influenced by pipelines);

varying along the gas pipeline route, permafrost soils make up 50-80 per cent in the beginning of thezone and 5-10 per cent in the middle of it;

the KP 780 Ukhta section is dominated by thawed soils;

the following exogenic processes hinder the pipeline construction:

swamping;

erosion and landsliding;

karstification.

The following major techniques were developed to lay the gas pipeline with a minimized cryogenic impact onthe gas transmission facilities:

Gas transmission at subzero temperatures in case the gas pipeline is buried underground in the areaof primarily continuous permafrost. For this purpose natural gas at the Bovanenkovskoye field iscooled to minus 2C before transmission. Downstream of the submerged crossing via the BaidarataBay, gas is cooled again to minus 2C at the gas cooling station of the Yarynskaya CS.

Mitigation of heaving and thermokarsting through reduction of the seasonal thawing depth. A full orpartial heat insulation of the pipe and the trench is performed for this purpose.

Stabilization of the pipeline in the designed position to protect it from landsliding. This is achievedthrough increasing the depth of certain pipeline sections. The soils near the bases and foundationfootings are fixed by non-energy intensive seasonal temperature stabilization means.

Lets get a deeper insight into the key ways of pipelaying at separate sections of the gas pipeline route.

The gas pipeline will be constructed with the use of 1,420-millimeter pipes made of X80 grade steel. Thepipes will have a triple-layer polyethylene exterior coating provided by the manufacturer and inner smooth

lining. The gas pipeline will be buried underground throughout its length. The pipeline burial depth isprojected to be no less than:

1.0 meter to the upper pipe in dry mineral soils;

1.0 meter to the ballast top in permafrost areas, water-saturated mineral soils and swamped areas.

In general, pipelines reflect the terrain relief. Vertical and horizontal curving is achieved through the use ofcold-bending laterals and elastic-bending pipes. The overall stability of gas pipelines is secured throughobserving the calculated elastic bending radiuses and through ballasting. In case of hillsides with thetransverse gradient of above 80 degrees, pipelaying is carried out through side cuts.

The Bovanenkovo Ukhta gas pipeline is characterized with various gas transmission temperatures atdifferent sections.

Taking into account temperature and soil conditions along the pipeline route, it is projected to apply thefollowing design solutions:

At the pipeline sections in permafrost areas with the gas transmission temperature ranging from minus2 to minus 7C the gas pipeline is laid without any heat insulation. In order to prevent floating-up withinthe period between construction completion and commissioning, the pipeline is ballasted with PKBU-MK-1420 polymer container ballasting devices, as a rule, at the sections prone to water-logging orswamping during seasonal thawing of the active layer, and with UBO-1420 concrete weighting loads atthe waterways prone to freezing to the bottom.

At the pipeline sections in permafrost areas with the gas transmission temperature of minus 7C theupper side of the pipeline is insulated. This type of insulation will be applied at the sections where theseasonal thawing depth is decreased due to the cold gas impact. This will hamper the natural runoff ofsubsurface waters from the active layer provoking intensive swamping and water-logging of the area

adjacent to the pipeline. The heat insulation materials are manufactured on the basis of the extrudedpolystyrene foam.


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As in the case mentioned above, gas pipeline ballasting is provided for at the sections prone to water-logging. The ballasting devices will be installed above the insulation.

Heat-insulated pipes will be laid in the areas of thawed soil. At the coastal sections the UBO-1420 typeweighting loads will be used for stabilizing the gas pipeline in the desired position. In the areas ofwaterway beds circular cast-iron weighting loads will be applied. The ballast will be installed above theinsulation.

At sections with longitudinal slopes, such as river valley slopes, soil-detention barriers made of KP-1.8type soil-saving containers are used in order to prevent soil removal from trenches.

In order to prevent erosion, river banks are reinforced with geogrids.

The gas pipeline insulation is protected from mechanical damage in permafrost and rocky soils with apad and a cushioning layer composed of soft soil brought to the site.

In addition, a provision is made for year-round cooling of natural gas down to subzero temperatures at thesections located between Bovanenkovo and the Baidaratskaya CS, as well as between the Yarynskaya CSand the Gagaratskaya CS. Gas cooling at these sections is required due to the fact that the gas pipeline runsthrough continuous permafrost areas.

At the rest of the sections gas cooling down to subzero temperatures at the compressor station outlet is notrequired.

Thus, it is possible to divide the gas pipeline route into sections by heat insulation type:

the Bovanenkovskoye field Baidaratskaya CS section: the gas pipeline is laid without heat insulation.Circumferential heat insulation is only applied when crossing streams, rivers and waterways;

the Baidaratskaya CS Yarynskaya CS section: circumferential heat insulation is used along theentire section;

the Yarynskaya CS Gagaratskaya CS section: heat insulation solutions are identical to those appliedfor the Bovanenkovskoye field Baidaratskaya CS section;

as for the remaining part of the pipeline, separate sections are heat-insulated where it is required dueto the natural gas temperature / adjacent soil temperature ratio.

Most of water crossings will be of the trench type providing for the gas pipeline burial under the waterwaybeds at the depth of at least 0.5 meters below the forecast level of waterbed erosion from the ballastedpipeline top, but no less than 1 meter away from the natural waterway bed level. The gas pipeline stability issecured through ballasting.

At cooled gas transmission sections water crossings will be made of heat-insulated pipes.

In case underground river crossing is not reasonable (steep banks, narrow riverbed), the above-groundbeam pipeline crossings are built equipped with dampeners.

Crossing via Baidarata Bay

The Baidarata Bay is characterized with unique environmental conditions: with an insignificant depth itfreezes to the bottom in winter. In addition, there are frequent spells of stormy weather and complex seabedsediments in the Bay. This impedes working activities except for several months a year. Pipelaying in these

severe climatic conditions and with such unique technical parameters is unprecedented not only in Russia,but also worldwide.

A four-line submerged Baidarata Bay crossing is projected to be made of 1,200-millimeter pipes sustaining11.8 MPa operating pressure. The crossing will be 70.6 kilometers long.

Depending on construction methods, the gas pipeline crossing via the Baidarata Bay is divided into thefollowing sections:

the Yamal onshore section (landmark post 0 LP 18);

the Yamal coastline crossing section (LP 18 LP 35);

the offshore section (LP 35 LP 679);

the Urals coastline crossing section (LP 679 LP 689+50);

the Urals onshore section (LP 689+50 LP 706+64).

In order to ensure safety during construction and operation of the offshore section, the distance between theparallel lines will make up 50 meters.


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The minimum distance between the parallel lines at the onshore sections of the submerged crossing wasassumed to be equal to 100 meters.

The major technical solutions for the onshore sections of the submerged crossing were developed with dueregard to the engineering, environmental and geological features of the construction area:

heterogeneous structure of cryogenic formations;

high changeability of the natural environment;

domination of saline and high ice soils;

active development of dangerous cryogenic processes.

The gas pipeline will be heat-insulated in permafrost areas.

To prevent the unacceptable subsidence of the gas pipeline in the soils with low bearing capacity,underground supports are used or the soil is replaced.

In order to secure the gas pipeline stability and rule out shifts and floating-up, the water crossing is providedwith continuous concrete weight coating. On both coasts the submerged crossing is equipped with signallights which mark the safeguard zone of the crossing.

On each coast there are two reference points for vertical positioning during the crossing construction and

operation. The reference points are installed above the 10 per cent level of high water surface.The open type crossing the coastal line will be implemented together with a package of measures to protectthe gas pipeline from natural hazards throughout the operation period. A specialized trench is designed forpipeline landfalls to ensure natural bending radius.

Electrochemical protection

All methods of trunkline laying, except for the above-ground one, ensure comprehensive corrosionprevention via protective coating and electrochemical protection.

The gas trunklines operated under the wall temperature of minus 5C do not require electrochemicalprotection in case they are not exposed to negative impacts of stray currents.

Thus, at separate sections of the gas pipeline (KP 20 Baidaratskaya CS, Yarynskaya CS KP 232) thereis no electrochemical protection. Other sections are provided with electrochemical anticorrosion protection of

various minimum protection potential values.

The self-sustained electrochemical protection system of the pipelines linear parts was arranged throughestablishing electrically insulated inserts at the inlet and outlet flowlines of compressor stations and at theoutlet of the gas pipelines connected to the gas processing facility. The insulating inserts are also used toseparate the offshore and onshore sections of the gas trunkline.

The cathode protection converters are placed in fully assembled control boxes to keep them safe from lowtemperatures, icing and snowing.

If there are no overhead 10-kV power transmission lines running along the pipeline route at the YarynskayaCS Vorkutinskaya CS section, autonomous energy converters are used as cathode protection stations.

Compressor stations

Let us address the technical solutions aimed at supplying compressor stations with the basic technologicalequipment gas purification systems, gas pumping units and air coolers.

It is projected to construct 9 compressor stations, consisting of two compressor station buildings each, alongthe Bovanenkovo Ukhta gas trunkline system route, namely:

Baidaratskaya CS (CS-1);

Yarynskaya CS (CS-2);

Gagaratskaya CS (CS-3);

Vorkutinskaya CS (CS-4);

Usinskaya CS (CS-5);

Intinskaya CS (CS-6);

Syninskaya CS (CS-7);

Chikshinskaya CS (CS-8);


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Maloperanskaya CS (CS-9).

All compressor stations (except for the Baidaratskaya CS and the Yarynskaya CS) are equally supplied withbasic technological equipment. Every compressor station is provided with modular-type piping.

Compressor stations are connected with the gas trunkline via junction points mated with the cleaningassembly. The junction point occupies a single site within the CS premises.

At compressor stations CS-3 through to CS-9 natural gas is compressed by 25-megawatt GPUs. There are

5 units (4 operational GPUs and 1 standby GPU) in each compressor station building.

Modular layout applied at CSs provides for air cooling of gas in individual gas air coolers (GAC) hooked up ingroups of six for each module. Modular GACs are installed as close to each GPU as possible.

Baidaratskaya CS and Yarynskaya CS

As mentioned before, the Baidaratskaya CS and the Yarynskaya CS differ from others by equipment andlayout.

The proximity of the Baidaratskaya CS to the submerged crossing via the Baidarata Bay as well as stringentrequirements to the temperature regime at the transit point (gas temperature should be close to 0C at theexit point of the submerged section) predetermine specific requirements to the equipment layout, first of all,to GPUs and GACs.

With due regard to these requirements, the major technological equipment in the Baidaratskaya CS buildingsis projected to be arranged in the following groups based on the functions performed:

gas treatment unit;

compression unit compressor station building;

gas cooler.

The issue of GPUs selection for the Baidaratskaya CS should be tackled with due regard to the followingparticular features of this CS:

the CS is the first linear CS at the gas pipeline, therefore its operation mode depends on gasproduction regime, which is subject to unexpected changes;

the CS is the first one to be commissioned during the stage-by-stage process of the systemdevelopment, which means that GPUs of this CS will deliver both small and big amounts of gas;

GPUs operation mode is determined by the need to maintain the required temperature in thesubmerged crossing via the Baidarata Bay under various combinations of the pipeline performanceand the number of working lines.

Therefore, for this CS it seems reasonable to assume a reduced GPU capacity of 16 megawatts with sixGPUs per compressor station building. Provided with aviation drives, GPUs will be placed in individualeasily-assembled hangars.

GACs are connected in parallel and arranged in two remote groups for better fans feeding with air.

Technological pipelines will be located above the ground at the CS being designed.

The technological scheme for gas transmission at the Yarynskaya CS Gagaratskaya CS section requires

year-round natural gas cooling down to subzero temperatures due to the permafrost soils widespread in thearea. To preserve the current status of the permafrost soils and to ensure the stability of the gas pipeline, thegas temperature at the outlet of the Yarynskaya CS should be from 0 to minus 2C.

Gas cooling to the required temperature will be performed by GACs during cold spells and by GACs followedby gas cooling stations (GCS) of turboexpander type during hot spells.

GPUs and GACs are arranged in groups at the Yarynskaya CS due to the following factors:

the ability to provide the required balance between the number of GPUs and GACs in various CSoperation modes;

the opportunity to create a unified station control system for the compressor station building and GCS.

The Yarynskaya CS provides the capability to run the CS when the GCS is either operational or non-

operational.

It is projected to utilize 25-megawatt GPUs and turboexpanders with 40 million cubic meters in dailyperformance at the GCS of the Yarynskaya CS.


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Foundation design

As a rule, a specific temperature regime sets under each facility once it is constructed. It depends on thepeculiarities of the construction concept and changes the soil foundation if compared to the tundra soils. Thetemperature regime is measured by average monthly temperatures in the facilitys foundation.

Consideration of thermal effect on the soil foundation calls for the creation and maintenance of a certaintemperature regime in the foundation throughout the operating period.

In order to reduce the direct technogenic impact on structurally unstable permafrost soils, a package ofconstructive measures was designed to preserve the natural state of soils under facilities:

arrangement of a filling at least 2.0 meters thick under the construction site;

construction of a cold ventilated underground;

creation of heat insulation shields made of effective insulants;

application of various devices intended for regulating soil temperature regime (heat stabilizers).

Ventilated undergrounds are built under major production facilities with cargo loading grounds and platforms,if necessary.

Considerable labor saving is achieved through application of complete-packaged devices, quickly erected

buildings, factory-framed light-weighted metal supporting and enclosing structures, light foundations made ofrolled metals.

At the sites with permafrost soils piled foundations consisting of steel pipes are installed in provisionallydrilled wells with the larger diameter than that of the piles and filled with compo. Piles are loaded only afterhaving frozen into the foundation soil. A rolled-metal grill is laid above the piled foundation.

In conclusion, it should be emphasized that Gazprom has been working in the Arctic for over 30 years now.The Company has accumulated invaluable experience in utilizing gas production and transportationtechnologies in a harsh environment. Thus, there is no doubt that the Bovanenkovo Ukhta gas trunklinesystem, being a large-scale and unique project, will be successfully executed.

3. transmission - major technical solutions applied during bovanenkovo

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