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Implementation of the "zero discharge" principle for the operation and maintenance of the "Prirazlomnoye" oil field Печать E-mail


"Prirazlomnoye" oil-field (POF) is situated on the continental shelf in the southeastern area of the Barents Sea. JSC "Sevmorneftegaz" was granted the right for the subsurface use under the "Prirazlomnoye" oil-field, and is now in the process of development and coordination of pre-project and project documentation for the oil-field development in accordance with the established procedure. FRECOM Ltd. was contracted to perform the works on environmental impact assessment.

Environmental protection problems and activities require particular attention and planning though all phases of the POF development due to complex and complicated climatic conditions and outstanding sensitivity and vulnerability of the environmental media (components) - primarily of the marine biota to the expected technogenic/man-made impact in the process of the POF exploration and development, hi view of the above JSC "Sevmomeftegaz" has developed and committed itself to environmental policy, which, along other objectives is primarily aimed at the maximum reduction in the environmental impact conservation of environmental media components, sustainable use and management of natural resources.

The planned development / operation and maintenance of the oil-field rely on the construction and functioning / operation of the reliable and effective modern complex facility for oil production, which should comply with the existing legal and regulatory standards1 requirements to environmental and industrial safety. The POF development is going to be implemented with the use of one ice-resistant (sleet-proof) stationary marine/sea platform or off-shore structure (SIRSP), designed for well-drilling- production and storage of oil. and for personnel accommodation.

The produced oil is to be treated on the platform (in-situ) to comply with the export specifications (gas and water separation, and reduction in hydrogen-sulphide content). The produced oil treated for transportation is to be stored in the oil-storage facility located at the platform's base. The oil storage facility provides for the so called “wet storage” type. The oil storage facility is to be permanently filled with liquid, i.e. with oil or outboard (ballast) water. That type of storage provides for safe oil storing (exclusion of free gas). The stored oil is to be directly pumped (uploaded) in tankers (oil-carriers) from the platform caissons.

In compliance with the requirement of the Marine navigation registry no planned discharges of oil-containing water are to take place at the POF development facilities. Outboard discharges are to be limited to fire water from the volume flooding-system, water from the cooling system of technological equipment, utility-and-sanitary waste-waters after adequate treatment The present article offers a review of technical solutions on water-supply and water-disposal to be implemented in the platform design, which are aimed at both provision of the platform operational capability and implementation of the necessary technological processes and, without prejudice to the production, at provision of environmental safety and reduction in marine environmental impact.

Outboard-water system. The outboard-water system is used for the platform ballasting, pumping of water into the system of reservoir pressure maintenance (RPM), cooling of the technological equipment, drilling mud makeup, and sanitary needs. Outboard-water is supplied by the outboard-water supply pumps (five pumps with 25 % output, four main and one reserve unit) that are designed to satisfy the total demand in ballast and outboard-water during oil shipping for transportation.

The outboard water is treated by the coarse filters designed to retain/remove 98 % of solid matter particles exceeding 80 microns in diameter. To fight sea flora and microorganisms, the system is equipped with two complete units for sodium-hypochlorite water treatment натрия. Treated outboard-water is utilized for heat abstraction from the refrigerating agent (coolant), heat-carrying [heat-transfer] agent (temporary load heat exchanger), recirculation cooler of water pump-in and crude-oil systems.

Ballasting water system. Stabilized oil is stored in storage-reservoirs of the SIRSP supporting (bearing) structure. The platform (off-shore structure) provides for the system of "wet" oil storage based on constant filling of the reservoirs with water. That system is necessary to ensure stability of the base and sufficient mass load on the bottom to resist external pressures, such as ice and wave impact, as well as to prevent accumulation of combustible vapors in the storage-reservoirs.

The ballasting water system serves to maintain positive pressure in the storage-reservoirs and constant filling of the reservoirs with liquid, as well as to prevent over-pressure built-up through maintaining constant water level in the head pressure reservoir of ballasting water.
When the caisson chambers are being filled with oil the ballast water is displaced by the oil and flows into the pressure reservoir of the ballast water and then further into the treatment system for lubricating oil/petroleum 1 containing system, where water undergoes treatment prior to repeated injection into the oil-bearing horizon. During regular loading of oil in tankers the uploaded oil is displaced with the gravity flow of ballast water from the pressure reservoir of the ballast water.

Well-drilling and technological facilities. Operation of the-well-drilling and technological facilities provides for the use of sea and fresh water. Outboard-water is used to provide cooling for the well-drilling facility equipment and auxiliary diesel-generators, drilling mud makeup (preparation), and other needs. Fresh utility (technical) water is used for the preparation of drilling mud fluid, mortar (cement solution), acid and other solutions, as well as for washing well-drilling facility equipment.

Fresh-water system. The system of utility and sanitary water supply provides drinking water for consumers in the dwelling and auxiliary modules. Besides, it supplies water in the utility and sanitary fresh-water system of the well-drilling and technological facilities. The reserve of fresh water is stored in the two reservoirs for storing drinking water with the capacity of 690 m3 each, wherefrom the water is pumped into the service reservoir and goes to other consumers. Prior to the filling of the service reservoir the fresh water is necessarily mineralized and disinfected in the water treatment and preparation facility. Refilling of the fresh-water reserve tanks is to be made as directly from the water-carrier as well as from the water-desalinating plants complete with sterilizers.

System of formation water/oil-field water handling. Formation water or oil-field water extracted along with oil in the process of the oil-field development must be injected back into producing formation in order to maintain reservoir pressure, as well as to comply with the "zero discharges1' policy. Prior to repeated injection the oil-field water must undergo treatment in the system of formation/oil-field water. The system of formation/oil-field water allows reduction in free oil content in formation water and recycling of the oil separated in the treatment process. Prior to the injection into producing formation that system will also remove solid phase from the formation water to prevent plugging of producing formation.

Filter battery for the formation water utilizes nutshell as a filtering material. The filters are designed to retain/remove 98 % of solid matter particles exceeding 10 microns in diameter. The filters are also expected to reduce unbound oil concentration in the formation/oil-field water from 25 parts per million by volume to 5 parts per million by volume under normal conditions of operation.

Water injection system for RPM. Water injection is used as the main instrument for the reservoir pressure maintenance. The reservoir pressure maintenance system consists of 16 injection wells and provides reservoir pressure maintenance in producing formations through injection of mixed oil-field water, ballast water, and sea water with an admixture of chemical agents. Formation/oil-field water and ballast water make up the greater volume of the water required for the injection into producing formation. The remaining volume is supplied by the outboard-water system.

The unit assembly for fine treatment of the outboard-water is installed up-flow from the deaerator unit for removal from the treated ballast water of suspended solid matter (particles) using polyelectrolyte method. The existing unit assembly for outboard-water fine treatment functions through back-washing cycle. Already filtered and treated ballast water from the unit assembly for fine treatment is supplied in the deaerator unit. Deaerated outboard-water is mixed with oil-field water before it gets into the main water-injection pumps. The deaeration system will be used in the periods of maximum load when the injection requires the maximum consumption and the formation water is not available.

Drainage systems. To comply with the "zero discharges" requirements, the drainage systems at SERSP "Prirazlomnoye" are designed to collect all spillages of lubricating oil/ petroleum containing wastewater, contaminated rain-(storm)water and snow. All the collected wastewater is to be subsequently returned in the technological process for treatment and injection into producing formations.

The closed drainage system is specifically designed for collection of waste-water containing liquid hydrocarbons found in the technological equipment operating under pressure. The pressure vessels are drained only after pressure release. The drained liquids are transferred in the closed drainage-system reservoir wherein gases are topped to the low-pressure flare system and wastewater and liquid hydrocarbons are regularly pumped out into the maintenance separators. All liquids drained from technological and auxiliary equipment are transferred in the closed drainage-system reservoir via the closed drainage-system collectors to be further, as needed, pumped out into the maintenance separators by the pump-units of the closed drainage system depending indications/readings of the liquid level control system.

The system of open hazardous drainage is designed for collection of the oil-containing wastewater released through the drain holes in the flooring of all hazardous zones. The system collects lubricating-oil/petroleum containing wastewater from the equipment operating under normal atmospheric pressure conditions, from condensate drain trays of the equipment, and the deck wastewater flow from all hazardous zones. Water of the fire-flooding system and flushing water will be collected through the deck drain holes in the drainage reservoirs installed in all the hazardous zones. The liquids (wastewater) collected in the reservoir of the open hazardous drainage system actually make up a mixture of outboard-water, crude oik formation water, lubricating oil and chemical agents. Under normal conditions the reservoir of the open hazardous drainage system functions in the nominally empty conditions to provide maximum free volume for drainage reception.

The system of open non-hazardous (safe) drainage is designed for collection of the oil-containing wastewater released through the drain holes in the flooring of all zones. Non-hazardous effluents (waste-water) comprise a mixture of storm-water, outboard water, and lubricating oils. Storm-water effluents, water of the fire-flooding system and flushing water is collected through the deck drain holes in the drainage reservoirs installed in non-hazardous zones. The oil-containing wastewater from the non-hazardous zones is transferred by gravity flow into the tank for open non-hazardous drainage effluent that is located in the safe caisson section. As the tank is filled wastewater is regularly pumped out into the system for oil-containing water treatment to be adequately treated and subsequently injected into producing formations.

System for treatment and utilization (recycling) of oil-containing water. The water treatment system processes the following oil-containing wastewater: ballast water from the storage reservoirs used for back-washing of the filters, oil-containing wastewater from open drainage systems of hazardous and non-hazardous effluents.

Formation/oil-field water and oil-containing wastewater is not discharged overboard but is treated and repeatedly injected into the producing formation to maintain the reservoir pressure. The pre-treated oil-containing wastewater is mixed with the outboard water, then filtered and deaerated in the water processing system prior to mixing with the treated formation water and supply to the water injection pump-units.

The system of the formation water treatment has been described in the above paragraphs. The ballast water pumped out of the oil-storage reservoirs undergoes treatment to provide removal of solid matter particles, oil and paraffin prior to supply in the system of injection into producing formations. When necessary the outboard water is added to the ballast water at the input to maintain required water consumption at the output of the outboard water deaerator unit. At the last process phase the treated ballast water is transferred by the pumps of treated oil-containing water into the system of the outboard water intake before the fine treatment filters of the outboard water, where it undergoes additional filtration and deaeration and is used for injection.

System of treatment and utilization of the well-drilling waste. All the effluents (wastewater) containing drilling mud fluid are transferred for utilization at the installation for mud suspension preparation and further injection back into producing formations.

System of utility and sanitary wastewater handling. The system of utility and sanitary wastewater handling provides for collection of sewage and utility (domestic) wastewater generated by the sanitary installations and devices, galley (kitchen) and laundry equipment of the dwelling module, sanitary equipment of the auxiliary module, as well as collection of wastewater from the drainage system of the well-drilling and technological facilities. All the drained wastewater is transferred to the installation for biochemical wastewater treatment, which is located in a safe/non-hazardous zone on the caisson roof (floor). Clarified and disinfected (decontaminated) wastewater is transferred from the installation in the system of open non-hazardous wastewater.

Conclusions. The engineering solutions applied to the platform design will allow reduction in the negative impact on the marine (sea) environment. That may be achieved through the following commitments:

- compliance of all the Project participants (stakeholders) with the established requirements to the use of natural resources and environmental protection regulated by the international and Russian legislation;

- implementation of activities aimed at absolute prevention of transfer of polluting substances in the marine environment (disposal of well-drilling waste into absorption wells, "zero discharge" policy, etc.).



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