Review Article

Main Factors of the Offshore Platforms Impact on the Environment

Konstantin G Berezhnoy* and Sergey V Verbitskiy

Offshore Technologies, State Marine Technical University of Saint-Petersburg, Russia

Submission:February 10, 2020; Published:June 26, 2020

*Correspondence author: Konstantin G Berezhnoy, Offshore Technologies, State Marine Technical University of Saint-Petersburg, Russia

How to cite this article:Konstantin G B, Sergey V V. Main Factors of the Offshore Platforms Impact on the Environment. Oceanogr Fish Open Access J. 2020; 12(1): 555826. DOI: 10.19080/OFOAJ.2020.12.555826

Abstract

The paper considers the main aspects of offshore platforms impact on the environment and qualitative assessment also was made. This article provides a thorough introduction to the analysis of the main systems and components that could have the most significant impact. These include hull, mooring systems, marine power plant and its systems, drilling equipment. The following types of the offshore platform impacts are considered: on the atmosphere, on the subsoil during the well’s construction, on the hydrosphere, as well as on flora and fauna. Based on listed above pollution levels for flora and fauna, atmosphere and water, it can be stated that the considered platforms components in the normal operation conditions practically do not have negative impact on the environment. The greatest but also acceptable impact on the environment could have energy and drilling complexes component. This conclusion applies to the accident free offshore platform operation in compliance with all the marine activities governing rules, so is for the equipment installation that meets all the requirements for its technical condition.

Keywords:Environmental impact, Offshore platforms, Emissions into the atmosphere, Emissions into the hydrosphere, Impact on flora and fauna, Drilling complex impact, Impact assessment

Introduction

This article discusses the modern types of offshore platforms for exploration and production drilling: jack-up floating drilling rig (JFDR), a semi-submersible floating drilling rig (SFDR) and a submersible type platform. Much attention was directed to the analysis of the main systems and components, which, from the authors’ point of view, can have the most significant impact on the environment. These include hull, mooring systems, ship power plant and its systems, drilling equipment.

The following types of impact are considered:

• Exposure to the atmosphere, primarily due to exhaust emissions from platform equipment.

• The impact on the subsoil during the wells construction, mainly due to the hole boring, as well as with the discharge of waste drilling mud (WDM) and drill cuttings (DC) in emergency situations.

• The impact on the water, primarily due to the wastewater discharge during the platform equipment operation.

• Impact on flora and fauna caused by energy, light, noise, electromagnetic and radiation types of pollution due to the operation of equipment and electrical devices of platforms.

The specificity of negative anthropogenic pollution is that it is usually small (on a planetary scale), but it is continuous, chronic, and the corresponding anthropogenic pollutants tend to gradually accumulate in living and inert components of natural ecosystems and easily spread over long distances forming background fields of such pollution in the marine environment.

Hull and Topsides

The platform, located in the marine area, is a disturbing factor for fauna and flora. The hull, as a foreign object with significant visibility in the underwater part, for marine life, and the topsides/structures of upper works for birds can disorient and frighten. The Arctic regions are characterized by the polar nights and days. Drilling operations will mainly be carried out during the polar day. In this period, the visibility of the illuminated object is significantly less, but there is also a disorienting effect on migrating birds. Illuminating equipment can visually attract birds who choose platforms for a short stop, and for these purposes, birds prefer protruding, highest elements: masts, cargo cranes, rig, etc.

The effect on the flora is due to the spread of foreign plants and microorganisms from the hull fouling. Even though in the northern regions fouling by plants and microorganisms is negligible, laying-up and/or platform repair can be carried out in the southern regions, where these processes are much faster. Moving structures from the southern to the northern regions can simultaneously transfer plants and microorganisms along with the fouling layer, which will have a negative impact on the flora and fauna in the areas of operation. This effect is characterized as extremely insignificant, but still takes place. When designing platforms, it is recommended to specify measures to counteract fouling processes.

The applied protection methods and materials should be selected considering the minimal impact on the environment directly from them. Iron oxide, manganese compounds, nitrogen dioxide, carbon monoxide, inorganic dust, gaseous and insoluble fluorides enter the atmosphere while performing repair work, during the work of the welding station. Iron oxide and abrasive dust enter the atmosphere by mechanical metal working.

Mooring System

A hoist and lifting device consisting of support columns with shoes and launch-and-recovery system is used to hold the JFDR at the operating point. The support columns are partially buried in the bottom soil. Both when setting to the operating point and when removing, there are processes of agitation and deformation of the seabed. Cylindrical support columns are also an obstacle to the fish movement. Marine life can be physically damaged when it collides with them, although this is extremely unlikely.

The supporting columns rise significantly above the hull during transportation and can attract birds for short stops without having any impact. Collisions are unlikely, but still possible.

There are 3 types of mooring and positioning systems of SFDR [1]:

• Anchor mooring system (AMS) - using anchors and anchor lines.

• Dynamic positioning - using a propulsion system and thrusters.

• Composite - with the use of the two above systems. AMS has an effect fundamentally like the impact on the environment of the hoist and lifting device:

• Anchors act on the bottom soil like supporting columns, causing it to stir up and plow. The area of AMS impact can be significantly larger compared to the area affected by the JFDR supports, but it is still assessed as insignificant. This is because, when hauling the AMS lines, there is a plowing site, when the anchor furrows the seabed before engaging in soil.

• Marine life, as indicated for support columns, may be encountered and damaged by anchor lines. The likelihood of such a case also remains extremely low.

• Anchor lines passing through glues and anchor winches can also carry lubricant particles, the volumes of which are not significant, but nevertheless fall into the water while the platforms normally operate.

Dynamic positioning system originates underwater noise due to the operation of the propellers. The noise of the propellers at certain frequencies attracts marine inhabitants, which, in turn, can swim to the thrusters quite close to the point of contact with them, which lead to injury.

Ship power plant

The main impact from the ship power plant (SPP) is the exhaust emissions. Exhaust gases are products of oxidation and incomplete combustion of hydrocarbon fuels. The amount of pollutants emitted into the atmosphere is determined by the large-scale emission and the composition of the exhaust gases, which directly depend on the power of the SPP and type of the fuel. Diesel generators of diesel fuel powered SPPs are first a constant source of atmospheric pollution: nitrogen oxides, soot, sulfur dioxide, carbon monoxide, benzapyrene, formaldehyde, kerosene is emitted while of diesel generators operate [2]. In addition, operating diesel generators are a source of thermal, noise and vibration effects on the environment. Noise and vibration effects are transmitted to the marine environment and atmosphere through the platform hull and free air spaces and first affect the marine fauna.

Exhaust gases emissions are a predictable phenomenon, and the volume of emissions is subject to compensation payments for the damage to the environment [3]. The energy schemes used in ship installations and their operating modes will change significantly with respect to the use of high-sulfur heavy grades fuel in the SPP due to the fact that the amount of sulfur oxides in the exhaust gases is directly proportional to the sulfur content in the fuel: in this regard, priority is given to such installations, in which the harmful effect on will be minimal due to the high energy efficiency.

In terms of the environmental cost of pollution damage from the operation of different SPPs gas turbine generators have shown a significant advantage over diesel engines with a lowspeed engine. Thus, the environmental damage of the former is approximately 5% of the latter. In addition, dual-fuel SPP that can be operated both on diesel fuel and gas have recently become widespread. The use of gas has a positive effect on the amount of sulfur emissions into the atmosphere. Therefore, many marine engines turn to the consumption of NGV fuel [4].

The boiler plant uses the energy of fuel burned in its own furnaces, electric energy (electric steam boiler) or the utilized heat generated in other plants (waste heat boilers). Purified boiler water may be discharged into the aquatic environment at a temperature higher than sea water. The thermal effect is regarded as insignificant. The system for fuel and oil loading, storing, cleaning and supplying includes the following equipment as well: separators and transfer pumps. Pollution of sea water is possible in case of emergency, leaks. Hydrogen sulfide and hydrocarbon vapors enter atmospheric air when flammable liquids stored. Hydrocarbons in the form of vapors and leaks can be released when pumping diesel fuel or oil due to leaks in pipeline connections. In addition, the equipment of the system is a source of noise and vibration impact.

Solid Domestic Waste

While the facilities under consideration operate and, in the crew’s, vital activities, solid household waste is generated, including [1]:

• Scrap metal (pipe trimming, broken tool).

• Wooden waste (packaging and fixing materials).

• Plastic packaging material.

• Mixed garbage (worn whetstones, welding electrodes, nails, steel wire, nylon ropes, etc.).

The household garbage amount depends on the number of personnel and, according to some data, is about 0.002(m3/ day)*N(people). Food waste also depends on the number of employees and is about 0.003(m3/day) *N(people) [5]. Solid industrial and household waste is sorted. Most of them are delivered ashore by support vessels. Part of the waste not taken ashore is incinerated kitchen waste, garbage from accomodation, some medical waste, as well as oil filters, oiled rags, etc. Wastes from the platforms are transferred for processing and/or disposed of in landfills ashore. A statistical report on the volume of waste is compiled and compensatory payments are made based on the above at the end of each year [3].

Drilling Equipment and its Systems

Drilling wastewater collection system is designed to collect and localize process leaks and spills of drilling mud and drilling wastewater. A special drainage system is provided for collecting and discharging wastewater at the sites of the drilling complex, which utilized water used to flush the drilling equipment, rainwater from contaminated sections of the drilling module, spills of the drilling fluid and/or chemical components during its preparation. The collected wastewater enters the accumulation tank of drilling wastewater, equipped with mixing equipment, and is pumped into a special well. Drilling cutting waste are also collected by the drainage system of the drilling complex and sent ashore through the supply vessel.

One of the assessment option of the impact on sea water state due to well drilling is the forecast of hydro chemical regime changes within the designed facility influence zone caused by the discharge of treated domestic wastewater and normative clean water from external cooling circuits. The possibility of discharging wastewater into a water body is determined while meeting the normative permissible values of harmful substances in the water of the water body in the control site, taking into account the existing hydrological and hydro chemical characteristics of the reservoir and the qualitative characteristics of the discharged effluents.

The circulation system of the drilling rig is intended for preparation, cleaning, regulation of the properties and circulation of the drilling fluid, which ensures the removal of cuttings and power to the downhole motor and drill bit. Drilling mud cleaning as one of the most important operations in modern drilling (the entire well construction process depends on its effectiveness) is implemented in a wide variety of ways. To clean drill cuttings of heavier drilling fluids use special cleaning units.

The mud circulation system and the equipment included in it are a possible source of marine environment pollution in an emergency. In addition, inorganic dust enters the atmosphere in the drilling fluids preparation process, and its further spreading depends on wind. Drilling fluids are used to lubricate and cool a working drilling tool, bring it to the surface and separate drill cuttings, and control and regulate hydrostatic pressure in a well. The three main types of drilling compositions, in which oil products, water, or chemical synthesis products are used respectively, are most widely utilized in the practice by now.

Petroleum products (diesel fuel, oils, paraffin, etc.) are usually used as the basic components of oil-based drilling fluids (OBDF), which determines their harmful properties and environmental hazard when released into the marine environment. This was the reason for the closure on the OBDF waste disposal at sea in many countries. Water-based drilling fluids (WBDF) are currently the most environmentally preferred due to their relatively low toxicity. They are widely used now when performing offshore drilling operations.

In the 1990s a new generation of drilling fluids has appeared. Products of chemical synthesis: synthetic hydrocarbons (polyolefin and its isomers), ethers and other artificial organic substances are the basis of such brine. These solutions (SBDF) are characterized by low toxicity. The waste drilling mud storage system is applied for oil-based drilling fluids, which discharge is prohibited by the requirements of MARPOL 73/78. The system consists of storage tanks and offloading device to reload waste drilling muds from the platform to the supply vessel. Typical wastes for all types of drilling operations are drill cuttings, which are crushed rock drilled while making borehole and brought upward with a circulating fluid.

From an environmental point of view besides the dispersion of the sludge, such indicators as the content of petroleum hydrocarbons, toxic components of drilling fluids and heavy metals are critical. These indicators are the basis for the adoption of certain regulatory measures and standards for the drill cuttings from the permission of discharges into the sea to their complete prohibition. All these indicators can change greatly due to many circumstances of a technical and technological nature even when drilling a single well.

The presence of oil and oil products in the sludge is inevitable for drilling operations using OBDF. The sludge extracted from the WBDF and SBDF as a rule does not contain oil at all or only its traces. The increased content of heavy metals (in comparison with the local natural background) in solid drilling waste can occur due to the difference in the microelement composition of the drilled rock and bottom sediments in this place, as well as a result of presence in the drilling mud compositions of the barite with metal impurities and some lignosulfonates, containing iron and chromium. Almost all studies known in this field show that trace metals in sludges are in insoluble form (usually in the structure of the crystal lattice of minerals) and their content (except barium) varies within the natural variability of the geochemical background of trace elements in bottom sediments.

Environmental regulations adopted in many countries prohibit the discharge into the sea of sludge polluted by OBDF in any situation but allow under certain conditions such discharge for sludge after WBDF and SBDF using. In this case several requirements for the sludge composition and discharge areas should be observed. In particular, the amount of drilling fluid residues in the discharged material should not exceed 1%.

Discharge of sludge into the sea usually causes the following main negative effects:

• Increased water turbidity and disruption of the planktonic and benthic filtering organism’s activity.

• Physical effects on bottom organisms and changes in their existence conditions.

• Rearrangement of the species structure of bottom communities in case of prolonged discharges.

If sludge discharge into the sea is prohibited, then it should be taken ashore, or pumped back into the reservoir with flushing fluid.

Conclusion

In a qualitative assessment of the environmental impact of equipment, systems and components of platforms, the main attention was paid to such criteria as the level, duration and geographical extent of the expected impact in the spatial and temporal frame. It is known that to assess the impact on flora and fauna under design the Sakhalin shelf projects, four gradations were adopted [6]:

• Negligible or no impact: no noticeable predicted environmental impacts; the impact is so insignificant that further consideration of the environmental impact assessment is not required.

• Minor impacts: affect a specific group within a genetic population/subpopulation for a short period of time (no more than one generation of affected individuals), but do not affect other trophic levels or population/subpopulation.

• Moderate impacts: affect part of the population/ subpopulation and may cause a change in the number and/ or distribution over one or several generations of the species affected but do not threaten the integrity of this population or any dependent subpopulation. Moderate impacts on the same resource superimposed on each other within a wide area are considered significant impacts.

• Significant impacts: affect the entire population/ subpopulation or species to a degree sufficient to cause a reduction in population and/or changes in distribution, beyond which natural replenishment (reproduction, immigration from areas not affected by exposure) does not return the population, or species, or any dependent population/subpopulation or species, to the previous level for several generations of the affected species. To assess the impact on the atmosphere, 4 levels of pollution can also be used: low, elevated, high and very high. Similar criteria are used to classify water quality. Based on the given levels of pollution of flora and fauna, atmosphere and water, it can be stated that the considered platform components under normal operation practically do not have a negative impact on the environment. The greatest but also acceptable impact on the environment can cause energy and drilling complexes elements. This statement applies to the accident-free operation of facilities in compliance with all standards for maritime activities, as well as the installation of equipment that meets all current requirements for its technical condition.

References

1. Saint Petersburg (2018) Rules for the classification, construction and equipment of floating drilling rigs and offshore stationary platforms, Russian Maritime Register of Shipping.
2. Emissions of pollutants into the atmosphere. Method for calculating emissions from stationary diesel plants.
3. Federal Law No. 7 “On Environmental Protection”.
4. MARPOL Annex VI to the Convention "Rules for the Prevention of Air Pollution from Ships".
5. Patin S A (2017) Oil and ecology of the continental shelf. (2^nd), Offshore Oil and Gas omplex: State, Prospects, Impact Factors, VNIRO Publishing House, Moscow.
6. Environmental impact assessment. Explanatory note. Sakhalin-2 Project, Geological Engineering Research of the South Piltun Field, 2017