Greener and Smarter Caisson Replacement Solution

Rising climate change concerns led the Axess Group to re-think their approach in fulfilling complex subsea lifting operations.

The upstream industry accounts for 90% of global flared gas, a recent study found, with over 300 million tons of carbon dioxide emitted to the environment annually. Associated gas from oil extraction activities are burned as part of the industry’s safety routine. Explosion may take place if the pressure and flammable gas released by pressure relief valves during production start-ups and shutdowns are not discharged.

In some cases, excess natural gas is disposed of due to lack of infrastructure to capture and transport it, thereby wasting valuable energy resource which could have been utilised for power generation and other forms of energy.

As offshore platforms remain in service beyond their intended lifecycle, caissons inevitably lose their structural integrity due to internal and external corrosion caused by the harsh environment. Fatigue cracking may sever all, or part of, the caisson, which poses a serious safety concern and may damage subsea facilities. This may result in costly production shutdown, environmental disasters and damage to reputation.

Axess Group was tasked to develop a study concept on how to safely and efficiently remove and replace caissons in the most economical way possible. As part of an asset lifetime extension project, these caissons were severely corroded, and some sections have already fallen 12m deep into the seabed. Securely lifting a 90m long and 30mt heavy caisson is crucial as the oil and gas export lines below may ignite and cause an explosion if accidentally hit.

After a comprehensive scoping study, assessment, and report, Axess has identified an advanced solution that is not only cost and time efficient, but also environmentally sustainable. An ROV Solution launched from the installation itself, as opposed to the conventional method of deploying IMR vessels, was identified as the most climate-efficient way to address this problem.

The concept is in accordance with Axess’ commitment to addressing climate change, following the 2015 Paris climate agreement to keep global warming below 2 degrees. One of our focus areas is to reduce the environmental impact of our Engineering, Procurement, Construction and Installation (EPCI) solutions, particularly in the splash zones.

Why avoid the use of IMR vessels?

Traditionally, subsea operations require the need for Inspection, Maintenance, and Repair (IMR) vessels. These offshore support vessels (OSV) are equipped with cranes, helicopter platforms, personnel accommodation, and other auxiliary equipment, to support complex offshore lifting operations.

IMR vessels cost tens of thousands of dollars a day and may vary depending on the type and size of the vessel, job scope, crude oil price, location, climate and age of the vessel. Even though they have their place in the upstream industry, this “daily vessel cost” only adds up to operational expenditures. Moreover, fuel emissions from these vessels contribute to the offshore industry’s ecological footprint.

Offshore support vessels run on advanced dynamic positioning systems to ensure reliability. Due to high safety requirements and unpredictable sea state, they generally operate on patterns whereby multiple combustion engines are running. This less favourable combustion conditions result in high emissions of exhaust gases.

A large OSV can roughly output 15,000 tonnes of carbon dioxide (CO2), 270 tonnes of nitrogen oxide (NOx) and 10 tonnes of sulphur oxide (SOx) every year. Aerosols such as black carbon (BC) are also released, which directly pollutes the air and climate.

The impact of these fuel emissions differs from one region to another due to regional differences. For example, black carbon emitted over sea ice condenses the albedo of these areas. This consequently accelerates the melting of snow and causes global warming.

Other emissions such as CO2, NOx and SOx are transported and retained in the atmosphere for a very long time, causing adverse effects to air quality, human health, climate change, ocean acidification and the imbalance of natural ecosystems and marine biodiversity.

Substituting IMR vessels with ROV solutions

Axess Group’s effort to reduce the emissions and negative climate impacts of their own and their clients’ activities led to the development of an advanced ROV Solution. Axess used two types of ROVs through the course of caisson replacement: a construction ROV (CROV) to perform the mechanical tasks, and an observation ROV, which provides real-time overview of the demolition and assembly process.

The CROV has small manipulator arms to grab and hold on to lift lines, tooling and sensors to perform mechanical cutting, advanced cameras and imaging systems, thrusters to move around and rotary table that allows the machine to work upside down and turn underneath. Operated by Axess’ engineers at a console on the platform, the ROV was able to do multiple tasks such as remove the bottom grid, anode clamp, and other parts of the caisson, connect subsea lifting gears and much more.

Key advantages of ROV solution: 

  • Reduce Costs – Removing the need for IMR vessels and personnel on board
  • Flexibility – ROVs are compact vehicles that could drive around the subsea structures, bracings and other limited access areas around the caisson.
  • Non-weather Dependent – Ability to work under extreme weather conditions that would normally prevent IMR vessels.
  • Ensure Readiness – ROVs can also be parked underwater and may be quickly deployed when the need arises.

Combined with Axess’ lean engineering method, which is according to NORSOK R-002, Annex K, High-Risk Application, the caissons were flawlessly replaced using tailor-made lifting equipment, detailed engineering and method planning, complex lifting and rigging operations and other mechanical work.

Road to low-carbon future

The ROV solution is robust, safe, and reliable in high-risk subsea lifting applications. Although reducing costs remains paramount, eliminating the need for IMR vessels also means a significant contribution to the reduction of fuel emissions. Our long-term expertise and strong understanding of the rules and regulations in offshore lifting has allowed us to develop a climate efficient solution.  

The oil and gas sector accounts for 50% of global carbon dioxide (CO2) emissions, and Axess Group acknowledges the negative effects of climate change. We are aware of the importance of moving to a greener future, so we establish and implement policy solutions that are beneficial both to our clients and to the environment.

Axess Group has started focusing on innovative technologies that improve offshore project deliveries in an environmentally friendly way. ROV solution and fabrication of custom lifting equipment are some of the tools and methodologies that have been successfully implemented to Axess’ recent EPCI projects and subsea modification assignments.

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