Carbon Capture Utilization and Storage in Offshore Platform

With the development of offshore oil and gas fields, more and more offshore oil and gas fields are found to have high carbon dioxide (CO2), and the carbon dioxide content of some offshore fields is up to 40%.

Especially in offshore gas fields, the high content of CO2 has a potential corrosion risk to the upper structures and pipeline. But CO2 cannot be emitted directly into the atmosphere, it is considered to be a major contributor to the greenhouse effect and climate change. Therefore, the correct separation and emission of CO2 have become the key problem to be solved by offshore oil and gas fields.

The latest assessment report of the Intergovernmental Panel on Climate Change (IPCC) also shows that to achieve the global temperature limit of 1.5 ℃, global CO2 emissions will need to be reduced by about 45% in 2030 compared to 2010, and “net zero” emissions will need to be achieved in 2050.

The CO2 produced by offshore gas fields can be buried on land or subsea. From the engineering and economic point, it is ideal to inject CO2 on land or near shore. Generally, before the exploration of the offshore gas field, the appraisal well and seismic data were limited on the sea, the geology surrounding the gas field area is clear, including the type of structure, and reservoir-cap conditions. Therefore, if inject on land or near shore, relevant exploration needs to be carried out to determine the thickness, occurrence, and distribution range of the high permeability saltwater layer and the cap layer. In consequence, CO2 in the offshore gas fields is more suitable for deep saline water storage mode.

According to the method of carbon dioxide capture, the geological storage in the saltwater layer can be divided into primary and secondary capture. Primary capture is the sequestration of carbon dioxide directly blocked by geological traps. Secondary capture means the carbon dioxide is dissolved in salt water and reservoir minerals to produce new minerals and achieve permanent storage of carbon dioxide. Secondary capture is known as mineral carbonization or mineralization and provides a potential method for achieving long-term and permanent storage of CO2.

The primary and secondary carbon capture will undergo certain steps as,

Primary Capture Treatment :

1. Capture: CO2 emissions are captured from Industrial sources using various technologies such as amine scrubbing, chemical absorption, or other capture methods.

2. Compression and Transportation: The captured CO2 is compressed to increase its density, making it easier to transport. It is then transported via pipelines or other means to the chosen geological storage site, which is often located in deep ground.

3. Injection and Sequestration: The CO2 is injected into the geological trap or formation, where it is intended to be stored securely over long periods. The geological formations act as natural containment structures, preventing the CO2 from escaping back into the atmosphere.

4. Monitoring and Verification: After injection, continuous monitoring and verification are essential to ensure the CO2 remains surely trapped and does not leak back into the atmosphere.

Secondary capture Treatment:

Pre-treatment: The captured CO2 from primary carbon capture is subjected to the pre-treatment. The pre-treatment unit is comprised of some chemical reactions to remove the impurities. The impurities are collected to the impurity area and the pure Carbon dioxide is taken to the next step. After this pre-treatment, the Carbon dioxide is carried deep into the ocean /Sea.

Injection: The purified CO2 is injected into the saline aquifers. The saline aquifers are nothing but solid rocks with millions of pores. According to science in the deep sea, the rock is always pores in nature. So this carbon dioxide fits into the porous of the rock. There are three different types of accommodation of carbon dioxide inside the pores of the rock.

If the CO2 settles between the pore spaces is termed residual trapping.

If the CO2 dissolves into the other fluids already trapped in the reservoir is termed solution trapping.

If the CO2 molecules interact with existing minerals and bind to the rock is termed a Mineral Trapping.

How does the CO2 stay underground?

A non-porous impermeable cap rock makes it impossible for CO2 to seep upwards, this caprock extends for hundreds of meters permanently sequestering the CO2 below back at the surface our monitoring system fail-safe redundancy and 24-hour surveillance ensures a safe operation for the environment and the community.

The above image is the representation of CCUS for both onshore and offshore platforms but the storage is kept deep down the sea.

Case study of storage capacity by region

The potential for carbon dioxide storage under the sea will depend on various factors such as the geology of the seabed, the presence of suitable geological formations like saline aquifers or depleted oil and gas reservoirs, and the availability of appropriate infrastructure for carbon capture and storage (CCS) projects.

The above representation of CO2 storage capacity by region. It will depend upon several factors. One case study I took for the United States.

Conservative estimates show that the US has 8.3 trillion metric tons of CO2 storage capacity, that’s enough to store the annual emissions of 35 billion vehicles for the next 50 years.