As part of the Nautec conceptual planning for the PM-313 gas cluster development, Nautec conducted a high level screening of CO2 disposal or sequestration options with a preliminary screening of reservoirs suitable for CO2 reinjection, injection requirements, injectivity, downhole/flow line/process metallurgy and chemical treatment options.
The end client was Malaysian state oil company PETRONAS Carigali Sdn Bhd (PCSB).
The primary objective of the study was to assess the suitable option for the CO2 The strategies which have been considered are:
- Atmospheric venting of CO2
- Produce raw gas with CO2 to the market/pipeline
- Separation and re-injection of produced CO2 into an old gas bearing reservoir
- Separation and re-injection of gas into an existing oil bearing formation
- Use of carbon dioxide for IOR processes by injecting gas as a part of a water-alternating gas scheme or a Gravity Stable Injection Scheme.
The Value Added
The quantities of CO2 to be removed and disposed of range from 200 – 500 MMscf/day throughout the forecasted life of the project, therefore venting is not considered tenable over the forecast life of the project.
There are two major alternatives namely:
- Injection of the CO2 into depleted gas reservoirs in the region, perhaps as part of the sequential development of the clusters
- Injection of gas into oil fields (green or brownfields)
From these alternatives, Nautec reviewed two available process available:
- GSGI Gravity stable gas injection whereby the CO2 is injected into the top of the reservoir thus providing enhanced reservoir energy for assisting production
- WAG or CO2 injection as an enhancement of sweep.
It is likely the GSGI and WAG process using CO2 in an oil reservoir could yield increases in oil recovery of 3 – 6% and 8 – 10% of recoverable reserves respectively.