Arthit CO2 Membrane Optimisation to Tackle Greenhouse Gas Emission Issue
Authors: Pechvijitra Pimpisa , Watanakun Kantkanit , Assavanives Boonyakorn , Tantiviwattanawongsa Mongkol , Rakdee Sukit , Wuttikiangkaipol Eakamol , Binhayeeniyi Alawee , Ammaro Songwut 
Published: February 2023

One of the most pressing environmental concerns in the Oil and Gas industry is greenhouse gas (GHG) emissions. Therefore, PTTEP (Company A) has committed Net Zero emissions by 2050. At the Arthit field in the Gulf of Thailand, the majority of hydrocarbon loss to flare is mainly from the CO2 membrane where the permeate stream is continuously and directly emitted via the acid gas flare. To align with our company's vision, the most practical approach to reduce GHG emissions at the Arthit field is to decrease the amount of hydrocarbon loss to flare by increasing %CO2 in the CO2 membrane permeate gas because CO2 contributes to greenhouse gas emissions much lower than hydrocarbon at the same emission flow rate.

To minimize hydrocarbon loss, it is essential to maximize %CO2 in the permeate gas by optimizing the CO2 membrane performance. However, it has to ensure that the heating value of the permeate gas is sufficient for complete combustion. Thus, the more selective CO2 membrane model is required by adopting the newest technology. At the Arthit field, the new membrane product is selected as its selectivity is better than the existing models. With the new membrane, it is a challenge to further investigate the optimal configuration, specifically to the Arthit field's current operating conditions, in terms of the feed flow rate, the permeate pressure, the inlet temperature, and the sequence of the preceding dehydration unit.

The investigation to optimize the CO2 membrane is successful according to the results from the intensive trial tests as follows:"Flow Allocation Optimization" determines which CO2 membrane banks should be operated with the new membrane element product. The results indicate that hydrocarbon loss from the existing and the new membrane element models are dependent on the flow rate. Operating too low flow rate compounds hydrocarbon loss."Permeate Pressure Optimization" reveals that the lower permeate pressure results in the higher %CO2 in permeate, but the higher permeate flow. Too low and too high permeate pressures aggravate hydrocarbon loss."Inlet Temperature Optimization" indicates that increasing the feed temperature exacerbates hydrocarbon loss. It is necessary to keep the inlet temperature at the minimum, but the margin must be maintained to prevent hydrocarbon condensation."Dehydration Unit Sequence Adjustment" pinpoints that the extended cooling time attenuates GHG emissions as it reduces the spikes from the heating steps that worsen hydrocarbon loss from the high temperature.

Auspiciously, hydrocarbon loss is reduced from 4.66 to 3.58 MMscfd and from 5.55 to 4.73 MMscfd for low and high nominations, respectively. In other words, 39,000 tCO2e/year of GHG reduction is achieved. Furthermore, the revenue of 33.40 MMUSD will be gained until the end of concession.

In order to drive Company A one step closer its milestone, it is crucial to keep GHG emissions from each operating field at the minimum. Since both of the Arthit field and the Greater Bongkot South field, the other offshore gas field in the Gulf of Thailand, have a CO2 membrane unit at a processing platform, the CO2 membrane optimization project at the Arthit field can be further applied to the Greater Bongkot South field and other offshore gas fields to minimize hydrocarbon loss and ameliorate the adverse effects of global climate change.