**1. Introduction**

Anthropogenic carbon dioxide (CO2) emissions in the atmosphere are significantly increasing and critically impacting global climate. Thus, there is an urgent need to gauge and combat its effect on global climate change. In general, the source of CO2 comes mostly from combustion of fossil fuel, natural gas stream, and industrial processes [1–5]. As stated in BP energy statistics in 2018, there were 33,890.8 MT (metric tonne) of CO2 emission worldwide and the value was driven by the high energy demand. Moreover, recently in the year 2018, the global energy consumption grew at a rate of 2.9%, which is almost twice its 10-year average of 1.5% per year that is the fastest trend since the year 2010. For natural gas, its production increased by 5.2% to 136,594 Tscf (Trillion standard cubic feet) while its consumption rose by 5.3% to 135.92 Tscf, which is one of the fastest rates of increase since the year 1984. This high demand is mainly driven by the booming Liquefied Natural Gas (LNG) industry in

China, Australia, the United States of America (USA), and Russia, accounting for the vast majority of the gains in both consumption and production [6].

Malaysia is an oil and natural gas producer and is strategically situated within the significant seaborne energy trade route and one of the largest energy consumers in Southeast Asia. Natural gas is indeed a very important commodity in Malaysia, as its effect extends far beyond the national power sector to further downstream products, the national economy, and international relationships. According to the BP energy statistics, natural gas production in Malaysia is steady at 2.56 Tscf per year, while the consumption is 1.46 Tscf in 2018 [6]. As LNG exporter, Malaysia is placed second after Qatar and has one of the world's largest LNG production facilities; Malaysia Liquefied Natural Gas (MLNG) complex that is aimed to supply the demand of their primary customer from Japan, Korea, and Taiwan [7]. There is an estimated 37 Tscf of natural gas that remains undeveloped in Malaysia's gas fields, whereby its CO2 compositions exceed 10% volumetric of the produced acid gas [8]. Most of these gas fields were not economically viable in the past due to the presence of large capacities of CO2 and are always associated with potentially high corrosion risks to the topside facilities and pipelines. The development of offshore high CO2 gas fields requires prudent strategies of CO2 separation technology in order to optimize both the capital and the operating expenses for CCS [9].

Nonetheless, Malaysia is committed to mitigating CO2 emissions and has assigned its Ministry of Energy, Science, Technology, Environment, and Climate Change (MESTECC), with the responsibility of developing the national emissions reduction plan. The commitment was to voluntary reduce the economy's carbon intensity by 40% by 2020 during the Copenhagen 2009 Climate Summit and has repledged to attain 45% CO2 emission by 2030 [10–12]. The repledge was motivated by promising results with a reduction of 33% of CO2 achieved between 2005 and 2015 [11,13]. The Government of Malaysia is gauging various mitigation plans and energy efficiency alternatives, including joint CCS feasibility study with International Energy Agency (IEA) as well as future implementation of the Energy Efficiency and Conservation policy to be tabled estimated by the end of 2019 or early 2020 [14,15]. Since its inception in 1974, Petroliam Nasional Berhad (PETRONAS), solely owned by the Government of Malaysia, is the national oil and gas company and has been entrusted with the responsibility of developing the nation's oil and gas resources. To address the CO2 emission, PETRONAS has developed its Carbon Commitment pledge to support the initiatives by promoting natural gas as low-carbon fuel and application in the power and transportation industry. This is supported by their success in building the world's first pioneer floating Liquefied Natural Gas (LNG) facility. In their enhanced Carbon Commitment 2017, all future PETRONAS's projects for CO2 containing gas field development in upstream shall incorporate CCS technologies during conceptual design stage [16].

Carbon capture and storage (CCS) is a methodology to separate CO2, then to store the CO2, commonly originating from power generation, industrial processes, and from CO2 gas fields. CCS is an offset for continued fossil fuel exploration, while at the same time achieving the targeted reduction of carbon emissions. Hence, CCS has high prospects to be one of the solutions for CO2 emission mitigation technology in Malaysia, with added advantage especially if a particular technology is suitable for deployment, has competitive cost, and has nearby storage capacity availability.

The Intergovernmental Panel on Climate Change (IPCC) report [17] has indicated that in the absence of CCS implementation, the required total cost to mitigate global climate change may escalate up to 138%. Furthermore, it is a real challenge to reach the targeted limit of temperature increase to 2 ◦C scenario and an even greater one to achieve to 1.5 ◦C based on the Paris Agreement enacted in 2015 [18–20]. To achieve this ambitious goals, various international bodies such as the Global Carbon Capture Storage Institute (GCCSI), Carbon Capture & Storage Association (CCSA), Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC), and many other prominent research centers has been established to innovate CCS technologies solutions for economically viable path for CO2 emissions reduction [21]. CCS has been recently known to play a vital role in global climate change mitigation, however, there are certain challenges that need to be addressed before its implementation. One of the main challenges recognized is the fairly high cost of the CCS technology for integration

with the existing facilities as well as for widespread replicated implementation [17,22]. Currently, the high-cost driver is highly dependent on technology maturity as well as the availability of the storage sites [23]. In terms of the CCS process, the capture stage is certainly the highest cost in the CCS chain [24]. The capture stage is generally estimated to represent 70–80% of the overall total cost for CCS chain [25–27]. Reducing the CO2 capture cost is the utmost essential phase in the CCS chain in order to be economically viable in the energy industry [27]. In this study, it focuses on the techno-economic of CO2 capture technologies suitable for natural gas field applications.

### **2. Materials and Method**

This techno-economic analysis of CCS includes a gas field model, a revenue model, and a cost model as shown in Figure 1. This analysis framework is adopted from previous work by GCCSI [28] and CO2CRC [29]. These previous studies are largely recognized and the method is used regularly for estimating CCS costs. In this study, calculation methods were adapted from the existing studies and tabulated to describe the parameters of natural gas field economic performance for different cases of CO2 capture technology. In the instance where no specific data on the subject is available, assumptions were made using comparative data. This study also focuses on the capture step as it contributes to the highest cost in CCS chain.

**Figure 1.** Schematic of the techno-economic analysis framework.

The CCS performance results for the natural gas field models are incorporated into two types of models, which are the revenue model and cost model. The revenue model comes from the value of the recovered natural gas, while the cost model is the cost of CCS, including CO2 capture, transportation, and injection for storage. The output of both models is net cash flow that is then discounted to obtain fiscal precursors comprising of Net Present Value (NPV), Internal Rate of Return (IRR), and Pay Back Period (PBP) of the project as shown in Figure 1.

Since Malaysia has not yet regulated CCS implementation in its national regulatory setting, the cost model does not take into consideration the value of incentives and credits that could be obtained for CO2 storage, which would be a potentially added economic benefit to offset cost framework [30,31]. In this study, the economic analysis evaluates a CCS project's impact by evaluating its costs and benefits to the overall economy. This techno-economic analysis compares four scenarios where the project is implemented using various CO2 capture technology options, assessing the effects, including quantifying parameters in quantitative terms.

### *2.1. Gas Field Model*

This paper investigates the cost of carbon capture from the natural gas field through a case study. In this paper, Tangga Barat Cluster situated in the PM (Peninsular Malaysia) 313 Block, as the referred case study is a typical natural gas field at water depths in the range of 60 m to 71 m, about 150 km north-east of Kertih, Terengganu offshore Peninsular Malaysia. Tangga Barat Cluster is presently operated by PETRONAS Carigali Sdn Bhd (PCSB), the upstream arm for PETRONAS that has 100% working interest. The content level of CO2 at Tangga Barat is above the gas specifications required for sales gas. Tangga Barat Cluster consists of a total of 3 producing platforms, which are Laho (LHDP-A), Melor (MLDP-A), and Tangga (TGDP-A), and a central processing platform, which is Tangga Barat (TBCP-A), while a separate riser and wellhead platform TBDR-A bridge-linked to TBCP-A will accommodate the development wells for the Tangga Barat field as shown in Figure 2. Existing gas facilities nearest to the Tangga Barat Cluster fields are the gas production and pipeline facilities of the Resak field, which is located 52 km away. The main power generation, processing facilities, natural gas compression, utilities, and living quarters is located at the central processing platform (TBCP-A). The Tangga Barat field was chosen as the gathering point for gas from the Tangga, Melor, and Laho fields based on the fact that the Tangga Barat gas volumes remain the largest along the four fields and distance is the shortest to the Resak complex. It is designed for a peak capacity of 440 MMscf/d of raw gas with an initial blended CO2 level of 37 mole% (Tangga Barat CO2 content) prior to CO2 removal. The raw gas is then processed, pretreated, reducing the CO2 content to 8 mole% to meet the specifications of the downstream sales gas process requirement from the PETRONAS gas processing plant at Kertih Terengganu [32].

**Figure 2.** Tangga Barat Development Project.

In this case study, an annual average sales gas of 220 MMscf/d with 15 years of production life is estimated [33]. CO2 storage identified for this study is situated at an underground geological storage site approximately 20 km away from the Tangga Barat fields (near the Laho and Tangga fields) whereby the injected CO2 is to be stored while ensuring there is no increase of the reservoir pressure above the fracture pressure of the storage formation [34,35]. The facilities required will be a dedicated CO2 compression platform and its associated pipelines and injection wells at the Tangga wellhead platform [34,35].
