Time Lapse Measurement of Reservoir’s Parameters Change due to CO2 Injection in Parigi Carbonate West Java

CO2 injection is a process that involves injecting carbon dioxide gas into various substances or environments for different purposes. This technique, also called Carbon Capture and Storage (CCS) or Carbon Capture, Utilization, and Storage (CCUS), aims to prevent or reduce carbon dioxide emissions from reaching the atmosphere as they would affect climate change and also global warming. CCUS can also use the captured carbon dioxide for various purposes, such as enhancing oil recovery, producing fuels, chemicals, or building materials, or storing it underground or underwater. In this study, we investigated the phenomena of CO2 injection in Parigi carbonate rock from West Java. Our study involved various laboratory measurements of Parigi carbonate rock, focusing on changes in porosity due to CO2 injection. The porosity changes were observed using micro images analysis from microscope time-lapse analysis, CT-Scan, and laboratory helium porosity meter. The laboratory measurements of CO2 injection in brine water showed that the pH of the water can decrease to below 5, creating an acidic environment that induces dissolution of the pore structure. We measure the effect of CO2 injection to the Parigi carbonate samples by time lapse measurement strategy. Results of the laboratory measurements showed that the porosity increased during CO2 injection and the mass of the samples decreased during the CO2 injection process. These phenomena suggest that CO2 may induce dissolution of carbonate rock. Furthermore, the changes in porosity confirm that there is a chemical reaction during CO2 injection processes in Parigi carbonate.


Introduction
CO2 injection is a process that involves injecting carbon dioxide gas into various substances or environments for different purposes.In the oil and gas industry, this technique can be used to enhance oil recovery and reduce the emissions of greenhouse gas.By injecting CO2 into depleted oil reservoirs, the gas can dissolve in the residual oil and make it more viscous and mobile, thus increasing the amount of oil that can be extracted.At the same time, the CO2 can be stored underground and prevented from reaching the atmosphere as they would affect global warming.This technique is also called Carbon Capture and Storage (CCS) or Carbon Capture, Utilization, and Storage (CCUS).
storage.The study comprises the mineralogy of Parigi Carbonate, pore structure characteristics of carbonate, acidity of dissolved CO2 in water, and the impact of CO2 injection in pore structure of Parigi carbonate rock by time lapse analysis.

Sampling Position, Mineralogy, and Pore Structure Characteristics of Parigi Carbonate
This research used Parigi carbonate rock as its samples.The samples were collected from Palimanan, West Java, specifically from Parigi formation, a part of Northwest Java Basin with a stratigraphy column shown in Figure 2. Parigi carbonates are considered as the reservoir of hydrocarbon as there are oil seeps around the area of collected samples.They are dominated by calcite mineral and predicted as reef carbonate [5]. Figure 3 shows the location of Parigi carbonate outcrop and the collected samples.Figure 6.Scheme of digital helium porosity meter measurement [12] The ratio of pore to bulk volume of rock sample is expressed by porosity (Equation 1).Siswandani and Nurhandoko in 2016 revealed the method of porosity measurement using digital helium porosity meter based on Boyle's law which is formulated in Equation 1.The formula in Equation 1 is divided into two conditions.First condition is when the valve 1 and 2 are closed, whether in the second condition, the valve 2 is opened and it connects tubes 1 and 2, see Figure 6.These conditions are expressed in Equation 2, where the pore volume is represented by  2 and its value can be calculated using Equation 3 [12].
.= (1) (2) Effective helium porosity measurements of non-cave nor void Parigi carbonate samples have a range of 5.93 -7.28%, as shown in Table 1.The helium permeability measurements of non-cave nor void Parigi carbonate samples have a range of 10.82 -84.22 mD.The samples have a relatively high

Results of CO2 Injection
The acidity of water during the injection of water dissolved CO2 into the Parigi carbonate rock shows the low pH value in the range of 4 -5, see Figure 8a.Besides, Figure 8b clearly shows the phenomenon of dissolution after two weeks of injection time.This phenomenon causes the decreasing of rock mass during the injection process.The samples were injected using water dissolved CO2 for 2 weeks.The results clearly show the alteration phenomena caused by the injection of CO2 as well as the decreasing of the mass of the rock samples caused by dissolution phenomena.The phenomenon shown in Figure 9 indicates the time lapse changes of the pore structure during the CO2 injection process.The pore structure changes relatively wider due to the dissolution process during CO2 injection.

Conclusions
The CO2 injection in Parigi carbonate rock from West Java may have good potential in the future due to the characteristics of pore structure of Parigi carbonate.We have measured various laboratory measurements of Parigi carbonate rock, pore structure, mineralogy, and CT-Scan.This research is also including the CO2 injection effects into the porosity change of Parigi carbonate.
The laboratory measurements of CO2 injection in brine water showed that the pH of the water can be in the range 4 -5, creating an acidic environment that induces dissolution of the pore structure.We measure the effect of CO2 injection to the Parigi carbonate samples by time lapse measurement strategy.Results of the laboratory measurements showed that the porosity increased during CO2 injection and the mass of the samples decreased during the CO2 injection process.These phenomena suggest that CO2 may induce dissolution of carbonate rock.Furthermore, the changes in porosity confirm that there is a chemical reaction during CO2 injection processes in Parigi carbonate which may increase the storing capacity of CO2 in the Parigi carbonate reservoir.

Figure 1 .
Figure 1.Geology map and study area.

Figure 4 .
Figure 4. XRD spectra show the dominance of calcite mineral in Parigi carbonate.

Figure 5 .
Figure 5. Thin section image shows the pore structure of Parigi carbonate sample.
Figure 8.(a) pH measurements after 2 weeks of injection time; (b) Sample mass measurements after 2 weeks of injection time.

Table 1 .
Helium porosity and permeability measurement results of carbonate rock samples.