The Potential of Crab Chitosan Polymer as EOR Injection Fluid

The abundant availability of crab shell waste in Indonesia is still not optimally utilized. Crab shell contains chitin that can be processed into chitosan. Chitosan polymer can be developed to be utilized on Enhanced Oil Recovery. The objective of this study is to measure the amount of biopolymer adsorption potential of crab shell on sandstone both statically and dynamically, in order to obtain oil recovery potential by using crab shell chitosan as injection fluid. Method of this study is categorized as experimental research through direct observation inside a laboratory. The utilized biopolymer in this research was chitosan made from crab shell. Biopolymer solution concentrations in this research are 5,000, 10,000, and 15,000 mg/L and the formation water salinity levels were at 10,000 and 20,000 mg/L. The research was conducted by using variations of formation water compounds namely NaCl and MgCl2. The research conducted consists of viscosity, transmittance, and adsorption measurements on biopolymer and water formation salinity concentrations. The sand pack flooding was conducted to observe oil displacement by selected formation water and chitosan solution. After conducted viscosity test, solution with the highest viscosity levels were chosen as driving fluid in sand pack flooding. The solutions are N2R3 samples which are crab shell chitosan solution with formation water containing NaCl with salinity level 20,000 mg/L and chitosan concentration of 15,000 mg/L. The viscosity value of the sample was at 1728.67 cP. Conclusion: Crab chitosan with 15,000 mg/L concentration, 20,000 mg/L salinity, and viscosity value of 1728.67 cp can be optimally utilized in sand pack flooding by providing incremental recovery factor of 10.27%.


Introduction
The extensive production level of oil wells, especially in the primary and secondary recovery stages, lead to the decline of oil production due to weakened natural driving force, which leads to lower oil production rate towards the surface [1].Based on that, an advanced production stage, such as Enhanced Oil Recovery (EOR) is vital.One of the most used methods is polymer injection [2].Polymer injection is one of the most important part due to its ability to increase water viscosity, lower mobility ratio, and enhance sweep efficiency and recovery factor [3,4].During polymer injection implementation, mobility ratio of driving and driven fluids will be improved and oil sweep efficiency will be increased [5].The consistent development of polymer injection is evident by the development of biopolymer as injection fluid with numerous advantages such as relatively obtainable and abundant materials availability in the nature [2], strong resistance at high temperature and salinity level, and also its non-toxic nature [3,6].The most common polymer used as injection materials are synthetic polymers such as polysaccharide and polyacrylamide [7].Polysaccharide polymer can be presented in the form of chitosan.One of the most commonly used biopolymers is biopolymer-chitosan generated from chitin deacetylation [6].Polymer is a compound consist of large molecules or macromolecule with high number of repeated subunits [8].Polymer, also known as macromolecule, is a very long simple molecule structure consists of simple and small chemical units.These monomers can form linear or long chain or interconnection three-dimensional tissue [9].Polymer injection refers to activity of mixing polymer into injection water to increase injection water's viscosity level [10,11].Currently, polymer injection faces a number of challenges such as the utilization of synthetic polymers that cannot adapt to high salinity, high temperature, and mechanical degradation.The consistent development of polymer injection is evident by the development of biopolymer as injection fluid with numerous advantages such as relatively obtainable and abundant materials availability in the nature [2], strong resistance at high temperature and salinity level, and also its non-toxic nature [3,12].Biopolymer is a natural polymer which mainly composed of polysaccharides obtained from living things [3,13].Polysaccharide as main material of biopolymer is abundantly available in the nature [2].One of the utilizable biopolymers is biopolymerchitosan produced from chitin deacetylation process [12].Chitosan is a unique biopolymer, which would become cationic with positive charge in acidic solution, and will become sediment in alkali solution.Chitosan does not dissolve in water but it can be dissolved in acid, contain relatively high level of thickness when dissolved, and most of its reaction characteristic is chitin characteristic reaction [14].Chitosan is the second abundant polysaccharide compound after cellulose.It is an alkali and non-toxic polysaccharide, easily biodegraded, environmentally friendly, and relatively affordable [15].Chitosan is resulted from chitin deacetylation of a hydrolysis process on alkali solution [12].The difference of chitin and chitosan is located on the level of nitrogen.If it is more than 7%, it is categorized as chitosan, but when it is less than 7%, it categorized as chitin [12].The general formula of chitosan is C6H11NO4 or (1,4)-Amino-2-Deoksi-β-D-Glucose.Chitosan is a white yellowish solid shaped, generally dissolved on organic acid, and polyelectrolyte [15].The biopolymer chitosan structure can be seen in the following Figure 1.
Figure 1.Chitosan compound structure [16] The formation of cross-links in chitosan can improve the characteristics of chitosan such as organic solvents or water solubility, adhesive ability, bacteriostatic and complexing effects.Chitosan can absorb metal ions, anionic polysaccharides, and enzymes.

Methods
In this study, the data used were primary and secondary data where the primary data was obtained directly from measurements and observations during testing in the Enhanced Oil Recovery laboratory while the secondary data was obtained from previous test results obtained from a literature review.The characteristics tested were compatibility, density, viscosity, and adsorption and application of crab polymer injection to oil using sandpack flooding.
The concentrations of the biopolymer solutions in this study were 5,000, 10,000, and 15,000 mg/L and the salinity of the formation water was 10,000 and 20,000 mg/L A compatibility test was carried out to determine the possibility of new precipitates from the biopolymer solution made [17].Compatibility measurements were carried out using a spectrophotometer to determine the transmittance value of the solution.Transmittance is a value that indicates the amount of light that can be transmitted.The transmittance measurement was carried out after it was known that the solution made had no precipitate.The next test is the measurement of viscosity which is carried out using an Ostwald viscometer.Next, the adsorption test was carried out using the static method.This is a way of measuring the adsorption of a solution on rock by mixing the two under static flow conditions [18] using sand of 40 and 60 mesh as adsorbate.Measurements were carried out at room temperature for 7 days to reach an equilibrium state [19].After that, the polymer solution was separated from the sand by filtering and then the amount of absorbent was measured using a spectrophotometer [20,21,22].
The final test is the sandpack flooding test.Sandpack is made using acrylic material with a size of 20 cm x 5 cm x 3.3 cm.60 mesh of sand is inserted and compacted into the sandpack and connected to a syringe pump using a hose.The sandpack flooding test was carried out to see the results of oil displacement by formation water and crab chitosan polymer solutions that had been selected through a viscosity test.The solution with the highest viscosity was selected as the displacement fluid in sandpack flooding [23].

Results and Discussion
The tested characterizations are compatibility, density, viscosity, adsorption, and chitosan implementation to drive oil using sand pack flooding.After conducted viscosity test, solution with the highest viscosity level was selected as driving fluid in sand pack flooding.The solution is the N2R3 sample, which is a crab chitosan solution with water formation salinity that contains NaCl of 20,000 mg/L and chitosan concentration of 15,000 mg/L with viscosity level of 1728.67 cP.The sand pack flooding test was conducted to observe oil driving process by the selected formation water and chitosan solution.Bulk used in this research is a previously designed sand pack made from acrylic with a measurement of 30 × 10 × 0.33 cm.The sand pack size can also be categorized as bulk volume of 330 cc.The first injection conducted was a brine injection as much as 1.3 times of the bulk volume.The intention of the injection is to perfectly saturate sand pack pores.From the injection process, the total injection volume was at 472.2 mL and brine produced from the sand pack was at 324 mL, which means that the sand pack volume pore was at 148.2 mL.
Oil injection was further conducted to drive brine out of the sand pack, which then lead to oil filling the sand pack pores, with injection level of 112.3 mL and the discharged brine of 92.5 mL.The discharged brine volume can also be said as initial production volume to measure oil residual saturation.With the volume showing 92.5 mL, the oil residual saturation should be at 62.2% and water residual saturation at 37.58%.The condition is assumed as reservoir condition, because oil can fill more than 60% of the available rock pores.The porosity of the sand pack at 44.91%, is categorized as high because the sand used in the sand pack is homogenous without the existence of cement, which enable more pores on the sand pack.Through the water flooding, we acknowledged the production level of 78.From Figure 2 we can see that oil production level is improved from 78.5 mL to 88 mL, which means that there is production enhancement of 9.5 mL.The oil production volume was converted into percentage as seen in the following Figure 4 and Table 2.   Based on the results, there is an improvement of oil production by implementing polymer flooding instead of water flooding with a percentage of 10.28%.

Conclusion
The selected crab chitosan sample with 15,000 mg/L concentration, 20,000 mg/L salinity levels and viscosity value of 1728.67 cp is the selected chitosan with that can be optimally utilized in sand pack flooding with incremental recovery factor at 10.28%.Based on these results, we can conclude that chitosan polymer possesses high potential to be utilized in Enhanced Oil Recovery process.
5 mL and chitosan 1239 (2023) 012038 IOP Publishing doi:10.1088/1755-1315/1239/1/0120384 flooding produce 9.5 mL of production.Based on those results, the total oil production on sand pack flooding was at 88 mL, as illustrated in the following Figure 3.

Figure 2 .
Figure 2. Oil production volume with sand pack flooding

Figure 3 .
Figure 3. Recovery Factor Percentage with Sand Pack Flooding

Table 1 .
Results of viscosity measurement of crab chitosan solution with NaCl

Table 2 .
Sand pack flooding production results