HEAD OF TEAM	:	Prof. Dr. Johnner Sitompul
TEAM MEMBERS	:	Ucok W.R. Siagian, Annisa Sabrina, Stefanus, Michael D.M.S
OFFICIAL ADDRESS	:	Laboratory of Design Method and Process Control
Email	:	sitompul@che.itb.ac.id
EXTENDED ABSTRAct	:

 

1. INTRODUCTION

One of the most effective EOR methods is known as Alkaline-Surfactant-Polymer Flooding, because it has the synergy between solution mixture from alkaline, surfactant, and polymer. Furthermore, polymer can increase the viscosity of the solution, so mobility ratio of the injected solution decreases significantly hence the oil recovery will increase. One of an alternative popular polymer is hydrolyzed polyacrylamide (HPAM), synthesized using hydrolysis of polyacrylamide, while polyacrylamide come from polymerization of acrylamide monomer. Polymerization method to produce HPAM applies aqueous solution polymerization in order to obtain very high molecular weight for EOR. The application of biodegradable surfactant (anionic type) is very good alternative to petroleum based one considering environmentally friendly aspect in ASP. The biodegradable surfactant was synthesized from sulphonation of fatty acid methyl ester (FAME), produced from methanolysis of Palm Kernel Oil and fractionation of its FAME with C16 and C20 FAME cut.

The objective of this paper is to characterize and discuss the effect of hydrolyzed polyacrylamide (HPAM) and biodegradable surfactant formulated for the alkaline-surfactant-polymer (ASP) Flooding in Enhanced Oil Recovery (EOR). The addition of surfactant is to reduce surface tension and change the wettability so it can reduce capillarity tension in the rock. Further, the study will compare oil recovery using ASP flooding compared to SP flooding or Polymer flooding, respectively.

 

2. METHODOLOGY

 

2.1 HPAM Formulation

 

HPAM formulation was started by adding acrylamide (13.94 g) and sodium carbonate (6.24 g) to aqua dm (200 mL) in a beaker. The solution is then purged by nitrogen for about 30 minutes. After the purging had been completed, potassium persulphate (0.2 g) was added into the solution as an initiator. The temperature reaction was controlled at 80 ^oC and stirred for 2 hours in nitrogen atmosphere. After that, precipitation of HPAM was carried out by adding methanol and followed by drying the precipitate in the oven at around 50 ^oC for about 1 hour.

 

2.2 MES Formulation

The formulation was aimed to calculate composition to produce surfactant. Methyl ester (0.35 mol) was filled into 500 ml three-neck flask and then sulfuric acid (0.39 mol) was fed drop by drop into the flask. The solution was mixed and stirred using magnetic stirrer and maintained at temperature of 65 ^oC for about 1.5 hour. The flask temperature was slowly decreased to 50 ^oC, and then methanol 40%-w/w was added into the mixture. NaOH 30%-w/w was added for controlling pH between 5 to 6.

 

2.3 Phase Behaviour Test

The test is to determine the optimum composition of ASP mixture. Certain volume of ASP was filled into a 100 ml beaker glass. Diesel oil was added to the beaker and then the solution was mixed until homogenous solution was achieved for testing the phase behavior. The mixed solution was poured into a vessel and the vessel was covered up for about 60 minutes. The micro-emulsion formulation was checked and then the composition of ASP was determined with the optimum micro-emulsion solution. The optimum composition was determined by the highest volume of micro-emulsion occurred during addition of ASP into the oil-water mixture as visual examination showing three-phase behavior.

 

2.4 Viscosity Test

Viscosity test of injection solution was carried out using Brookfield Viscometer by setting the viscometer into zero (Autozeroing viscometer). The injection solution was placed into a 500 ml beaker and ready for testing in the Brookfield Viscometer.

 

2.5 Core Flooding Test

The core flooding test was shown in Figure 2 below. The core sandstone with the proportion of 35% quartz sand and 65% cement (??? ) was prepared and the core was heated in the oven for about one day and then its weight was recorded. The core was saturated with oil SO IT WAS NOT PRESATURATED WITH WATER? for 8 hours and the core weight was measured after being saturated by oil. The saturated core was placed into the holder and the injection solution sample was flowed into the core by turning on the pump in the storage vessel. The oil recovery (OOIP) collected in the flask was determined after flooding test had been completed.

 

 

3. RESULTS AND DISCUSSION

 

3.1 HPAM and MES Synthesis

Table 1 shows results of various HPAM produced from hydrolysis of PAM. The molecular weight of HPAM-1 was measured to be 2.77 x 10⁷ dalton (g/mol) at temperature 80 ^oC using Mark-Houwing correlation. The average molecular weight of polymer for EOR is usually in the range of 2×10⁷ to 1×10⁸ dalton for EOR (Sorbie, 1999). The HPAM-2 has lower molecular weight (10.5 x 10⁶) despite the same temperature condition, because in this HPAM-2 synthesis addition of initiator was done before conducting nitrogen purging. Hence, this made the oxygen still trapped in the solution hindering termination process during growing of polymerization chain reaction. HPAM-3 has the lowest molecular weight. For HPAM-3, the temperature of production was quite high, i.e., 95 ^oC, which showed the increase of temperature result in decrease of degree of polymerization during synthesis of HPAM, so the molecular weight obtained was lower, 2.1 x 10⁶ dalton compared with HPAM-1.

Tabel 1 Molecular weight of HPAM polymers

Polymers	Molecular Weight (Dalton)
HPAM-1 (80oC)	27.7 x 106
HPAM-2 (80oC)	10.5 x 106
HPAM-3 (95oC)	2.1 x 106

Note: HPAM-2 using initiator fed before nitrogen purging

Surfactant formulation was validated using the analysis of acid number and surfactant screening test. Surfactant screening test is being used to check the criteria in EOR with phase behavior and core flooding test. Acid number test is the total amount of mass KOH in mg used to neutralize 1 g fatty acid in sample. In MES reaction the methyl ester can be hydrolyzed into fatty acid and produce carboxylate sulphonate as a product. Hydrolysis and side product cause the acid number to increase. Surfactant that was produced had acid number below 1%. As the acid number of MES quite low, most of the products obtained in these experiments were MES’s.

 

3.2 Core Flooding Test

Results of core flooding test are shown in Table 2. Note that samples 1, 2, and 3 are only polymer flooding, surfactant flooding and SP flooding, respectively. Further, samples 4 and 5, were injected with similar concentration of MES and Na­₂CO₃, while sample 4 has lower concentration of HPAM compared to sample 5. It can be seen that the ASP flooding increased the oil recovery. Oil recovery in EOR is usually around 10% to 30% OOIP, while the result of ASP showed comparable results, with OOIP between 12.8% to 23.5%. From all the samples, sample 5, ASP Flooding with large amount of polymer, has the highest OOIP. Further, the addition of alkaline with higher amount of polymer in the injection fluid produced higher oil recovery. This is because the increase of polymer concentration would then increase the viscosity of injection fluid and better sweep oil in the core. The highest oil recovery from ASP flooding has resulted in 23.53% of original oil in place (OOIP).

Table 2: Comparison of OOIP for Polymer, Surfactant, ASP flooding test

Sampel	Injection Fluid	% OOIP	Pressure of injection(psig)
1	HPAM 2800 ppm	14,89%	100
2	MES 0,5%	14,89%	27
3	HPAM 2800 ppm, MES 0,5%	17,65%	82
4	HPAM 2800 ppm, MES 0,5%, Na­2CO3 200 ppm	23,53%	100
5	HPAM 1000 ppm, MES 0,5%, Na­2CO3 200 ppm	12,82%	52

Note: MES and Na₂CO₃ in %-wt

With regard to core flooding analysis, it shows that ASP flooding produced the highest oil recovery compared to SP flooding or polymer flooding which give promising application in the field for EOR.

 

4. CONCLUSIONS

The synthesized HPAM has the molecular weight of 27.7 x 10⁶ dalton, which is suitable for EOR application and has been tested for phase behavior and further for ASP flooding. Reaction temperature of HPAM affected the molecular weight of the product. The increase of HPAM concentration apparently increased the sweep efficiency and then improve the oil recovery. Alkaline decrease the viscosity of injection fluid and it is useful during fluid injection start up so it can flow easier into the reservoir. The effect of MES concentration in phase behavior increased and then decreased after reaching the CMC. Core flooding analysis showed that ASP flooding gave higher oil recovery compared to SP flooding or polymer flooding. The highest oil recovery from ASP flooding has resulted in 23.53% of original oil in place (OOIP).