Journal of the Korean Institute of Gas (한국가스학회지)

The Korean Institute of GAS (한국가스학회)
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Oil Production Evaluation for Hybrid Method of Low-Salinity Water and Polymer in Carbonate Oil Reservoir

탄산염암 저류층에 저염수주입공법과 폴리머공법의 복합 적용에 따른 오일 생산량 평가

  • Lee, Yeonkyeong (Dept. of Earth Resources and Environmental Engineering, Hanyang University) ;
  • Kim, Sooyeon (Dept. of Earth Resources and Environmental Engineering, Hanyang University) ;
  • Lee, Wonsuk (Korea Institute of Geoscience and Mineral Resources) ;
  • Jang, Youngho (Korea Institute of Geoscience and Mineral Resources) ;
  • Sung, Wonmo (Dept. of Earth Resources and Environmental Engineering, Hanyang University)
  • 이연경 (한양대학교 자원환경공학과) ;
  • 김수연 (한양대학교 자원환경공학과) ;
  • 이원석 (한국지질자원연구원) ;
  • 장영호 (한국지질자원연구원) ;
  • 성원모 (한양대학교 자원환경공학과)
  • Received : 2018.07.12
  • Accepted : 2018.09.20
  • Published : 2018.10.31
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Abstract

Low-salinity water based polymerflooding (LSPF) is one of promising enhanced oil recovery (EOR) method that has the synergetic effect of combining polymer injection method and low-salinity water injection method. In order to maximize EOR efficiency, it is essential to design low-salinity water appropriately considering the properties of polymer. In this aspect, the main purpose of this study is to investigate the effect of pH and $SO_4{^{2-}}$ ion which one of PDI (Potential Determining Ion) on oil production when applying LSPF to carbonate oil reservoir. First, the stability and adsorption of polymer molecule were analyzed in different pH of injection water and $SO_4{^{2-}}$ concentration in injection water. As a result, regardless of pH and $SO_4{^{2-}}$ concentration, when $SO_4{^{2-}}$ ion was contained in injection water, the stability of polymer solution was obtained. However, from the result of polymer retention analysis, in neutral state of injection water, since $SO_4{^{2-}}$ interfered the adsorption of polymer, the adsorption thickness of polymer was thinner as $SO_4{^{2-}}$ concentration was higher. On the other hand, when injection water was acidic as pH 4, the amount of polymer adsorption increased with the injection of polymer solution, so the mobility of polymer solution was greatly lowered. From the results of wettability alteration due to low-salinity water effect, in the case of neutral injection water injected, as $SO_4{^{2-}}$ concentration was increased, more oil which attached on rock surface was detached, altering wettability from oil-wet to water-wet. On the other hand, in acidic condition, due to complex effect of rock dissolution and polymer adsorption, wettability of the entire core system was less altered relatively to neutral condition. Therefore, it was evaluated that better EOR efficiency was obtained when injecting low-salinity water based polymer solution containing high concentration of $SO_4{^{2-}}$ with neutral condition, enhancing the oil production up to 12.3% compared to low-salinity water injection method.

저염수 기반 폴리머공법은 기존의 폴리머공법과 저염수주입공법의 시너지 효과를 통해 오일회수율을 더욱 증진시킬 수 있는 기술로서, 공법의 효율성을 극대화하기 위해서는 폴리머의 특성을 고려한 저염수 설계가 필수적이다. 이에 본 연구에서는 탄산염암 오일 저류층에 저염수 기반 폴리머공법 적용 시, 주입수의 pH와 주입수 내 PDI(Potential Determining Ion) 이온 중 $SO_4{^{2-}}$ 이온이 오일 생산량에 미치는 영향을 규명하고자 하였다. 우선, 주입수의 pH와 주입수 내 $SO_4{^{2-}}$의 농도에 따른 폴리머 분자의 안정성 및 흡착 현상을 분석하였다. 그 결과, 주입수의 pH와 주입수 내 $SO_4{^{2-}}$의 농도에 상관없이, 주입수 내 $SO_4{^{2-}}$가 함유되어 있는 경우 폴리머 용액의 안정성이 확보되었다. 그러나, 폴리머 용액의 정체 현상 분석 결과, 주입수의 pH가 중성인 7일 때에는 $SO_4{^{2-}}$ 이온이 폴리머의 흡착을 방해하여 $SO_4{^{2-}}$의 농도가 높을수록 폴리머 흡착층의 두께가 더 얇은 것으로 나타난 반면에, 주입수가 pH 4로 산성인 경우에는 폴리머 용액을 주입함에 따라 폴리머의 흡착량이 증가하여 폴리머 용액의 유동성이 크게 낮아졌다. 다음으로, 저염수 효과에 의한 습윤도 변환을 살펴본 결과, 주입수가 중성일 때에는 $SO_4{^{2-}}$의 농도가 높을수록 탄산염암 표면에 흡착되어 있던 오일의 탈착이 증가하여 암석의 습윤도가 친유성에서 친수성으로 크게 변환되었다. 반면에, 주입수가 산성일 때에는 용해와 폴리머 흡착의 복합적 작용으로 인해 전체 코어 시스템의 습윤도는 중성일 때에 비해 비교적 덜 변환되는 것으로 나타났다. 이에 따라 $SO_4{^{2-}}$ 농도가 높은 중성의 저염수 기반 폴리머 용액을 주입할 경우 오일 생산량은 저염수주입공법에 비해 최대 12.3% 증진되어 보다 양호한 EOR(Enhanced Oil Recovery) 효과를 얻을 수 있는 것으로 평가되었다.

Keywords

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