슬러그 사이즈 및 WAG 비율이 CO_2주입에 의한 오일 회수능력에 미치는 영향에 대한 실험적 고찰
Experimental Analyses of the Effect of Slug Sizes and WAG Ratios on Oil Recovery by CO_2 Flooding
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초록
CO_2 공법은 사암 저류층에서 가장 널리 사용되는 회수증진법(EOR)이다. 이 기법은 이미 수많은 실험과 현장 프로젝트를 통해 그 효과가 입증되었다. CO_2 공법은 오일비중, 오일 포화도, 점성도, 저류층 불균질성, 슬러그 사이즈, WAG 비율 등의 특성에 영향을 많이 받는다. 본 연구에서는 다양한 CO_2 슬러그 사이즈와 WAG 비율이 WAG 공법의 회수능력에 미치는 영향에 대해 실험을 통해 알아보았다. 실험은 MMP(최저혼화도압력) 측정과 서로 다른 조건에서 코어를 이용한 WAG 공법 적용의 두 부분으로 크게 나눠 실행하였다. CO_2와 오일(데카인) 사이의 MMP는 슬림튜브 실험 및 상관관계 분석법을 이용해 구하였으며, 코어 실험은 직경 3.8 cm, 길이 29.5 cm의 베레아 사암(berea sandstone)을 이용해 실시되었다. 실험은 0.2, 0.4, 0.6 PV의 슬러그 사이즈와 1:1, 1:2, 2:1의 WAG 비율에서 수행되었다. 또한 연속주입공법(continuous gas injection, CGI)와 혼합공법(CGI+WAG)을 비교하기위한 실험도 실시하였다. CO_2 슬러그의 크기와 WAG 비율에 의한 영향에 대하여 살펴본 결과, 회수율(RF) 및 3차회수인자(TRF)는 0.2 PV CO_2 슬러그 사이즈에서 1:2 WAG 비율을 사용한 경우 최적임을 나타내었다.
Abstract
CO_2 flooding has been the most widely used EOR (enhanced oil recovery) method in sandstone reservoir. The method has proven its excellent effectiveness through many laboratory and field projects. CO_2 flooding is influenced by properties such as oil gravity, oil saturation, viscosity, reservoir heterogeneity, slug size, WAG ratio, etc. In this study, the effect of different CO_2 slug sizes and WAG ratios on WAG performance in WAG (water alternating gas) were experimentally investigated. The experiments are subdivided into two major sections; MMP (minimum miscible pressure) determination and WAG flooding at different conditions. The MMP between CO_2 and oil (n-decane) was determined by slim-tube method and empirical correlations. The core flooding experiments were conducted with berea sandstone cores, 3.8 cm in diameter and 29.5 cm in length. The experiments were performed using different CO_2 slug sizes of 0.2, 0.4, 0.6 PV (pore volume) and different WAG ratios of 1:1, 1:2, 2:1. The experiments were also performed to compare CGI (continuous gas injection) method with mixed method (CGI+WAG). Based on experimental observations according to the effect of different CO_2 slug sizes and WAG ratios, RF (recovery factor) and TRF (tertiary recovery factor) were the highest when using 1:2 WAG ratio at 0.2 PV slug size.
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