Experimental Study on Optimum Half-Cycle Slug Size of Water Alternating Gas Under Tertiary Miscible Carbon Dioxide Flooding

Abstract

The effect of half cycle slug size (HCSS) on Water Alternating Gas (WAG) performance in tertiary miscible carbon dioxide (CO 2 ) flooding is experimentally investigated. Different half cycle slug size influences the fluids mobility and the contact time between the injected fluids and oil, and hence to achieve the best possible displacement efficiency, an optimum water/gas half cycle slug size could exist and deserves investigation.Coreflood experiments are performed in Berea sandstone core, from which the WAG performance, such as percent oil recovery, tertiary recovery factor, and CO 2 utilization factor are determined. The core flooding experiments are conducted at 60 and at miscible condition, i.e., at a pressure 20% above the minimum miscible pressure (MMP) of the oil sample. The experiments utilize Cottonwood Creek crude oil and artificial brines. The injection and connate brine contain 33.33 wt% CaCl 2 and 66.67 wt% NaCl with salinities of 16000 ppm (mg/L) and 30000 ppm, respectively. In every core flood test, alternate cycles of brine and CO 2 with a WAG ratio of 1:1 are injected with half cycle slug size ranging from 0.05 to 0.75 PV.The results show that for the system of interest, the optimum HCSS is 0.1 PV, in which the CO 2 usage is only 0.6 PV to reach a high tertiary oil recovery of 40.63%. An HCSS higher or lower than 0.1 PV gives lower oil recovery. When HCSS is lower than 0.1 PV, the system gives lower oil recovery because some of the gas is trapped by water and keeps staying in the core instead of displacing oil. Meanwhile, an HCSS higher than 0.1 PV results in larger clusters of CO 2 and water, thus water inefficiently controls CO 2 mobility, which makes the CO 2 -oil contact time and interfacial area for mass transfer decrease and gas breakthrough occurs prematurely.This experimental study is an essential effort to obtain better understanding the effect of half cycle slug size on WAG performance, which has never been experimentally investigated before. The understanding is critical for optimizing the WAG performance.

CO2 mobility control and sweep efficiency improvement using starch gel or ethylenediamine in ultra-low permeability oil layers with different types of heterogeneity

“…The pressure drop of CO 2 injection decreases and the pressure drop of water injection increases during the WAG process. The oscillatory behavior of pressure drop mainly caused by WAG injection is in agreement with that reported earlier (Nuryaningsih et al, 2010), which indicates that the injected water improves the sweep efficiency and the injected CO 2 improves the displacement efficiency.…”

Analysis on the Design Parameters and Evaluation of the Oil Recovery in CO2-WAG Process

“…CO2-WAG(water alternating gas)는 CO2-EOR의 대표 적인 공법 중 하나로, 오일과 CO2의 점성도 차이로 인해 발생할 수 있는 문제점을 개선하기 위해 개발되었고 (Green and Willhite, 1998) 일회수율을 높이기 위해서 주입 및 생산정의 공저압 (bottom hole pressure, BHP), 주입속도, WAG 비율, 슬 러그 사이즈 등의 주요 설계변수에 대한 최적설계 방안을 도출하기 위한 많은 연구가 진행되고 있다 (Nuryaningsih et al, 2010). Wu 등(2004) 주요인자별 영향 분석 및 결과 오일회수증진 효과 분석 및 결과…”

“…Nuryaningsih et al, 2010)에서 사용된 코어의 물성 자료를 바탕으로 설정하였다.Table 1과 같이 베레 아 사암을 모사하기 위해 모델의 공극률과 투과도는 CO2-WAG 공법의 설계변수 분석 및 오일회수율 평가…”