摘要
When low-salinity water containing sulfate ions is injected into carbonate reservoirs, rock dissolution and in situ precipitation occur, altering rock permeability and wettability. Particularly, when barium ions are present in formation water,they react chemically with SO;, and BaSO;is precipitated. These reactions can cause a serious impact on the efficiency of enhanced oil recovery（EOR）. Therefore, the main purpose of this study was to identify EOR efficiency induced by lowsalinity waterflooding（LSWF） when Ba;is present in carbonate reservoirs. From the experimental results, it was confirmed that the permeability calculated by the measured pressure difference was improved because of rock dissolution predominating over in situ precipitation for the case of low Ba;concentrations. In the analysis of wettability alteration through the measurements of relative permeabilities before and after LSWF, the higher Ba;concentration case consumed more SO;in precipitating the BaSO;, resulting in weaker wettability alteration due to the reduction of sulfate activity.These phenomena ultimately influenced EOR efficiency, i.e., the oil recovery was greater for the lower Ba;concentration.
When low-salinity water containing sulfate ions is injected into carbonate reservoirs, rock dissolution and in situ precipitation occur, altering rock permeability and wettability. Particularly, when barium ions are present in formation water,they react chemically with SO_4^(-2), and BaSO_4 is precipitated. These reactions can cause a serious impact on the efficiency of enhanced oil recovery(EOR). Therefore, the main purpose of this study was to identify EOR efficiency induced by lowsalinity waterflooding(LSWF) when Ba^(2+) is present in carbonate reservoirs. From the experimental results, it was confirmed that the permeability calculated by the measured pressure difference was improved because of rock dissolution predominating over in situ precipitation for the case of low Ba^(2+) concentrations. In the analysis of wettability alteration through the measurements of relative permeabilities before and after LSWF, the higher Ba^(2+) concentration case consumed more SO_4^(-2) in precipitating the BaSO_4, resulting in weaker wettability alteration due to the reduction of sulfate activity.These phenomena ultimately influenced EOR efficiency, i.e., the oil recovery was greater for the lower Ba^(2+) concentration.
基金
supported by a Grant as part of the ‘‘Development of IOR/EOR technologies and field verification for carbonate reservoirs in UAE’’ project by the Korean Government Ministry of Trade,Industry and Energy (MOTIE).(No. 20152510101980)
