A New Chemical EOR for Sandstone and Carbonate Reservoirs

Abstract

Abstract Recently the low salinity water flooding has been introduced as an effective enhanced oil recovery method in sandstone and carbonate reservoirs. The recovery mechanism using low salinity water injection is still debatable. The suggested mechanisms are: wettability alteration, interfacial tension reduction, and rock dissolution. In this paper we will introduce a new chemical EOR method for sandstone and carbonate reservoirs that will give better recovery than the low salinity water injection without treating sea water. The new chemical EOR fluid can be used at low concentrations and can be added to the raw sea water without treatment or softening. Low salinity water was proved to cause damage to the reservoir because of the calcium sulfate scale formation during the flooding process. These chemicals are chelating agents at high pH value such as EDTA and HEDTA. Coreflood experiments and zeta potential measurements were performed using EDTA and HEDA chelating agents added to the sea water and injected into Berea sandstone and Indiana limestone cores of 6 in. length and 1.5 in. diameter. The coreflooding experiments were performed at 100°C and high pressure. The newly introduced EOR method does not cause sulfate precipitation and the core permeability was not affected. The coreflooding effluent was analyzed for cations using the ICP to explain the recovery mechanism. The effect of iron minerals on the rock surface charge will be investigated through the measurements of zeta potential for different rocks containing different iron minerals. The oil recovery increase in both sandstone and carbonate cores was up to 23% of the initial oil in place using the new fluid system. The rock dissolution, interfacial tension (IFT) reduction, and wettability alteration were the recovery mechanism in order. The IFT reduction was due to the high pH of the newly introduced fluid. The existence of iron minerals in sandstone rocks increase the positive values of zeta potential and this will change the rock towards more oil wet. Adding EDTA and HEDTA chelating agents at high pH to the sandstone rocks containing iron changed zeta potential to be negative in which changing the rock towards more water wet.