An Experimental Study of the Use of Silica and CNC Nanofluids for EOR by Spontaneous Imbibition
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Approximately half of the oil is still left in the reservoirs after primary and secondary oil recovery today. To increase the oil recovery from the reservoirs it is necessary to apply Enhanced Oil Recovery (EOR) Methods. The EOR methods that are currently applied are often limitied by a low cost efficiency, thus new and more efficient methods has to be developed. This is why the use of nanofluids are being investigated for this purpose. In this report the use of nanofluids for EOR purposes is investigated through spontaneous imbibition experiments using Amott cells. Silica nanoparticles and cellulose nanocrystals (CNC) are used and compared to using only low salinity water (LSW). The amount of oil produced from spontaneous imbibition experiments can be useful in predicting the oil recovery from a reservoir and thus to investigate the use of nanoparticles for EOR. Since all faces are open for imbibition in an Amott cell the flow is considered counter-current. The contact angles and interfacial tensions between an oil drop and the different fluids applied are measured to identify the mechanisms causing the increased oil recovery from adding nanoparticles. Since a high degree of aggregation of nanoparticles could result in permeability impairment and retention in a reservoir, the particle size distribution was measured in the nanofluid before and after the Amott test. The use of silica nanoparticles in this experiment led to the highest oil recovery, with an average oil recovery of 33,37 %, compared to 27,09 % and 28,35 % for the LSW and the CNC nanofluid. This might be due to the silica s ability to change the wettability towards more water-wet. This ability was verified by the contact angle measurements which resulted in a contact angle of 29,68± for the silica nanofluid, 60,06± for the CNC nanofluid and 68,57± for the LSW. The interfacial tension for an oil drop in suspension was lower for the LSW than for the silica nanofluid applied, this indicates that the lowering of interfacial tension is less important in terms of oil recovery than the wettability change. A lot of oil was still stuck on the rock after fourteen days for the CNC nanofluid, this might be due to the increased viscosity of the water. The relation between square root of time and the oil recovery from the Amott test was not linear, this might be because the flow was not strictly counter-current. Both the silica nanofluid and the CNC nanofluid showed little to no sign of aggregation throughout the fourteen days, and they are thus considered stable within this time.