Determination Of The Active Soap Number And Its Application In Salager Mixing Rule For ASP Flooding

Soap number is of great importance in designing and numerical simulation of ASP flooding process.However,there is not yet any established procedure to quantitatively determine the soap number of crude oil.Soaps are the salts of fatty acids,a definition generalized here to include the salts of naphthenic acids.In this thesis,we present a method to determine the amount of“active soap”,which consists only of soap that partitions into the aqueous phase at low ionic strength and transfers into the oleic phase at high ionic strength.Two fast and accurate methods,aqueous phase potentiometric titration and two-phase colorimetric titration,were used to determine the Water Soluble Active Soap Number?WSASN?,a measure of the active soap.It is found that the water soluble active soap number?WSASN?is able to provide a reasonable estimate of the amount of active soap contained in crude oil.The partition of soap between oil and brine phases was also investigated.It is found that the partition coefficient of WSASN is near unity at optimal alkali concentration as determined by IFT measurements,a result which supports the use of WSASN to represent the amount of active soap.It is found that the phase behavior of Alkali/Surfactant/Crude oil system is a function of soap/surfactant ratio,which in turn depended on the soap number,water-oil ratio?WOR?and surfactant concentration.Therefore,designing an ASP process requires extensively time-consuming phase behavior tests and tedious interfacial tension measurements.It is found that the logarithm of optimal alkali concentration versus soap fraction for a soap/surfactant mixture followed the previously proposed mole fraction mixing rule when WSASN is used and this finding could save considerable amount of time and cost for designing an ASP flooding process.The accuracy of this improved mole fraction mixing rule is validated by investigating the phase behavior of three surfactant systems with Elk Hills crude oil and sodium carbonate.The equilibrium IFT of pre-equilibrated alkali/surfactant/crude oil samples are also measured.It is found that ultra-low IFT(<10^-2 mN/m)can be obtained near the optimal condition defined by phase behavior tests,which is consistent with the predicted results by mole fraction mixing rule as well.Moreover,equilibrated IFT of pre-equilibrated alkali/surfactant/crude oil system is almost only a function of soap fraction for phase behavior samples with different WORs and surfactant concentration.NI blend and OA blend surfactants are selected based on mole fraction mixing rule.ASP flooding tests on silica sand and formation core material demonstrate that the ASP formulation has large potential to improve oil recovery after water flooding.About 40%OOIP incremental oil recovery is obtained by injecting 0.5 PV ASP slug containing 0.3%-0.5%of anionic surfactants blend,1.0%/1.5%sodium carbonate and 0.3%HPAM followed by polymer slug and the cumulative oil recovery is almost 100%OOIP.Moreover,it is found that the breakthrough time of surfactant is delayed when the injection alkali concentration is higher,which is probably resulted from the preferential partition of surfactant/soap into oleic phase at higher alkali concentration.The importance of treatment of core material is demonstrated by conducting ASP flooding test on formation core material without treating or restoration.It is found that the incremental oil recovery is unsatisfactory and there is a severe surfactant retardation caused by surfactant adsorption.The improved mole fraction mixing rule is incorporated into an in-house developed one-dimensional,two-phase,multi-componential numerical simulator to history match the ASP flooding results.It is found that the calculated results correlated with the experimental results pretty well,which proves that the generation of active soap and its synergistic effect with surfactant are extremely important in ASP simulation.After history matching,this simulator is applied to optimize the ASP process.It is found that a good oil recovery can be achieved when the injection alkali concentration is between the optimal alkali concentration of soap and optimal alkali concentration of surfactant.To summarize,a novel method to design an ASP process is proposed in this thesis and the findings will be beneficial for design and simulation of ASP flooding process in the field.