Effect of Surfactant Structure on Phase Behavior of Alkylxylenesulfonate/ Crude-Oil/Brine Systems
- T.A.B.M. Bolsman (Koninklijke/Shell Laboratorium, Amsterdam) | G.J.R. Danne (Koninklijke/Shell Laboratorium, Amsterdam)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- January 1986
- Document Type
- Journal Paper
- 53 - 60
- 1986. Society of Petroleum Engineers
- 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.5.2 Core Analysis, 5.2.1 Phase Behavior and PVT Measurements, 1.12.1 Measurement While Drilling, 4.1.2 Separation and Treating, 2.5.2 Fracturing Materials (Fluids, Proppant)
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One of the major criteria for designing surfactants for micellar flooding istheir effectiveness in stabilizing a middle-phase microemulsion under theconditions of the candidate reservoir. We studied the performance of linearalkyl-o-xylenesulfonates (Enordet LXS) with performance of linearalkyl-o-xylenesulfonates (Enordet LXS) with equivalent weights ranging from 345to 472 with well-defined molecular structures.
We used information about a previously described quantitative relationshipbetween the mole fractions of the individual surfactant components and theireffect on the optimal salinity in surfactant/ crude-oil/brine systems. Thisrelationship makes it possible to calculate blend compositions that havenear-optimal properties with respect to the required salinity at which thethree phases-i.e., oil, microemulsion, and brine-occur. In this work, however,we have further refined the correlation between surfactant structure parametersand performance by including the effect of factors such as the mole-fractionperformance by including the effect of factors such as the mole-fractiondistribution, the aromatic substitution pattern of the alkylxylenesulfonates,and the presence of the cosurfactant Enordet 3ES.
We studied the performance aspects of optimal salinity, the solubilizationof crude oil and brine at the optimal salinity, and the sensitivity to divalentions expressed as the "effectiveness ratio."
The data generated in this study make it possible to adjust the propertiesof a surfactant blend in relation to the characteristics of a properties of asurfactant blend in relation to the characteristics of a crude-oil reservoir,thus minimizing the need for trial-and-error experiments.
To facilitate the selection of a proper surfactant blend for the micellarflooding of a watered-out crude-oil reservoir, we must understand therelationships that exist between typical reservoir parameters and theproperties of the surfacant. Apart from providing insight into the factorsproperties of the surfacant. Apart from providing insight into the factors thatgovern effective flooding procedures, these relationships make it possible toadjust the surfactant according to the characteristics of the possible toadjust the surfactant according to the characteristics of the reservoir and,thus, to minimize the need for trial-and-error experiments. The surfactantdesign sequence often consists of the following steps: phase behavior studieswith the salinity of the connate water, water/oil ratio (WOR), nature of thecrude oil, and temperature as the major experimental parameters, followed byoil recovery experiments from cores, usually with parameters, followed by oilrecovery experiments from cores, usually with an iterative approach. We willconfine the discussion to surfactant/brine/oil (SBO) phase behavior studiesunder reservoir conditions and the resulting performance characteristics, suchas optimal salinity, solubilization parameter (SP), and salinity window(SW).
The effect of salinity on the phase behavior of SBO systems has beeninvestigated most widely. Several quantitative relationships between optimalsalinity for minimum interfacial tensions (IFT's) and surfactant blendcomposition have been described. Empirical formulas for certain petroleumsulfonates as well as synthetic sulfonates and nonionics have petroleumsulfonates as well as synthetic sulfonates and nonionics have been published.The effects of the nature of the oil phase and of temperature on the SBO phasebehavior have also been discussed.
We reported the relationship between the optimal salinity (midpoint salinity[MPS]) as well as the SP and the mole fractions of the surfactant components.The surfactant components studied are linear alkyl-o-xylenesulfonates with arange of molecular weights depending on the length of the alkyl chain (Fig1).
The detailed aromatic isomer distribution is shown in Fig 2. These isomerswill be referred to as Enordet LXS followed by the average equivalent weight oras Cn -LXS with the index indicating the number of the carbon atoms of thealkyl chain. In addition, Enordet 3ES, an alkyl-ethoxysulfate based on along-chain alcohol condensed with three ethylene-oxide units, was used to boostthe salt tolerance of blends of Enordet LXS:
Cn H2n+1 (0 -CH2 -CH2) 30SO 3 Na
where n = 12 through 15 for Enordet 3ES. This component will be referred toas the cosurfactant. (We confine the term "cosurfactant" to truesurfactants and exclude low-molecular-weight alcohols, which are usually alsopresent in these blends. In the literature, the term "cosurfactant" isoften used for both surfactants and alcohols.)
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