HLB number, Oil & Gas Glossary

What Is the HLB Number?

The HLB (hydrophile-lipophile balance) number is a dimensionless scale from 0 to 20 that quantifies the relative affinity of a surfactant molecule for water versus oil, with low values (1-6) indicating oil-soluble, water-in-oil emulsifying surfactants and high values (12-20) indicating water-soluble, oil-in-water emulsifying surfactants, used in oilfield applications to select surfactants for emulsion breaking, drilling fluid emulsification, and enhanced oil recovery surfactant flood design.

Key Takeaways

HLB was developed by Griffin (1949) as a semi-empirical scale to predict surfactant emulsification behaviour.
HLB 3-6: water-in-oil emulsifiers; HLB 8-13: oil-in-water emulsifiers; HLB 13-15: detergents; HLB 15-18: solubilisers.
The HLB of a surfactant blend is the weighted average of the individual HLB values by weight fraction.
Required HLB of an oil phase (the HLB needed to stabilise its emulsion) is a fixed property of that specific crude oil or oil cut.
OBM emulsifiers are selected with HLB values of 3-6 to produce stable water-in-oil drilling fluid emulsions.

How the HLB Number Is Defined and Used

The HLB system was introduced by William C. Griffin of Atlas Chemical Industries in 1949 to systematise the selection of nonionic emulsifying surfactants. For ethoxylated nonionic surfactants, the HLB is calculated as HLB = (weight percent hydrophilic ethylene oxide group) / 5. For other surfactant types, empirical correlation methods or Davies' group contribution method (which sums hydrophilic and lipophilic group contributions from the molecular structure) provide HLB estimates. The scale runs from 0 (fully lipophilic, oil-soluble, water-insoluble) to 20 (fully hydrophilic, water-soluble, oil-insoluble). Most commercial surfactants fall between HLB 1 and HLB 20.

The practical application of HLB in emulsion formulation uses the concept of required HLB: each oil phase has a specific required HLB value at which it forms the most stable emulsion with a given water phase. Matching the surfactant (or surfactant blend) HLB to the required HLB of the oil phase minimises the interfacial tension at the oil-water interface and maximises emulsion stability. For oil-based drilling muds, the target is a stable water-in-oil emulsion with the aqueous phase (brine) dispersed as small droplets in the oil continuous phase; this requires surfactants with HLB 3-6. For demulsification (breaking crude oil emulsions at surface separators), surfactants with HLB values close to the required HLB of the crude oil but with properties that destabilise rather than reinforce the interfacial film are used.

HLB Number Applications Across International Jurisdictions

In Canada, HLB-based surfactant selection is used in OBM and SBM (synthetic-base mud) formulation for WCSB horizontal well drilling where stable water-in-oil emulsion is required for borehole stability in reactive shale sequences. Drilling fluid formulators specify the HLB of primary and secondary emulsifiers (such as lecithin, tall oil derivatives, or synthetic polyglycerol oleate esters) in the mud specification sheet submitted with the drilling programme to the AER. SAGD produced fluid demulsification chemistry uses HLB matching to select dehydration chemicals that break the tight steam-stabilised water-in-oil emulsions from Cold Lake and Athabasca operations.

In the United States, HLB-based surfactant screening is applied in Gulf of Mexico OBM programmes and in Permian Basin SBM formulations for horizontal completion wells. BSEE offshore discharge regulations for OBM cuttings and fluids mandate compliance with Low Toxicity Oil (LTO) and other environmental standards; the choice of emulsifier type and HLB affects both the emulsion stability and the environmental profile of the mud system. In Norway, OSPAR Convention restrictions on offshore discharge of synthetic and mineral oil-based drilling fluids have driven NCS operators to use OSPAR green-listed emulsifiers with low aquatic toxicity, and HLB values of these approved emulsifiers must achieve the required water-in-oil emulsion stability for SBM systems used in North Sea drilling. In the Middle East, Saudi Aramco's OBM formulations for Arab Formation horizontal wells use HLB-selected emulsifier blends that provide stability at the high bottomhole temperatures (120-160°C) encountered in deep Jurassic formations.

Fast Facts

The required HLB of a crude oil for a water-in-oil emulsion typically ranges from 3 to 7 for most crude oils, while the required HLB for oil-in-water emulsification typically ranges from 10 to 14. This gap in required HLB between the two emulsion types explains why OBM emulsifiers (HLB 3-6) are very different compounds from oil-in-water emulsifiers (HLB 10-14): they work by having their molecular affinity balanced in opposite directions relative to the interface. A surfactant with HLB exactly matching the required HLB of the system minimises interfacial tension to its absolute minimum — the physical basis for why optimal HLB matching produces the most stable emulsions and why mismatched HLB produces unstable, phase-separating systems.

HLB and Surfactant Flooding EOR

In surfactant flooding enhanced oil recovery, the HLB concept is related to but distinct from the Winsor phase behaviour framework. The HLB of a surfactant determines its water-oil partitioning, and the Winsor type (I, II, III, IV) of the resulting microemulsion system reflects the combined HLB of the surfactant, the salinity (which modifies the effective HLB through ion-surfactant head group interactions), and the temperature. For EOR surfactant design, the goal is to select a surfactant with an HLB that, at the reservoir temperature and formation water salinity, produces Winsor Type III behaviour with minimum interfacial tension. This means the effective HLB of the surfactant at reservoir conditions must be approximately at its "optimal" value — the value at which the surfactant is equally soluble in oil and water phases. Temperature and salinity scans of candidate surfactants are conducted to identify the HLB-salinity-temperature combination that achieves minimum IFT at the specific reservoir conditions.

Tip: When blending surfactants to achieve a target HLB value, remember that HLB blending is strictly additive by weight only for nonionic surfactants of similar molecular structure. Blending a high-HLB ionic surfactant with a low-HLB nonionic surfactant does not give an HLB intermediate between the two individual values in a predictable way; ionic surfactants do not follow the linear HLB addition rule that works for nonionic blends. For blends that include ionic and nonionic surfactants (common in EOR co-surfactant formulations), the effective HLB must be determined experimentally by emulsification testing rather than calculated from the linear average formula. Conduct bottle tests across a range of blend ratios to find the composition that provides the desired emulsification or phase behaviour, rather than relying on calculated HLB alone.

HLB number is also referenced as:

Hydrophile-lipophile balance — the spelled-out form; used in technical reports, journal publications, and regulatory submissions; "HLB" is the universally recognised abbreviation in chemistry and engineering contexts
Griffin HLB — the specific attribution to W.C. Griffin's original 1949 formulation; used to distinguish from the Davies HLB (which uses group contributions rather than ethylene oxide content) in discussions of multiple HLB calculation methods
Required HLB — not the HLB of the surfactant but the HLB needed by a specific oil phase to form a stable emulsion; the target value against which surfactant HLB is matched in formulation work

Frequently Asked Questions

How is the HLB of an unknown surfactant determined experimentally?

When the chemical structure of a surfactant is not available for calculation or the Griffin formula is not applicable, the required HLB is determined experimentally using the emulsification test. A series of surfactants with known HLB values spanning the range of 2-18 are each tested with the oil phase of interest at fixed concentration; the surfactant that produces the most stable emulsion (smallest droplet size, longest separation time, highest turbidity retention) has an HLB closest to the required HLB of that oil. This test identifies the required HLB directly from experimental observation rather than calculation. For a complex crude oil with multiple fractions, the required HLB may also be determined by blending two surfactants with known HLBs at different ratios and identifying the blend ratio at which the emulsion stability is maximised — the blend HLB at maximum stability is the required HLB.

Why does increasing water salinity shift the effective HLB of a surfactant?

For anionic surfactants such as petroleum sulfonates (common in EOR flooding), increasing salt concentration in the brine phase suppresses the electrostatic interactions between the negatively charged sulfonate head groups and the water molecules, reducing the hydrophilicity of the surfactant and lowering its effective HLB. This shift in effective HLB as a function of salinity is the physical basis for the Winsor phase type transitions with salinity described in the surfactant EOR literature: low salinity → Type I (high effective HLB, oil-in-water dominant), optimal salinity → Type III (balanced HLB, minimum IFT), high salinity → Type II (low effective HLB, water-in-oil dominant). Understanding this salinity-HLB relationship allows EOR formulators to design surfactant systems that achieve the optimal HLB at the specific formation water salinity of the target reservoir.

Why the HLB Number Matters in Oil and Gas

The HLB number is the foundational framework for surfactant selection across the full range of oil and gas applications: emulsifier selection for oil-based and synthetic-base drilling muds that must maintain stable water-in-oil emulsions at downhole temperatures and pressures; demulsifier selection for produced fluid separation where stable crude oil emulsions must be broken before export; and EOR surfactant design where the HLB (expressed through the Winsor framework) determines whether the surfactant achieves the ultralow interfacial tension needed for residual oil mobilisation. Incorrect HLB selection in any of these applications has direct operational consequences — an unstable OBM emulsion compromises wellbore stability, an ineffective demulsifier raises BS&W above pipeline specification, and an off-optimal HLB EOR surfactant fails to achieve minimum IFT and wastes the cost of the chemical slug. The HLB framework, despite its age (1949) and simplifications, remains the most practical single-number guide to surfactant phase behaviour in oilfield applications.

HLB Number: Definition, Surfactant Selection, and Enhanced Oil Recovery Applications