Contents

Oil & Gas Industry
The Practical Guide to Surface Science (2026)

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Written by
Dr Amit Pratap Singh
PhD, Delhi University Post Doc - AIST Japan
Guest Author
Read More
alidad
Reviewed by
Dr Alidad Amirfazli
Dr. Amirfazli, a leading expert in surface wetting and superhydrophobic coatings, has 250+ publications, edits Advances in Colloid and Interface Science, and has received multiple research awards.
Scientific Advisor & Co-founder
Read More
D54c15105cfe94f786c500e4091d6ea65457608fde49ba183c8f862814a54249?s=100&d=m
Written By

Dr Amit Pratap Singh

Guest Author

PhD, Delhi University

Post Doc - AIST Japan

alidad
Reviewed By

Dr Alidad Amirfazli

Scientific Advisor & Co-founder

Dr. Amirfazli, a leading expert in surface wetting and superhydrophobic coatings, has 250+ publications, edits Advances in Colloid and Interface Science, and has received multiple research awards.

Featured Studies & Publications

Research Paper Contact angle measurement with a smartphone
Research Paper Surface tension measurement with a smartphone using a pendant drop

This is a practical guide to Surface Science for researchers working in the Oil & Gas Industry.

In this all-new guide you’ll learn all about:

  • Crucial surface science principles
  • The significance of surface science measurements for the Oil & Gas industry
  • Applicable ASTM Standards & Guidelines

Let’s dive right in.

Oil & Gas

Contents

measurement

Contact Angle Measurement

tension

Surface Tension Measurement

energy

Surface Energy Measurement

sliding angle

Sliding Angle Measurement

realworld

Real World Applications

standardand guide

Standards and Guidelines

Executive Summary

What it covers: How oil and gas labs use interfacial tension, surface tension and contact angle to screen surfactants, polymers and brines. Each measurement is tied to a field problem, a standard and published client work.
Key insights: Contact angle on aged mineral plates under brine ranks surfactants by how far they shift a surface toward water wet. Polymer and surfactant mixtures can behave unlike either one alone, and one published study found surface tension fell to a minimum and then rose again. Pendant drop works down to about 1 mN/m, so ultralow interfacial tension needs another method.
Business value: Ranking chemicals on the bench means fewer weak candidates reach slow and costly core floods. One portable kit measures interfacial tension, surface tension and contact angle, so a service or field lab can screen without sending samples out.
Standards to follow: API RP 13B covers field tests of water based and oil based drilling fluids, and it has no surface tension or wettability test. ASTM G205 includes a contact angle check of oil and brine on steel, and API RP 40 covers core analysis. Use the edition your contract or quality system names.
Bottom line: Use interfacial tension and contact angle to shortlist chemicals, then confirm the best candidates on cores and in the RP 13B tests. Book a 15 minute demo to try it on your own fluids.

Chapter 1: Introduction

In oil and gas work, many costly results start at an interface. A surfactant that does not lower oil and water interfacial tension enough leaves oil behind in the rock. A drilling fluid additive that changes wetting can affect the whole mud system.

These are the places where wetting decides yield in oil and gas:

The Dropometer drop shape analysis kit measures contact angle, surface and interfacial tension, surface free energy and sliding angle with one portable setup. Its method was validated against a KRUSS DSA100E in two peer reviewed papers. If you are new to the terms, start with wettability.

We use the following surface properties to understand the behavior of Oil & Gas products and improve their quality.

Chapter 2: Contact Angle Measurement

The contact angle quantifies the wettability of a surface by representing the angle between a liquid’s surface and a solid surface.
Dropletlab Research

Sample Image taken from Droplet Lab Tensiometer.

Young – Laplace Method

  • 1. This method uses the whole drop profile to calculate the contact angle value.
  • 2. This method is only compatible with an axisymmetric drop, which is not always seen in practice because a needle is typically inserted into the drop to increase or decrease the drop volume.
  • 3. This method yields more consistent results than the polynomial fitting method.

Polynomial Method

  • 1. This method uses only a portion of the drop profile to calculate the contact angle value.
  • 2. This method is compatible with both axisymmetric and non-axisymmetric drops.
  • 3. The measurement results of this method are less consistent, as they can be influenced by local surface imperfections.
Dynamic Contact Angle

Ideally, when we place a drop on a solid surface, a unique angle exists between the liquid and the solid surface. We can calculate the value of this ideal contact angle (the so-called Young’s contact angle) using Young’s equation. In practice, due to surface geometry, roughness, heterogeneity, contamination, and deformation, the contact angle value on a surface is not necessarily a single consistent value but rather falls within a range. The upper and lower limits of this range are known as the advancing and receding contact angles, respectively. The values of advancing and receding contact angles for a solid surface are highly sensitive to many parameters, such as temperature, humidity, homogeneity, and minor contamination of the surface and liquid. For example, the advancing and receding contact angles of a surface can differ at different locations.

Dynamic Contact Angle versus Static Contact Angle

Practical surfaces and coatings naturally show contact angle hysteresis, indicating a range of equilibrium values. When we measure static contact angles, we get a single value within this range. Solely relying on static measurements poses problems, like poor repeatability and incomplete surface assessment regarding adhesion, cleanliness, roughness, and homogeneity.

In practical applications, we need to understand how easily a liquid spreads (advancing angle) and how easily it is removed (receding angle), such as in painting and cleaning. Measuring advancing and receding angles offers a holistic view of liquid-solid interaction, unlike static measurements, which yield an arbitrary value within the range.

This insight is crucial for real-world surfaces with variations, roughness, and dynamics, aiding industries like cosmetics, materials science, and biotechnology in designing effective surfaces and optimizing processes.

Learn how Contact Angle measurement is done on our Tensiometer

For a more complete understanding of Contact Angle measurement, read our Contact Angle measurement: The Definitive Guide

Contact Angle measurement: The Definitive Guide

Open Benchmark Data: Contact Angle & Surface Energy

These reference measurements show how deionized water wets four standard substrates measured with the Droplet Lab Dropometer. Use them as visual and numerical benchmarks when you're checking your own sample preparation, treatments, and chemistry.

Full contact angle and surface energy datasets (including additional liquids and statistics) are available on our dataset hub.

Glass - DI Water
Glass - DI Water
Nylon - DI Water
Nylon - DI Water
PMMA - DI Water
PMMA - DI Water
Teflon - DI Water
Teflon - DI Water

The droplet images above are taken from the same benchmark series as our open dataset. For each substrate and probe liquid we report:

● Advancing and receding contact angles (and hysteresis)
● Derived surface energy (SFE) values based on multi-liquid measurements
● Measurement conditions, uncertainties, and sample preparation details

Comparing your own droplet shapes and angles against these references is a fast way to spot contamination, treatment drift, or unexpected changes in wettability.

Explore the full benchmark datasets (contact angle + surface energy)

Measurements were performed with the Droplet Lab Dropometer under controlled laboratory conditions. Treat these values as sanity checks and starting points for your own process targets, not as product specifications.

Chapter 3: Surface Tension Measurement

This property measures the force that acts on the surface of a liquid, aiming to minimize its surface area.

Surface Tension Measurement

Sample Image taken from Droplet Lab Tensiometer

Dynamic Surface Tension

Dynamic surface tension differs from static surface tension, which refers to the surface energy per unit area (or force acting per unit length along the edge of a liquid surface).

Static surface tension characterizes the equilibrium state of the liquid interface, while dynamic surface tension accounts for the kinetics of changes at the interface. These changes could involve the presence of surfactants, additives, or variations in temperature, pressure, and composition at the interface.

When to use Dynamic Surface Tension Measurement

Dynamic surface tension is essential for processes that involve rapid changes at the liquid-gas or liquid-liquid interface, such as droplet and bubble formation, coalescence (change in surface area), the behavior of foams, and the drying of paints (change in composition, e.g., evaporation of solvent). It is measured by analyzing the shape of a hanging droplet over time.

Dynamic surface tension applies to various industries, including cosmetics, coatings, pharmaceuticals, paint, food and beverage, and industrial processes, where understanding and controlling the behavior of liquid interfaces is essential for product quality and process efficiency.

Learn how Surface Tension measurement is done on our Tensiometer

For a more complete understanding of Surface Energy measurement, read our Surface Tension measurement: The Definitive Guide

Surface Tension measurement: The Definitive Guide

Chapter 4: Surface Energy Measurement

Surface energy refers to the energy required to create a unit area of a new surface.
231

Sample Image taken from Droplet Lab Tensiometer

Learn how Surface Energy measurement is done on our Tensiometer

For a more complete understanding of Surface Energy measurement, read our Surface Energy measurement: The Definitive Guide

Surface Energy measurement: The Definitive Guide

For benchmark contact angle and surface energy values on glass, nylon, PMMA, and Teflon, see the Open Benchmark Data panel above or visit our Dataset Hub for full CSV downloads.

Dataset Hub

Chapter 5: Sliding Angle Measurement

The sliding angle measures the angle at which a liquid film slides over a solid surface. It is commonly employed to assess the slip resistance of a surface.

sliding angle 1

Sample Image taken from Droplet Lab Tensiometer

Learn how Sliding Angle measurement is done on our Tensiometer

For a more complete understanding of Sliding Angle measurement, read our Sliding Angle Measurement: The Definitive Guide

Sliding Angle Measurement: The Definitive Guide

Chapter 6: Real-World Applications

Within the Oil & Gas industry, several case studies exemplify the advantages of conducting surface property measurements.

Steady Shear Rheology and Surface Activity of Polymer-Surfactant Mixtures

The study evaluates how five surfactants (anionic, cationic, zwitterionic, and non-ionic) change the steady-shear rheology and surface activity of two polymers (cationic HEC-based LR-400 and anionic PAM-based Praestol 2540TR). Solutions show shear-thinning power-law behavior. Anionic surfactants strongly increase the consistency index and shear-thinning in the cationic polymer system, while effects on the anionic polymer are weak/modest. Surface tension decreases with surfactant concentration, and Amphosol CG is most effective at lowering surface tension and increasing conductivity. Approximate CAC and PSP are estimated from slope changes in surface-tension-concentration plots.

Role of the Droplet Lab Goniometer

  • The Droplet Lab instrument was used specifically for surface tension measurement (not contact angle) via a smartphone-based tensiometer using ADSA (Axisymmetric Drop Shape Analysis) on pendant droplets. The Droplet Lab measurement enables quantifying how surfactant type and concentration shift interfacial properties of polymer-surfactant fluids, critical for designing oilfield fluids where interfacial behavior influences wetting/cleanup and formulation performance.
  • Where it’s mentioned in the paper: Surface tension method and Droplet Lab instrument are described in Section 2.4 “Surface Tension Measurements” (page 5), including the ADSA pendant-drop workflow and repeat measurements.

Key Findings

  • Polymer-surfactant solutions behaved as shear-thinning fluids and were fit with the power-law model (rheology context for fluid design).
  • Anionic surfactants (Stepanol WA-100, Stepwet DF-95) produced strong rheology changes in the cationic polymer (LR-400) system, increasing consistency and making the fluids more shear-thinning (useful for tuning pumpability vs. carrying capacity).
  • For anionic polymer (Praestol 2540TR), surfactants showed weak to modest effects overall on rheology (more formulation robustness to surfactant choice).
  • Surface tension decreases as surfactant concentration increases across systems (interfacial control via surfactant dosing).
  • Amphosol CG (zwitterionic) was the most effective at reducing surface tension at a given ppm concentration and produced the largest conductivity increase.
  • Approximate CAC and PSP points were inferred from slope changes in surface tension vs. concentration plots (useful for identifying “binding/saturation” regimes).

Why It Matters

For oilfield fluid formulation (hydraulic fracturing, drilling, and related EOR-adjacent workflows), the ability to quantify surface tension vs. surfactant concentration alongside rheology changes helps teams select polymer-surfactant pairs that hit performance targets (e.g., low-shear viscosity for suspension, manageable high-shear viscosity for pumping, and controlled interfacial behavior). The Droplet Lab surface tension measurements provide a practical way to set spec windows and avoid over- or under-dosing surfactants relative to interaction regimes (CAC/PSP).

Method Snapshot

  • Samples: Aqueous polymer solutions of LR-400 (cationic HEC-based) and Praestol 2540TR (anionic PAM-based) with added surfactants (Stepanol WA-100, Stepwet DF-95, HTAB, Amphosol CG, Alfonic 1412-3).
  • Droplet Lab measurement: Pendant droplet surface tension at ~22 °C using smartphone imaging + ADSA; 12 repeats per solution averaged (surface tension reported in mN/m). (No contact angle / advancing-receding angles were measured in this study.)

Data Note

Comparisons of Surface tension of different surfactants in LR-400 polymer solution.

Figure

Citation (APA Format)

Lu, Q., &; Pal, R. (2025). Steady Shear Rheology and Surface Activity of Polymer-Surfactant Mixtures. Polymers, 17(3), 364

View Publication →

Water and oil separation

Produced fluids separate faster when the film between oil and water drops breaks easily. Interfacial tension between the oil and water phases is a fast first screen for demulsifiers and surfactants, before longer bottle tests.

The pendant drop method forms a drop of one liquid inside the other and reads the tension from its shape. Researchers at Yale, Emory and the City College of New York measured oil and water interfacial tension on the Dropometer. They used it in a study of oil droplets flowing and clogging in narrow gaps.

Water and oil separation

Polymer flooding fluids

Polymer floods often carry surfactants, and the two can interact in solution. Surface tension across a surfactant dose series, measured alongside rheology, shows where the mixture changes behaviour.

Researchers measured pendant drop surface tension on the Dropometer in three such studies. They covered polymer and surfactant mixtures, a cationic polymer with an anionic surfactant and four polymers with added surfactants. The papers name enhanced oil recovery and drilling as uses. All three tested at room temperature, so repeat the screen at your own conditions.

Polymer flooding fluids

Offshore pipeline protection

Whether oil or brine wets the steel affects corrosion inside a pipeline. The contact angle of an oil drop held under a steel coupon in brine shows which phase the surface prefers.

ASTM G205 includes this kind of wettability check among its tests of crude oil corrosivity. The Dropometer covers the contact angle part with the optional cuvette, while the emulsion and corrosion parts need other equipment. Coating teams can also use contact angle measurement to check steel before coating.

Offshore pipeline protection

Exploration and production

Drilling fluids and cores are tested to set procedures, and wetting checks fit around those tests. API RP 13B covers field tests of water based and oil based muds, such as density, rheology and filtration. It has no surface tension or wettability test, so the Dropometer sits before or after it.

Measure surface tension when you qualify a mud additive, and check wetting when you look for the cause of a poor result. API RP 40 covers core analysis, and our page explains where a wettability check fits. See also surfactant screening for drilling and fracturing fluids.

Exploration and production

Enhanced oil recovery chemicals

EOR labs often have more surfactant, nanofluid and brine candidates than core tests can cover. A bench screen ranks them by interfacial tension and by how far each moves an oil wet surface toward water wet.

Our wettability alteration use case sets out the test on aged mineral plates under brine. Pendant drop works down to about 1 mN/m, so ultralow interfacial tension needs another method. Bench temperature is not reservoir temperature, so confirm shortlisted chemicals on cores before field use.

Enhanced oil recovery chemicals

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If you are interested in implementing these or any other applications, please contact us.

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Chapter 7: Standards and Guidelines

In an industry where precision reigns supreme, how can Oil & Gas manufacturers ensure their products withstand scrutiny? The answer lies in standards and guidelines: the compass that guides them through the complex maze of quality and performance.

API RP 13B-2, Field Testing Oil-Based/Synthetic-Based Drilling Fluids (incl. Electrical Stability)

What it is

API RP 13B-2 is a recommended practice that defines field test procedures for oil-based and synthetic-based (invert-emulsion) drilling fluids, including the Electrical Stability (ES) test. Dropometer fits as a diagnostic companion by adding oil-brine interfacial tension (IFT) and solids/coupon wettability measurements to help explain why an ES trend is changing.

When to use it

Routine OBM/SBM QA/QC trending

Run RP 13B-2 field tests (especially ES) as your operational “early warning,” and add IFT/wettability when you need mechanism behind drift.

Troubleshooting after an upset or treatment change

When ES shifts after dilution, contamination, solids changes, or chemical additions, use IFT + wettability to narrow whether the issue is primarily interfacial chemistry vs solids wetting.

In-scope / Out-of-scope

In scope
  • RP 13B-2 field testing for OBM/SBM, including Electrical Stability (ES) as a trended condition indicator
  • Mechanistic augmentation (not replacement): oil-brine IFT via pendant-drop (controlled temperature/composition)
  • Wettability verification: contact-angle-based indicator (site-defined geometry) on representative substrates (steel/shale/cuttings analogs)
  • Trend correlation: ES (field) plotted alongside IFT and wettability indicators to support hypothesis-driven treatment decisions
Out of scope
  • Replacing RP 13B-2 or claiming API compliance/certification via Dropometer results (it’s an augmentation tool, not a standard)
  • Single-cause diagnosis from ES alone (ES is multi-factor and should not be treated as a one-to-one “root cause” meter)
  • Full additive R&D programs unless explicitly scoped (e.g., broad surfactant screening beyond a targeted optimization study)
  • Optically invalid measurements without documented controls/acceptance criteria (e.g., non-axisymmetric drops, poor edge detection, uncontrolled temperature/density inputs)

Minimum you must report (checklist)

  • Electrical Stability (ES) result(s) being trended (value + date/time + instrument/procedure reference)
  • Sample metadata: mud system (OBM/SBM), well/section, sampling method, temperature, time since last treatment/dilution, notable contamination/solids observations
  • Oil & brine identities/composition used for IFT (source, salinity/chemistry, and whether phases were extracted or prepared)
  • IFT result (mN/m) with method (pendant drop), test temperature, densities used for fitting, and replicate count + summary statistic (mean ± SD or median + spread)
  • Wettability indicator (contact angle metric) with substrate/coupon type, surface prep/conditioning, geometry/environment, replicate/spot count + summary statistic
  • Trend plots: ES vs time; IFT vs time; wettability indicator vs time (and ES vs IFT if you’re correlating)
  • Controls: reference oil-brine pair and/or “golden” OBM sample frequency + results; reference coupon with known response
  • Data-quality outcomes: acceptance limits and any rejected/re-run points (e.g., drop symmetry, fit residual thresholds, temperature/density tolerances)

ES is best treated as a high-sensitivity trend indicator, not a stand-alone explanation of what failed. IFT and wettability thresholds must be site-calibrated against your own KPIs (rheology/sag/filtration/torque-drag/NPT signals) before being used as action limits.

How to interpret results (guardrails)

  • Use ES as the trigger, not the diagnosis: ES drift tells you “something changed,” while IFT/wettability help narrow what kind of change is most likely.
  • IFT rising with little wettability change → consistent with weakening interfacial-active chemistry (emulsifier effectiveness/brine chemistry/contamination hypotheses); prioritize brine verification, emulsifier strategy, contamination checks.
  • Wettability shifting toward water-wet with normal IFT → consistent with solids wetting program slipping (wetting agent depletion/solids conditioning/solids loading); prioritize solids control and wetting-agent strategy review.
  • ES noisy + IFT/wettability variable → likely multi-factor change and/or sampling heterogeneity; standardize sampling/conditioning, repeat with controls, and avoid chemistry-altering “over-filtration.”
Read our API RP 13B-2 page

Now It’s Your Turn

We hope this guide showed you how to apply surface science in the Oil & Gas industry.

Now we’d like to turn it over to you: 

  • What’s the #1 real-world application from this post that you want to try first?
  • Perhaps we missed a relevant industry standard.
  • Or maybe you have a question about something you read.

Feel free to leave a comment below—we’d love to hear from you.

Frequently asked questions

Which surface measurement should an oil and gas lab start with?

Start with the decision you need to make. Use interfacial tension to rank surfactants against oil, and surface tension to set surfactant dose in drilling and fracturing fluids. Use contact angle under brine to see whether a chemical moves rock or steel toward water wet. Our surface tension and contact angle guides explain each method.

Which standards apply to wettability and interfacial tension in oil and gas?

ASTM G205 includes a contact angle check of oil and brine on steel as part of judging crude oil corrosivity. API RP 13B covers drilling fluid field tests and has no surface tension or wettability test. API RP 40 covers core analysis. The Dropometer uses the pendant drop and sessile drop methods, so check which method your specification names.

Can the Dropometer measure ultralow interfacial tension?

Not below about 1 mN/m. The pendant drop method needs a hanging drop with a clear, measurable shape, and that sets its floor. Ultralow interfacial tension, as in some surfactant floods, needs a spinning drop instrument. Above that floor, the Dropometer is useful for ranking candidates quickly. See interfacial tension for the basics.

How do I measure contact angle on rock or steel under brine?

Hold a polished, aged mineral plate or steel coupon in brine inside the optional cuvette. Release an oil drop under the plate and measure the angle through the water phase. Compare each chemical against an untreated plate. This is a bench screen, not a core test, so it does not give core scale wettability indices. See the captive bubble method for the geometry.

How does a polymer change the surface tension of a surfactant solution?

It depends on the pair. In one published study, a cationic hydroxyethyl cellulose solution reached its lowest surface tension at a middle surfactant dose, then rose again at higher doses. Other polymer and surfactant pairs showed weak interaction and a smooth fall. Measure your own pair across a dose series. See this study of a cationic polymer and anionic surfactant.

Can one lab bench cover contact angle, surface tension, surface energy and sliding angle?

Yes. A lubricant base oil maker set up all four measurements on one Dropometer bench, and one person assembled and set it up. It ordered the kit as two itemised purchases to fit its research contract. Tell us which fluids and surfaces you test, and we will suggest a configuration.

How accurate is the Dropometer?

The drop shape method was validated against a KRUSS DSA100E in two peer reviewed papers, one in Review of Scientific Instruments and one in Colloids and Surfaces A. Published contact angle accuracy is 0.35 degrees. Automatic edge and baseline detection gives the same reading from the same image. See our validation papers.

Standards, evidence and resources

1. Industry standards
  • API RP 13B: drilling fluid field testing: Covers field tests of water based and oil based muds with no surface tension or wettability test, so Dropometer checks on additives and filtrates sit before or after it.
  • API RP 40: core analysis and wettability: Covers coring, core handling and saturation, porosity and permeability, and asks that wettability be measured soon after recovery, which an oil and brine contact angle can support.
  • ASTM G205: crude oil corrosivity and steel wetting: Guides judging crude oil corrosivity through emulsion behaviour, steel wettability and water phase corrosivity; an oil drop held under a steel coupon in brine gives the wettability contact angle.
Use cases
  • Foam control and foam quality tuning: Pendant drop surface and interfacial tensions give entry, spreading and bridging coefficients for picking defoamers, and show how surfactant level and adsorption speed shape foam in oilfield fluids.
  • Drilling and fracturing fluid surfactant screening: Surface tension and interfacial tension across surfactant dose and salinity help shortlist flowback aids and mud additives before core tests, within the pendant drop floor near 1 mN/m.
  • Wettability alteration screening for EOR chemicals: Oil drop contact angle under brine on aged mineral plates ranks how far each surfactant or chemical moves a surface toward water wet, before slower core floods.
Case studies Client citations (our analysis of each paper)
  • Cationic polymer and anionic surfactant mixtures: Pendant drop surface tension of a cationic cellulose polymer with sodium lauryl sulfate fell from 64.09 to 27.06 mN/m at 250 ppm, then rose, relevant to EOR and fracturing fluids.
  • Flow and clogging of capillary droplets: Octane and water interfacial tension of about 10 mJ/m² set the capillarity reference for droplets squeezing through narrow orifices and obstacle arrays, where clogging depends on droplet stiffness.
  • Added surfactants in polymer solutions: Pendant drop surface tension of four polymers, including guar and xanthan gum, dosed with four surfactant types showed which pairs interact, a check for EOR, fracturing and drilling fluids.
  • Shear rheology and surface activity of polymer surfactant mixtures: Pendant drop surface tension of two polymers with five surfactants gave approximate aggregation and saturation points, a guide to surfactant dosing in polymer based EOR and drilling fluids.
Use case collections Further resources