Willow Liu, SPE, is a chief scientist leading research and product innovation in advanced multiphase flow measurement, including at MEDENG. With more than 25 years of experience, she specializes in complex non-Newtonian multiphase flows across biomedical and oil and gas applications. Her recent work focuses on emissions quantification and management using advanced engineering tools.
An active SPE leader, she serves across multiple technical sections and contributes to webinars, standards discussions, and technical initiatives. Liu will serve on the 2026 ATCE Energy Transition Subcommittee and received the 2024 SPE Canada Regional Projects, Facilities, and Construction Award.
She holds an MS in engineering science and mechanics (biofluid mechanics) from Georgia Tech.
RS: Willow, thank you for taking the time to speak with us. Your career spans biomedical engineering, multiphase flow measurement in oil and gas, and now emissions quantification—a fascinating trajectory. To begin, could you tell us about your early career and how it shaped your technical foundation?
WL: Absolutely. I began biomedical engineering, modeling multiphase blood flow through complex arterial networks. It was a demanding environment shaped by tightly coupled physics: non-Newtonian fluid behavior, transient flow dynamics, limited sensing, and the elasticity of interconnected vessels. A key part of the work was inferring internal states that could not be measured directly. That blend of physical modeling, measurement constraints, and data-driven inference became foundational to how I approach engineering problems today.
RS: Many engineers remain within one discipline, but you transitioned from biomedical systems to the oil and gas sector. What inspired that move?
WL: For me, it was not a complete shift so much as a translation of the same physics into a different domain. Multiphase blood flow and multiphase oil and gas production share the same core challenge: different phases interacting under dynamic conditions, with only partial observability.
In hemodynamics, I worked with pulsatile flow, evolving phase interfaces, and sparse measurements. In oil and gas, the scale and operating envelope changed dramatically: long pipelines, higher pressures, harsher environments, and gas-liquid or oil-water mixtures with changing flow regimes. But the intellectual problem remained familiar. You still need mechanistic models, sensor fusion, and inference methods to estimate what cannot be measured directly.
What drew me to the transition was that continuity. The industrial setting amplified the complexity, but the underlying multiphase transport physics and the need for robust, model-informed measurement systems aligned directly with my background.
RS: You’ve now spent over 2 decades working in multiphase flow measurement. What were the realities of that work?
WL: Multiphase metering is one of those fields where physics keeps you humble. Flow regimes change, composition shifts, operating conditions move, and the measurement system must perform in real field environments, not ideal laboratory settings.
When I entered the field, multiphase flow metering was still a niche specialty and often seen as a black box. In many cases, radioactive-based measurements were regarded as the only dependable way to differentiate phases under complex flow conditions. The challenge then was often simply proving that a meter could work.
Over the past 2 decades, the field has changed significantly. The question is no longer just “Can we measure this?” but “Can we measure it better, and well enough to support operational decisions?” What was once dominated by a small number of hardware-intensive systems has expanded into a broader ecosystem of non-radioactive technologies, each suited to different fluids and operating conditions.
What excites me most is the rise of virtual multiphase flow meters. These approaches use artificial intelligence, machine learning, and physics-informed models together with basic field sensor signals, such as pressure and temperature, to model, predict, and verify multiphase flow behavior. I have had the opportunity to work closely on developing and applying these approaches, which represent a real shift in how we think about measurement.
At the same time, the fundamentals have not changed. A useful multiphase measurement system is not just an instrument; it is an engineering discipline that combines physics, metrology, software, diagnostics, and field experience. You need to know when a number is trustworthy, what assumptions sit behind it, and how it should be used.
After 2 decades, the challenge is still balancing rigor with practicality. As the industry integrates physics, data, and digital technologies more deeply, that discipline remains essential for turning complex measurements into decisions operators can trust.
RS: Today, your work focuses heavily on emissions, particularly methane. How do your earlier experiences influence this new focus?
WL: Very directly. Methane emissions may sound like a new domain, but technically it is the same class of problem: detecting, quantifying, and attributing a flow in a messy system with variable composition, intermittent behavior, changing boundary conditions, and limited sensor access.
My multiphase background influences how I think about emissions in three ways. First, I am cautious about single-phase assumptions. Many emission events involve wet gas, flashing liquids, aerosol carryover, or transient operations such as blowdowns and startups. If the physics is oversimplified, you do not just get a slightly wrong number; you can get the wrong trend and the wrong diagnosis.
Second, I bring a metrology mindset. You must define the measurand, close the mass balance where possible, and quantify uncertainty. Emissions reporting is still evolving, and results are often difficult to reconcile because volumetric rates, concentration enhancements, emission factors, and model-derived fluxes are mixed without a consistent mass-flow basis.
Third, inference under constraints is the common thread. In the field, you never get perfect instrumentation. Emissions quantification, like multiphase metering, is usually a fusion problem: physics models, multiple measurements, and operating context must work together, with uncertainty carried through the chain.
RS: You have mentioned that engineering fundamentals remain deeply relevant even as the energy system evolves. Could you elaborate?
WL: Absolutely. The energy transition does not reduce the need for engineering fundamentals; it raises the standard for applying them. In emissions work, the challenge is not only detecting a plume but translating what is observed into a decision-grade quantity that can support mitigation, reporting, and accountability.
A lot of current quantification approaches implicitly assume simpler physics than the field gives us. Many methods treat the source as steady, dry gas flow, even though real operations may involve phase change, entrained droplets, wet gas behavior, or rapid transients. That is one reason two teams can measure the same site on the same day and produce materially different results.
The other gap is reporting consistency. If the goal is credible accountability, we need a disciplined pathway to mass flow (kg/h methane, for example), with clear assumptions on composition, density, system boundaries, and uncertainty. Without that, it becomes difficult to compare methods, prioritize fixes, or demonstrate abatement outcomes with confidence.
This is where oil and gas has something valuable to contribute. The industry has decades of experience in metrology, uncertainty management, and measuring difficult fluids in harsh, dynamic conditions. Bringing that discipline into emissions measurement is how we move from broad estimates to results that operators, regulators, and investors can trust.
RS: Looking back, what stands out to you about your career path across disciplines?
WL: What stands out most is the continuity. On the surface, moving from blood-flow modeling to multiphase metering to methane emissions can look like a series of pivots. But the core problem has been remarkably consistent: using physics-based measurement and inference to make complex systems observable, quantifiable, and actionable.
And I will say this with pride: the measurement culture in oil and gas has deeply shaped how I work. It instilled respect for rigor, metrology discipline, and the responsibility that comes with a number, because in the field, measurements drive real decisions with real consequences.
That is the throughline in my career. Expertise evolves not by abandoning fundamentals, but by adapting them and taking proven measurement practices, modeling rigor, and field pragmatism into new contexts where credibility matters.
RS: Beyond your technical work, you’ve invested heavily in SPE as a volunteer and community builder. What motivated you to step into those roles, and how has volunteering with SPE benefited you professionally and personally?
WL: SPE is an esteemed professional organization, and I am proud and grateful to be part of it. For me, if I am involved, I want to be useful. I saw real opportunities within multiple SPE technical sections where I could contribute in a meaningful way, so I stepped up.
The experience has been tremendously rewarding. I have met talented, experienced, and generous engineers, and I have learned a great deal about this ever-evolving industry through the projects I have been part of.
I encourage every SPE member to try volunteering. If you believe you can help, if you have ever felt something could be done better, or if you want to become more visible and recognized, volunteer for SPE and be part of making those changes.
RS: Last question, outside of modeling complex fluids, what’s your favorite activity?
WL: Cooking. From a perfectly crusted French baguette—it took me 10 years to master—to the pursuit of umami in Chinese cooking, it is all about chemistry. And let’s not forget French sauces: beautifully emulsified multiphase fluids under a wide range of conditions.
RS: Willow, this has been a remarkably insightful conversation. Your career highlights how engineering fundamentals transcend industries and how oil and gas expertise can meaningfully support the energy transition. Thank you for sharing your journey with us.
WL: Thank you. I’m excited to contribute to this evolving landscape, and I’m glad to share my story.
