EOR/IOR terminology – time for a (real) change?

On August 1, 2024, the SPE community issued a call for public input on proposed changes to IOR/EOR terminology. Surveys showed limited understanding of these terms, prompting the need for clarity. However, upon reviewing the new proposals, including the introduction of an additional term (AOR), some found the changes even more confusing. The question arises: why not completely overhaul the terminology to simplify things instead of adding more complexity?

Words hold immense power in shaping how people think, perceive the world, and ultimately, how they act. The language we use not only reflects our thoughts but also influences them, creating frameworks within which we interpret our experiences and make decisions. This performative aspect of language means that the words we choose can actively shape realities, guiding collective attitudes, behaviors, and even the direction of entire industries.

An example lies with the well-established “Primary, Secondary, and Tertiary Oil Recovery” approach is deeply ingrained in the oil industry, and it is a foundational concept in all reservoir and petroleum engineering handbooks. This wording and methodology have undoubtedly guided the development of oilfields since the industry’s inception. While the rationale behind this approach is not necessarily in dispute, it is worth questioning the outcomes it has produced:

A few years ago, the IEA reported that the average recovery factor for oil-bearing formations was around 30%, leaving 70% of the oil untapped in the ground (source: IEA). In the scientific and engineering communities, a 30% yield should prompt a critical evaluation of the methods and strategies used in oilfield development. Despite nearly a century of experience and significant technological advancements, this low recovery rate remains the norm for most oilfields. Why continue to rely on approaches that have consistently proven to be insufficient? Why not include all techniques available to improve recovery?

Similar reports indicate that secondary processes yield between 5 and 14 barrels of water per barrel of oil produced. This energy- and CO2-intensive process should lead engineers to reconsider why so much emphasis is placed on waterflooding alone, without the immediate support of additional enabling techniques.

All reservoirs, whether sandstone or carbonate, share a critical characteristic: they are inherently heterogeneous. This means that any injected fluid will naturally follow the paths of least resistance unless specific measures (such as conformance treatments, viscous polymer floods, foams, or Water-Alternating-Gas (WAG) injections) are taken to promote a more uniform sweep of the reservoir. Consequently, conformance issues are inevitable, often emerging sooner rather than later. Once water fingering occurs, it becomes exceedingly difficult to resolve, largely due to the same challenges in reservoir characterization that prevented early detection. Ignoring these potential problems, despite knowing they will arise, overlooks the fact that we sample less than a fraction of the reservoir and will never fully understand it—except to know that it is heterogeneous, and challenges are certain to follow.

Having terms like AOR, EOR, IOR just makes things even more complicated. To simplify terminology and encourage a more scientifically grounded approach, it is important to revisit the established terms used in production/reservoir engineering. Drawing from the extensive knowledge, field cases, and research available through the SPE, we suggest the following changes:

• • Eliminate the terms “primary,” “secondary,” and “tertiary” recovery: These outdated terms and their sequential definitions fail to reflect the depth of experience and knowledge gained over the years. They often lead engineers to repeat practices that should no longer be considered best practice.
  • Introduce two main categories with relevant subdivisions: This updated framework better reflects contemporary scientific insights and encourages the adoption of more effective, evidence-based strategies in oilfield development. By doing so, we also avoid relying on the “baseline” concept, which reinforces the outdated notion of staged production—an approach that, as discussed, has significant limitations. Furthermore, there is growing evidence that companies initiating Enhanced Oil Recovery (EOR) immediately after so-called Primary production are achieving outstanding results, often surpassing those of traditional waterflooding. A prime example of this is Hilcorp’s success at Milne Point.

Baseline Oil Recovery (BOR) or Baseline Recovery (BR): 

It is the oil recovered by means of unassisted natural depletion-drive mechanisms using conventional vertical wells and completions. Mechanisms include solution-gas drive, fluid expansion, aquifer drive, gas-cap expansion, and/or rock compaction.

Assisted Oil Recovery (AOR)

• Surface-Controlled Recovery (SCR) or Reservoir Access Enhancements (RAE)
• This name reflects the methods that manage and optimize recovery through surface-level interventions and well operations, focusing on enhancing the wellbore or surface facilities rather than altering the reservoir itself. It includes:
  • Pattern and fluid sweep adjustments
  • Drilling and well intervention
  • Production Mechanics
• They can be applied at any time during the field’s life.
• Subsurface Injection Recovery (SIR) Or Injection-Based Enhancements (IBE)
• This category encompasses all methods that involve injecting fluids into the reservoir to enhance oil recovery. These techniques are further divided based on whether the injected fluids are native to the reservoir or non-native.
  • Native Fluid Injection (NFI)
    • Definition: This subcategory includes recovery methods where the injected fluids are naturally occurring in the reservoir. The primary purpose of these techniques is to maintain reservoir pressure and improve displacement efficiency by reintroducing the same types of fluids that the reservoir originally contained.
    • Key Techniques:
      • Water Injection: Reinjection of produced water or other water sources to maintain pressure.
      • Gas Injection: Reinjection of produced gas, such as natural gas or associated gas, to enhance oil recovery.
  • Non-Native Fluid Injection (NNFI)
    • Definition: This subcategory involves the injection of fluids that are not originally present in the reservoir. These techniques typically aim to alter the reservoir’s characteristics or the fluid properties within it to improve oil recovery.
    • Key Techniques:
      • Chemical Injection: Polymer (+SP/ASP) flooding, microbial enhanced oil recovery (MEOR).
      • Gas Injection (Non-Native): CO2 injection, nitrogen injection, hydrocarbon gas injection (e.g., propane, butane), Water-Alternating-Gas (WAG).
      • Thermal Methods: Steam injection, in-situ combustion, cyclic steam injection, SAGD (Steam Assisted Gravity Drainage).
      • Other Energy-Based Techniques: Microwave energy, acoustic wave energy.

By focusing on the nature of the intervention rather than adhering to traditional stages of recovery (primary, secondary, tertiary), these names simplify the approach and avoid the pitfalls of segmenting production into too many rigid stages. Such an approach moves away from the myopic focus on optimizing Net Present Value (NPV) by stage and instead emphasizes optimizing the full lifecycle of the reservoir. By doing so, we open up the possibility of achieving higher recovery rates, reducing water production, and addressing conformance issues before they become insurmountable—all by leveraging the full range of available techniques in a more cohesive and strategically sound manner. However, we must acknowledge that changing established terminology and practices will not be easy. The power of words and the frameworks they create in our minds is immense, influencing how we approach challenges and make decisions. Yet, with the work already begun and the momentum building, this could be the right moment to reexamine and reshape the language and strategies we use in oilfield development. This is an opportunity to align our practices with the realities of today’s industry and set a course for greater efficiency and success in the future.