Stop Leaving Oil Behind: Molecular Weight Has Answers

New research shows high-molecular-weight HPAM can more than double oil recovery versus standard waterflooding in heterogeneous reservoirs

8 May 2026

A new study published in the journal Gels has found that the molecular weight of polymer additives used in oil recovery is the dominant factor in determining how much crude can be extracted from depleted reservoirs. The finding challenges the industry's conventional emphasis on viscosity when choosing chemical treatments.

Researchers Raupov, Kone, and Feinberg tested two variants of partially hydrolysed polyacrylamide, a widely used polymer, in laboratory core-flooding experiments designed to mimic heterogeneous reservoir conditions. Standard waterflooding recovered between 30 and 31 per cent of oil in place. Injection of high-molecular-weight polymer nearly doubled that figure, reaching approximately 62 per cent. A combined injection sequence achieved 74 to 76 per cent.

The performance gap stems from a property called viscoelasticity. Only the high-molecular-weight polymer displayed elastic behaviour inside porous rock, generating forces at narrow pore openings that dislodged oil trapped in zones bypassed by conventional flooding. Its lower-weight counterpart, lacking this characteristic, recovered roughly 40 per cent of oil in place. Rheology tests confirmed that the elastic response varied with pore size, salt content, and temperature, pointing to the need for reservoir-specific analysis before any field deployment.

The findings carry practical weight for US operators managing mature fields. Chemical enhanced oil recovery has attracted renewed interest as constraints on carbon dioxide supply and the cost of pipeline infrastructure have created headwinds for gas-injection programmes across basins including the Permian and Midcontinent. Yet polymer selection has typically focused on matching viscosity rather than molecular weight, a practice the study suggests leaves meaningful recovery volumes on the table.

Operational hurdles remain. High-molecular-weight polymers can reduce the rate at which fluid enters a well, are susceptible to mechanical breakdown through wellbore equipment, and may perform unevenly in saline formations. The laboratory setting does not fully replicate field conditions, limiting how directly results translate to production decisions. Operators will require site-specific data before reallocating capital. The study does not resolve those questions, but it establishes molecular weight as a primary variable, not a secondary one, in chemical recovery design.