SURFACTANTS
Screening parameters tuned to familiar chemistry can be misjudged when there is a mismatch between the test and its ability to predict performance. If a test overlooks an important interaction, transport limitation or divergence between laboratory and use conditions, results will be misinterpreted. The risk is even greater with unfamiliar complex molecular structures.
A screen can mislead in either direction
A candidate can be cast aside due to an unremarkable screening result while still meeting the application requirement. Conversely, a candidate can win the screen and disappoint in use. A reversal between screening rank and application performance exposes a limit to the prediction capacity of the screen.
A 1983 US Bureau of Mines investigation compared four wetting tests for coal-dust control: capillary rise, sink time, contact angle and zeta potential. They found no significant correlation among their results.
Figure 2 – When to accept, test further or step
The difference was not simply experimental noise, as each method emphasised a different part of the wetting problem.
Capillary rise measured penetration of solution into porous coal beds, while the sink test was more useful for judging how readily finely ground coal could be dispersed into suspension. The authors therefore cautioned against treating‘ wetting’ as a single interchangeable property and recommended choosing the test according to the intended application. 2 This reinforces the importance of understanding the differences between screening tests in both the information they provide and the value of that information to an application.
While the study challenges an interchangeable wettability test, it does not establish application failure criteria or describe how to select the right wettability test for the application. Having a clear understanding of the application and failure criteria is critical to select a meaningful screening test and assess candidates.
Consider an application that requires removing a contaminant from a surface. The appropriate test will vary whether that system is bathroom soil on ceramic tile, oil on rock or wax on industrial equipment. Substrate, temperature, shear, contact time, etc., determine whether a wipe test, a dissolution test or a custom method is appropriate; whether the test belongs in an oven or on a stir plate and whether a result at one hour still holds at 24 hours.
Matching test conditions to use conditions is what makes a result predictive and it is the first thing the check below asks. No screen captures every nuance of an application, which is why a mismatch calls for examination rather than an immediate verdict on the test.
In a Bakken surfactant programme, interfacial tension between crude oil and reservoir water samples from three wells were evaluated before and after treatment with a surfactant package. Two wells with posttreatment interfacial tension( IFT) behaviour broadly consistent with the pre-job laboratory assessment produced > 70 % above forecast during the trials. A third well showed even lower post-treatment IFT but delivered only 35 % higher production.
The physical response was real, but the application outcome indicated that strong IFT reduction alone was not sufficient. The investigators attributed the mismatch to preferential surfactant placement into depleted zones rather than uniform treatment of productive intervals. 3
The example is useful because the screen was not wrong in measuring interfacial activity; it was incomplete as a predictor of production uplift without evidence that the chemistry contacted the productive rock volume.
The reverse risk is premature rejection when a familiar proxy
NOV / DEC 2026 SPECCHEMONLINE. COM
41