Comparison of Two SEM-EDX Methods for the Analysis of Produced WaterScale Filter Papers

摘要

Low-vacuum scanning electron microscopy(SEM)/energy dispersive x-ray(EDX)analysis can be usedto characterize the nature of inorganic scale from produced water(Method 1);routinely used to visuallydetermine the degree,form and composition of scale particulates.Quantitative data on scale coveragecan be extracted through image analysis,and morphology can indicate origins of particulates(transportedscale,active scale…).Recent trends demand more detailed quantitative analysis,believed to produce moreaccurate/reproducible results.Such a method is automated SEM-EDX particle analysis(Method 2).This has the advantage of full automation and delivers quantitative data on scale coverage,composition,shape and size.Neither method is perfect,the first relies on experienced SEM users,is a manual method,susceptible to bias,and is often perceived as producing qualitative data,while the second method althoughproducing large quantitative data sets,depends upon the criteria used to classify particles,and can betime consuming.Both methods were used to examine a number of filtered produced water samples.Thetraditional manual method provides good representative results on scale coverage,details on particulatemorphology and composition,and can be undertaken in about thirty minutes per sample;it is also a simplematter to differentiate between particulate and blanket scale deposits.The second method generates superiorlevels of quantitative data,but results are dependent on image thresholding(for particle selection),erroneousmisleading results are all too easily obtained(unless rigorously tested particle classification schemes areused),and the method can take in excess of an hour per sample.In general Method 1 should be adequateto track scale issues from produced water,which can be supplemented where desired by automated particleanalysis(APA).Where APA is to be used it is recommended that an industry standard classification criterionbe developed,which will increase the degree of confidence that can be applied to results,and allow directcomparison of results between laboratories.