Engineers routinely use heavy oil viscosity as one criterion for selection ofoptimum heavy oil exploitation methods, and to help predict the resultingproduction rates and project economics. Recent field and lab data suggest theseuses of oil viscosity haw been both over simplified and over valued. This maybe particularly true for empirically derived exploitation methods such as coldproduction using progressive cavity (PC) pumps. In some cases the consequencesof this misuse were poorer than expected field results and an anti-heavy oilsentiment among management.
Techniques for obtaining the most representative heavy oil Viscositymeasurements for a reservoir are discussed. Topics covered include: sampling, handling, cleaning, lab procedures, oil compositional effects, live vs dead oilviscosities, and oil viscosity variation within a reservoir. This informationcan be used to determine if the existing oil viscosity data are valid, and toprovide guidelines for future heavy oil viscosity measurements.
Western Canadian heavy oil and bitumen reservoirs have been exploited withvarying degrees of success for more than 45 years1. During that timeproducers searched for easily measured parameters that allowed accurateprediction of oil production rates and cumulative volumes. Oil viscosity hasbeen used for this purpose, but the accuracy of the resulting productionforecasts was often disappointing.
From the perspective of the engineer, understanding and trusting viscosityvalues is challenging. He or she probably has a limited background in organic, physical, and analytical chemistry, and little time for formal training inthese areas. This situation is likely even more difficult in smaller oilcompanies, where in-house experts are not available for consultation. Ifviscosity data exist, but you feel they may not be accurate, another challengeis management's tendency to resist spending money for ‘duplicate lab tests’ orfor more costly ‘excessively rigorous’ data collection methods.
This study was conducted to address these concerns. The selected approach wasto de-emphasize theory, as it is well documented in theliterature2–4. Instead, we have emphasized a practical approach foruse by production and reservoir engineers.
Factors other than viscosity that affect heavy oil and bitumen producibility are not considered in this paper due to spaceconsiderations, but the reader should be aware of them. Examples are: reservoirheterogeneity5, water encroachment6, formation of viscousemulsions7, pumping problems8, and scaleformation9.
General Considerations: If your employer is not willing to pay for a'best effort' collection of a representative sample, there is little point inconducting an oil viscosity study. The viscosity obtained will be more likelyto mislead than guide you.
Unless you are willing and able to go to the field and collect the sample(s)yourself this exercise must be entrusted to field personnel. The best methodof assuring the task is completed correctly is through clear communication.Everyone is busy in the leaner oil patch, and staff must be informed of thesignificance of the procedures you request.