Some oil field scales have the potential to contain regulated levels of naturally occurring radioactive materials (NORM). It is estimated that between 300,000 and 1,000,000 tons of NORM scale are produced each year. In addition, scale deposition in producing facilities negatively impacts rates of production and is expensive to treat and remediate. The most common NORM containing scale is BaSO4, or barite. This paper presents the results of a Gas Research Institute study that investigates the causes of NORM scale formation and mitigation techniques employed in the field.
Chemical threshold scale inhibitors are generally employed to inhibit scale formation in production systems. However, there is little agreement on which scale inhibitor is most effective with respect to differing water chemistries, temperatures and conditions encountered. Results using a GRI patented inhibitor evaluation apparatus can be used to determine the most effective inhibitor for a specific field application. Work in the Michigan Basin presented in the last conference indicated that a phosphinopolycarboxylate was most effective against NORM barium sulfate scale formation at low temperatures in relatively fresh water. Further work in this study identifies phosphonates as being more effective in the higher ionic strength (TDS) waters and higher temperature regimes that can be expected in the Gulf Coast. A matrix of ionic strength and temperatures with inhibition response is presented.
Although more NORM fields were studied, two are presented in detail. In these fields, three causes of NORM scale were identified;
Incipient scale in a well due to production;
Scale formation due to previous seawater floods and;
The commingling of waters from different zones or wells.
Field treatment techniques employed in the two fields studied are summarized in the paper.
Inhibitor squeeze procedures were also studied in the laboratory and in the field. A squeeze simulation apparatus was constructed to research inhibitor squeeze practices in the laboratory. Results from this work resulted in successful inhibitor squeeze applications in the field. The inhibitor squeeze apparatus and the field results are discussed in the paper. Squeeze life has been extended from an average of two to six months to two to three years or more as a result of the work.
As part of the introduction, it is appropriate to briefly describe the NORM problem and some of the vocabulary involved.