Assessment of Friction Reducer Performance Within a Continuous Brine Spectrum

The performance of friction reducers in standard flow loops is a function of the specific friction reducer, environmental factors such as brine composition and fluid temperature, and the unique loop design and run procedure. This study examines the performance of various commercial and experimental friction reducers using Design of Experiments with variables of friction reducer loading expressed in gallons per thousand gallons, brine Total Dissolved Solids expressed in parts per million, and R+ Hardness expressed as the mole ratio of cationic hardness ions to the Total Dissolved Solids in decimal percentage. The ultimate percent friction reduction is generally dependent upon these variables, and each friction reducer generates unique profiles used to predict performance within the above variable space. This study evaluated 12 inverse emulsion friction reducers of various charge types in a 100 foot once through pipe. For this design of study, the Total Dissolved Solids was varied from 5,000 to 150,000 parts per million, the R+ Hardness varied from 0.0 to 0.3, and the friction reducer loading varied from 0.25 to 1.00 gallons per thousand gallons. Each reducer was injected into a reservoir containing a brine with the previously referenced, pre-established levels of Total Dissolved Solids and R+ Hardness, and the resulting maximum percentage friction reduction calculated by standard differential pressure protocol. The response surfaces generated had Ajusted-R2 values from 0.86 to 0.99 demonstrating an exceptionally good fit for the chosen regression model. The contour profiles expressed a general similarity between related charge types with type of charge significantly influencing the response surface profile. Typically, as friction reducer loading increased, percent friction reduction increased or a maximum plateau was achieved, or performance declined. Certain friction reducers’ performances increased as Total Dissolved Solids and/or R+ Hardness increased whereas many reducers’ performances decreased. The gradient of the response surfaces varied from linear progressing to cubic functions with arithmetic transformations. How friction loop results transmute to full scale hydraulic fracturing operations is not yet fully understood and no delineated process currently exists. However, mapping response surfaces of specific friction reducers then comparing responses to other friction reducers’ response data provides insight and can articulate how reducers’ performances are affected by friction reducer loading, TDS, and R+ Hardness, particularly in operations involving highly variable water quality. As brine character can vary during a hydraulic fractioning treatment, the best practice may be to either use a friction reducer known to perform well within the expected brine level or anticipate using multiple friction reducers for a specific treatment.