Abstract
High density brines can provide increased hydrostatic pressure when used as cleanout fluids in coiled tubing operations. Due to the high viscosities of brines and the small diameter of coiled tubing, friction pressure loss will offset the additional hydrostatic pressure exerted by high density brines and lead to serious limitations in job design. One solution is to apply a friction reducer. Most commercial friction reducers are designed for water or low density fluids; their solubility and dispersion characteristics in high density brines are usually not acceptable. Additionally, high salt content and low free water in brines can diminish the effectiveness of a friction reducer. Many papers have been published on friction reducers in water or low density fluids in straight tubing and coiled tubing, but few have addressed friction reducers in high density brines. Evaluating a friction reducer normally requires full-scale flow loop testing, which requires a large volume of brine and prevents thermal evaluation of friction reducers.
This study used a newly designed coiled small-diameter tubing (CSDT) flow loop to evaluate the properties of friction reducers in high density brines. The study evaluated two conventional friction reducers in brines including NaCl, CaCl2, NaBr, and CaBr2 with densities from 10.0 to 14.2 ppg. The study presents results from both CSDT and full-scale flow loop tests and demonstrates that the CSDT flow loop is a simplified and effective setup that can qualify friction pressure loss in tubing and evaluate the effectiveness of a friction reducer in high density brines. Heat-aging tests also investigated thermal degradation of friction reducers in brines. The tests can eliminate some commonly used friction reducers for high temperature applications due to thermal degradation. A case history is presented which successfully applied a friction reducer in an 11.0 ppg CaCl2 brine for a coiled tubing cleanout at 400°F.
