Evaluation of Long-Term Scale Control for Shale and Tight Assets with Presence of Formation Rock

Abstract

Abstract Buildup of inorganic scales in O&G fields can cause significant production loss due to clogged near-wellbore formation and constrained production tubing. For Shale and Tight (S&T) assets, the damage in downhole formations can be rapid and permanent since the nanoscale pores cannot be recovered once filled with scale deposits such as barite. Production loss due to scale deposition can be up to 90% of total production compared to analog wells. Scale inhibitors (SI) are ideally used for scale control at nucleation and growth stages before its deposition. They can perform very differently depending upon application conditions, target scale types, treatment duration, treatment type, adsorption behavior, etc. Bottle tests are utilized to screen SI for various scale types and risk at selected conditions (up to 10 weeks) and to select best candidates. Adsorption studies (up to 12 weeks) were performed on the chosen chemicals to understand temporal change of SI residue concentration after contacting with formation rock during test period. In addition, a scale dissolver performance was evaluated for barite scale under different temperature and soaking times for scale remediation. Two phosphonate-based SI outperformed five other SI products in screening tests and were selected for adsorption studies. Formation rock samples from two wells which experienced production loss were mixed with SI treated fluid. SI residual continuously decreased in the first 2 days for all dosages between 50 ppm and 500 ppm. After 30 days, only ∼28% of added SI adsorbed on rock surfaces at 50 ppm. However, ∼50% adsorption of added SI was observed at 100, 250 and 500 ppm. For 250 ppm dosage, adsorption reached equilibrium in 7 days after which there was not a significant change in SI residual concentration. Performance of the tested scale dissolver improved when temperature and soaking time was increased, dissolving up to 82.6 Wt.% of barite mass. Correlation between temperature and dissolved Wt.% was generated to estimate performance at various temperatures. This study's SI adsorption results show that SI residual concentration at equilibrium is typically 30-50% of initial dosed SI. The results help improve our understanding of the interaction between chemicals and rock to better tune their dosage for long term scale control at subsurface. Scale dissolver results validated its performance and provided potential field application opportunities for scale remediation.