Optimization of drag reduction performance and energy efficiency enhancement of polyethylene oxide in oil-water two-phase flow using response surface methodology

Abstract Drag reduction (DR) in oil–water two-phase flow by high-molecular-weight polymers offers a promising route to energy-efficient pipeline transport, yet quantitative multi-factor optimization remains underdeveloped. Here, we experimentally investigate the DR performance of polyethylene oxide (PEO, Mw = 1 × 10⁶ g/mol) in a horizontal oil–water flow loop (inner diameter 5 cm, test length 10 m) using a three-factor Box–Behnken response surface methodology design (15 runs). Rheological measurements confirm that 50–250 ppm PEO solutions exhibit weak non-Newtonian behavior with negligible viscosity increase (< 3.3 mPa·s at 250 ppm), verifying a viscoelastic DR mechanism. The reduced quadratic model achieves an adjusted R² of 0.9979 and a predicted R² of 0.9895, with all prediction errors within ± 3%. Analysis of variance identifies oil flow rate as the dominant negative factor (49.0% contribution), while polymer concentration and water flow rate exhibit positive saturating and peaking effects, respectively. Global optimization yields a maximum DR > 65% and a corresponding flow increase ≈ 40% at water flow rate 30–40 L/min, oil flow rate 2–4 L/min, and PEO concentration 150–200 ppm. The validated predictive framework provides an engineering tool for injection-strategy design and energy-efficiency improvement in multiphase crude-oil gathering pipelines.