Drilling deep and ultra-deep wells under high-pressure/high-temperature (HPHT) conditions is a strategic pathway for expanding Ukraine’s resource base and requires a scientifically grounded approach to selecting optimal drilling-fluid formulations. The objective of this research was to establish, through an in-depth analysis of international and Ukrainian HPHT well construction practices, a methodology for selecting optimal formulations of high-performance water-based, clay-free drilling fluid systems (HT-HPWBF), which integrates both the hierarchy of optimality criteria and the system’s key performance indicators. A systematic review and content analysis of more than 200 publications on HT-HPWBFs were performed, the field experience from Ukrainian assets was synthesised, and a comparative analysis versus international practice was conducted. The assessment reveals that Ukraine lags behind leading HPHT regions primarily due to continued reliance on conventional KCl and biopolymer-potassium systems rather than modern HT-HPWBFs. Based on importance-impact analysis of requirements, technological constraints, and performance indicators, the study demonstrated the feasibility of constructing a hierarchical framework of core criteria for selecting optimal formulations. A three-tier optimality hierarchy comprising α -criteria (well-control and safety), β -criteria (achievement of technological objectives), and γ -criteria (environmental-economic effectiveness) was proposed. A methodology for constructing composite key performance indicators that integrate field experience, laboratory testing, and risk assessment was developed. The study substantiated the combined use of advanced analytics of historical data, real-time monitoring of fluid parameters, and key performance indicators driven decision making for formulation selection. The results can be directly applied by drilling engineers and service companies to improve the efficiency of HPHT well construction in Ukraine
Voloshyn et al. (Fri,) studied this question.