A regulated semi-flow downhole power system: model-based design and field evaluation

Electrical power availability and primary-battery consumption constrain modular bottomhole assembly (BHA) operation. This paper develops and evaluates a retrofit semi-flow mud-powered generator intended to supply compatible modular downhole tools during circulation and thereby reduce their reliance on primary lithium batteries. The engineering task combines hydraulic matching, regulated direct-current (DC) supply, interface adaptation, and management of drilling-fluid exposure. A survey identifies typical continuous loads of 10–35 W and dominant bus classes of 28 V and 36 V. A circulation-time scenario estimates approximately 35,300 battery cartridges per year in the battery-powered segment considered. The power unit combines an outer-rotor turbine alternator, a protected mud-lubricated bearing section, an SP-T rectifier/stabiliser and diagnostic logger, and an independent generator operating-hours recorder. A configuration-specific hydraulic-electromechanical model supports design screening for a 110-mm circulation tube and 77-mm rotor. Field summaries document 30 V-class regulation, with 91% of the SP-T recorded interval within 29–30 V; a separate recorder reports 259 h of generator operation and 78.2 million revolutions. The results support the feasibility of generator-supported circulation and a procedure for matching the power unit to a selected assembly. Battery-energy substitution is distinguished from total hydraulic-to-electric efficiency, which was not measured in the reported records.