Hydrostatically balanced modulator assembly and associated method for mud pulse telemetry

A hydrostatically compensated modulator assembly for generating pressure wave fluctuations in drilling fluid flow, the hydrostatically compensated modulator assembly comprising:

• a housing having two or more drilling fluid flow passages, each passage of the two or more drilling fluid flow passages configured as either (a) a gap between an inner surface of the housing and an outer surface of a chamber within the housing, or (b) an elongated slot in a supporting plate fastened to the chamber within the housing;
• the chamber within the housing filled with hydraulic oil;
• two or more reciprocating members disposed substantially perpendicular to a wellbore axis and at least partially within the chamber, each reciprocating member of the two or more reciprocating members operatively associated with a respective drilling fluid flow passage and operatively connected to an obstruction portion that is positioned to partially or completely obstruct said drilling fluid flow passage during operation, wherein said connection transmits lateral movement from the reciprocating member to the obstruction portion for obstruction of the passage while permitting axial freedom of relative motion, such that kinetic energy resulting from drilling fluid flow acting on the obstruction portion is diverted primarily to a fixed surface of a chamber body of the chamber;
• a piston located at a lower portion of the chamber, a base of the piston being directly exposed to the drilling fluid, so that pressure exerted by the drilling fluid is transmitted to the hydraulic oil within the chamber, thereby maintaining an approximate hydrostatic balance between oil pressure inside the chamber and a drilling fluid pressure outside the chamber;
• a motor and a gearbox assembly operatively coupled to a linear actuator for converting rotary motion into axial displacement of the piston, wherein a power rating of the motor and a gearbox ratio are selected so that the linear actuator is capable of moving the piston by a predetermined distance within either (a) a half-period of a highest frequency utilized for pressure signal encoding, or (b) a minimum time required to fully open or close the respective drilling fluid flow passage for individual pressure pulse generation;
• a controller programmed to regulate movement of the two or more reciprocating members, controlling obstruction of the drilling fluid flow passages to produce pressure fluctuation waves, wherein the controller is configured to select and implement a signal encoding scheme chosen from at least one of:
• (i) alphabet frequencies combinatorial encoding, (ii) carrier frequency modulation, or (iii) single pulse sequence generation, and further configured to change the signal encoding scheme or adjust parameters of the signal encoding scheme in response to downlinking instructions received from a surface, wherein the controller is capable of operating the hydrostatically compensated modulator assembly to generate pressure signals sufficient for high-speed data transmission.