Rotary steerable system with active pad proportional control

A steering tool for drilling deviated wellbores, said steering tool having a generally cylindrical tool housing and a longitudinal tool axis, and further comprising:

• (a) a steering head having an upper end coaxially and co-rotatingly mountable to the tool housing, a lower end configured for connecting to a drill bit, and a steering head bore extending between said upper and lower ends of the steering head, and further comprising:
• (a1) two or more steering members arrayed around a circumference of the steering head, with each steering member having a longitudinal side edge pivotably mounted to an outer surface of the steering head;
• (a2) at each of one or more axially-spaced locations, a bank of two or more primary pistons circumferentially arrayed at a uniform angular spacing, wherein:
• when two or more banks of primary pistons are provided, all of the banks of primary pistons have the same number of primary pistons;
• each primary piston has a primary piston axis and is reciprocatingly movable within an associated primary piston chamber formed in the steering head, such that each primary piston is outwardly extendable to deflect an associated one of the steering members and thereby to exert a force against a wellbore being drilled by the drill bit;
• and
• the steering section defines a plurality of primary fluid supply channels equal in number to the number of primary pistons in each bank of primary pistons, wherein each primary fluid supply channel is in fluid communication with the one or more primary piston chambers at a selected one of the circumferential positions, and extends to the upper end of the steering head for conveying fluid for actuating the primary pistons at the selected circumferential position;
• and
• (a3) one or more banks of secondary pistons, with the secondary pistons in each bank of secondary pistons being equal in number to the number of steering members, and with each secondary piston having a secondary piston axis and being reciprocatingly movable within an associated secondary piston chamber formed in the steering head, such that each secondary piston is outwardly extendable to outwardly deflect a retraction tab on an associated steering member and thereby to urge the associated steering member toward a retracted position adjacent to the steering head, and wherein the steering head defines a plurality of secondary fluid supply channels equal in number to the number of secondary pistons, wherein each secondary fluid supply channel is in fluid communication with a selected one of the secondary piston chambers and extends to the upper end of the steering head for conveying fluid for actuating the selected secondary piston;
• (b) a fluid manifold having an upper end and a lower end, with the lower end of the fluid manifold being coaxially and co-rotatingly mountable to the upper end of the steering head, said fluid manifold defining:
• (b1) a plurality of primary manifold fluid passages equal in number to the number of steering members, with each primary fluid passage extending between a primary manifold fluid inlet port on the upper end of the fluid manifold and a primary manifold fluid outlet port on the lower end of the fluid manifold, with each primary manifold fluid outlet being in fluid communication with a selected one of the primary fluid supply channels of the steering head;
• (b2) a plurality of secondary manifold fluid passages equal in number to the number of steering members, with each secondary fluid passage extending between a secondary manifold fluid inlet port on the upper end of the fluid manifold and a secondary manifold fluid outlet port on the lower end of the fluid manifold, with each secondary manifold fluid outlet being in fluid communication with a selected one of the secondary fluid supply channels of the steering head;
• and
• (b3) one or more fluid bypass channels extending between an upper region of the fluid manifold and the lower end of the fluid manifold;
• (c) a valve section disposed within the tool housing, said valve section defining a valve section annulus between the valve section and the tool housing, and comprising:
• (c1) a rotationally geostationary primary valve defining a fluid chamber proximal to a lower end of the primary valve, with said lower end of the primary valve being engageable with the upper end of the fluid manifold such that the fluid chamber will be in fluid communication with the manifold fluid inlet ports;
• and
• (c2) a secondary valve disposed within the tool housing and configured to divert a portion of a fluid flow through the valve section annulus and to deliver the diverted fluid flow to the primary valve;
• wherein the primary valve comprises co-rotating flow restriction means configured to restrict the number of manifold fluid inlets in fluid communication with the fluid chamber at any given time as the fluid manifold and the steering head rotate relative to the primary valve, and wherein a non-diverted portion of the fluid flow in the valve section annulus can flow into the steering head bore via the one or more fluid manifold bypass channels.