Drilling system with mud motor including mud lubricated bearing assembly

A method of drilling a wellbore, the method comprising:

• pumping drilling fluid down a drillstring within the wellbore to operate a drill bit, the drillstring including a mud motor, a bearing assembly, and a rotary steerable system (RSS);
• rotating a driveshaft comprising a bore of the bearing assembly with the mud motor to rotate the drill bit and drill the wellbore;
• supporting the rotation of the driveshaft with the bearing assembly;
• diverting a portion of the drilling fluid from the bore of the driveshaft through a bypass fluid flowpath through bearings of the bearing assembly;
• restricting flow of the drilling fluid into the bypass fluid flowpath using a choke assembly in the bypass fluid flowpath;
• flowing at least some of the diverted drilling fluid past the choke assembly and into an annulus in the wellbore outside of the bearing assembly through an unsealed annulus port;
• recapturing at least some of the diverted drilling fluid into the bore from the bypass fluid flowpath through a return flowline;
• and
• extending pads of the RSS using the drilling fluid in the bore to push a drill bit to drill the wellbore in a desired direction using the drilling fluid flowing through the bore.

A bearing assembly for operation with a drillstring including a mud motor and a rotary steerable system (RSS) powered by drilling fluid, the bearing assembly comprising:

• a driveshaft including a bore and rotatable by the mud motor;
• bearings positioned circumferentially around the driveshaft and operable to rotationally support rotation of the driveshaft;
• a bypass fluid flowpath open for drilling fluid to divert from the bore of the driveshaft and flow through the bearings;
• and
• a choke assembly positioned in the bypass fluid flowpath and operable to restrict flow of the diverted drilling fluid through the bypass fluid flowpath such that at least some of the diverted drilling fluid flows through an unsealed annulus port into an annulus in a wellbore outside of the bearing assembly and at least some of the diverted drilling fluid is recaptured from the bypass fluid flowpath through a return flowline in fluid communication with the drillstring.