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A system for reverse circulation in a wellbore includes equipment for supplying drilling fluid into the wellbore bit via at least an annulus of the wellbore and returning the drilling fluid to a surface location via at least a bore of a wellbore tubular. The system also includes devices for controll

A system for reverse circulation in a wellbore includes equipment for supplying drilling fluid into the wellbore bit via at least an annulus of the wellbore and returning the drilling fluid to a surface location via at least a bore of a wellbore tubular. The system also includes devices for controlling the annulus pressure associated with this reverse circulation. An active pressure differential device may increase the pressure wellbore annulus to at least partially offset a circulating pressure loss. Alternatively, the system may include devices for decreasing the pressure in the annulus of the wellbore.

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1. A method for reverse circulating a drilling fluid in a wellbore, comprising: supplying drilling fluid into the wellbore via at least an annulus of the wellbore;returning the drilling fluid to a surface location via at least a bore of a tubular;increasing a pressure in the circulating returning fl

1. A method for reverse circulating a drilling fluid in a wellbore, comprising: supplying drilling fluid into the wellbore via at least an annulus of the wellbore;returning the drilling fluid to a surface location via at least a bore of a tubular;increasing a pressure in the circulating returning fluid using an Active Pressure Differential Device (APD Device) in the wellbore;flowing the drilling fluid from the annulus into the tubular via a second APD device in the wellbore;varying a pressure in the circulating drilling fluid using the second APD Device; andcontrolling the second APD Device using a selected formation parameter. 2. The method according to claim 1, further comprising: estimating a circulating pressure loss; andincreasing the pressure in the drilling fluid supplied into the annulus of the wellbore to at least partially offset the circulating pressure loss. 3. The method according to claim 1 wherein the second APD Device increases the pressure in drilling fluid supplied into the annulus of the wellbore to at least a pore pressure of a formation intersected by the wellbore. 4. The method according to claim 1 wherein the selected formation parameter is one of (i) a pore pressure of a formation intersected by the wellbore, and (ii) a fracture pressure of a formation intersected by the wellbore. 5. The method according to claim 4 further comprising: supplying a fluid to the wellbore via a riser; and adjusting a height of the fluid in the riser to decrease the pressure in the annulus of the wellbore. 6. The method according to claim 4 further comprising: positioning a fluid supply at a selected subsea location; and supplying the fluid into the wellbore from the fluid supply. 7. The method according to claim 1 further comprising: determining a pore pressure of a formation intersected by the wellbore; and selecting a weight for the drilling fluid that causes a wellbore pressure greater than the determined pore pressure during fluid circulation. 8. The method of claim 1, wherein the APD Device is bi-directional. 9. A system for circulating a fluid in a wellbore wherein the fluid flows into the wellbore at least via a wellbore annulus and returns to the surface via at least a bore of a wellbore tubular, the system comprising: a fluid circulation device in a fluid returning to the surface, the fluid circulation device providing the primary motive force for flowing the fluid to the surface;a flow control device in the wellbore conveying fluid from the annulus into the wellbore tubular, the flow control device being configured to control a flow of fluid circulating through the wellbore annulus and through the fluid circulation device to control pressure in the wellbore; anda controller configured to control the flow control device using a selected formation parameter. 10. The system of claim 9 wherein the flow control device is an active pressure differential device that increases a pressure in the fluid flowing in the annulus to at least partially offset a circulating pressure loss caused by operation of the fluid circulation device. 11. The system of claim 9 further comprising: a fluid supply positioned at a selected subsea location that supplies the drilling fluid. 12. The system of claim 9 further comprising: a riser supplying a fluid to the wellbore, wherein the flow control device adjusts a height of the fluid in the riser to decrease the pressure in the annulus of the wellbore. 13. The system of claim 9 wherein the fluid circulation device is a pump and the flow control device is a pump. 14. The system of claim 9, wherein the fluid circulation device is bi-directional.