Subsea well systems and methods for controlling fluid from the wellbore to the surface

1. A subsea wellbore system wherein a return fluid flows from a wellbore to a surface via an annulus between a drill string and a casing and then an annulus between the drill string and a riser, the system comprising:

an annular closure device along the riser above a blow-out preventer stack, the annular closure device configured to close the annulus between the drill string and the riser during drilling of the wellbore;

a bypass line connecting the annulus below the blow-out preventer stack to the surface, wherein the bypass line diverts the return fluid from the closed annulus below the blow-out preventer stack to the surface during drilling of the wellbore;

a ram along the bypass line configured to be in an inactive state when the annular closure device closes the annulus and configured to activate to close the flow of the return fluid through the bypass line in response to a kick occurring while the annular closure device is closed; and

a pump in the bypass line configured to pump fluid from a mud tank into the bypass line to maintain a hydrostatic pressure in the wellbore above a formation pressure.

2. The system of claim 1 further comprising a flow control device configured to restrict flow of the return fluid through the bypass line.

3. The system of claim 1 further comprising a control unit configured to: (i) determine a parameter of interest from a sensor in the system; and (ii) control the ram and the flow control device in response to the determined parameter of interest.

4. The system of claim 3 , wherein the parameter of interest is kick and wherein the sensor is located at one of: (i) in the bypass line below the ram; (ii) in the annulus below the annular closure device; (iii) in the wellbore; and (iv) in an assembly used for drilling the wellbore.

5. The system of claim 3 further comprising a flow control device for controlling back pressure in the wellbore when the return fluid is flowing through the bypass line.

6. The system of claim 1 further comprising a sensor for determining closure of the ram.

7. The system of claim 1 further comprising a sensor for providing information about position of the ram and a control unit that controls the position of the ram in response to detection of a kick in the wellbore.

8. The system of claim 1 further comprising a fluid supply unit that supplies a fluid into the bypass line against the fluid flow direction of the return fluid in the bypass line when the return fluid is temporarily stopped from flowing through the bypass line.

9. A subsea wellbore system, comprising:

a subsea wellhead including an annular closure device for closing an annulus of the wellbore during drilling of the wellbore;

a bypass line for returning fluid from below the annular closure device to a surface location;

a ram along the bypass line configured to be in an inactive state when the annular closure device closes the annulus and configured to shut in the bypass line in response to a kick occurring in the wellbore while the annular closure device is closed;

a first sensor for determining a position of the ram;

a second sensor for providing measurements relating to a kick in the wellbore;

a subsea control unit that determines presence of the kick in the wellbore occurring when the annular closure device is closed from the measurements from the second sensor and controls the position of the ram in response to the determined kick; and

a pump in the bypass line configured to pump fluid from a mud tank into the bypass line to maintain a hydrostatic pressure in the wellbore above a formation pressure.

10. The system of claim 9 , wherein the second sensor is placed at a location selected from a group consisting of: below the ram; in an assembly used for drilling the wellbore; and inside the wellbore.

11. The system of claim 9 , wherein the subsea control unit transmits information to a surface controller about the presence of the kick and controls the ram in response to instructions received from the surface controller.

12. A method of controlling flow of a fluid from a subsea wellbore to surface during drilling of a wellbore wherein a fluid supplied from a surface location into a drill string returns from the wellbore to the surface via an annulus between the drill string and a casing and then an annulus between the drill string and a riser above a blow-out preventer, the method comprising:

activating an annular closure device above the blow-out preventer during drilling to close an annulus between the drill string and the riser, thereby preventing flow of the return fluid through the annulus; and

flowing the return fluid to the surface via a bypass line connecting the annulus below the blow-out preventer to a surface location when the annular closure device is activated drilling of the wellbore;

activating a ram along the bypass line in response to a kick while the annular closure device is closed during drilling operations in order to close the bypass line to prevent flow of the return fluid through the bypass line; and

activating a pump in the bypass line to pump fluid from a mud tank into the bypass line to maintain a hydrostatic pressure in the wellbore above a formation pressure.

13. The method of claim 12 further comprising closing the flow of the return fluid through the bypass line upon determining a parameter of interest.

14. The method of claim 13 further comprising closing the blow-out preventer along with the ram in the bypass line upon determining the parameter of interest to prevent flow of the return fluid beyond the blow-out preventer.

15. The method of claim 12 , wherein determining the parameter of interest comprises using measurements from a sensor located at one of: in the bypass line; in a drilling assembly utilized for drilling the wellbore; and a location below the blow-out preventer.

16. The method of claim 12 further comprising determining flow of the fluid through the bypass line after closing the bypass line to determine effectiveness of the closure of the bypass line.

17. The method of claim 12 further comprising controlling flow of the return fluid through the bypass line to control back pressure in the wellbore when the bypass line is open.

18. The method of claim 12 further comprising confirming closing the ram utilizing signals from a position sensor in the ram.

19. The method of claim 12 further comprising:

stopping supply of the fluid from the surface into the drill string upon detection of a kick; and

supplying a fluid from the surface into the bypass line in a direction opposite direction of the return fluid in the bypass line to manage pressure in wellbore.