GB2616787A

GB2616787A - A system and method for circulating drilling fluid in connection with open water drilling

Info

Publication number: GB2616787A
Application number: GB2309678.7A
Authority: GB
Inventors: A Potter Paul; Dale John
Original assignee: Electrical Subsea and Drilling AS
Current assignee: Electrical Subsea and Drilling AS
Priority date: 2021-01-12
Filing date: 2021-12-22
Publication date: 2023-09-20
Also published as: NO20210037A1; WO2022154666A1; NO346362B1; GB202309678D0

Abstract

The document presents a system and a method for circulation and well control in case of hydrocarbon influx from the reservoir formation during drilling with an open water drilling system. A fluid lift assistance feature is provided in a drilling fluid return riser, arranged as eductors, to reduce the dependence on a subsea pump to provide improved fluid lift to the surface. Implementation of subsea chokes with the subsea BOP facilitates circulation back to surface via the drilling fluid return riser, with kill-fluid supply via the drill-string as the primary pathway. Secondary pathways for supply of kill-fluid are provided in case the drill-string is sheared.

Claims

P a t e n t c l a i m s A circulation system for circulating drilling fluid contaminated with hydrocarbons to a surface system via a drilling fluid return riser (17) connected to a subsea wellhead (1) in connection with drilling in open water, the circulation system comprising: a blowout preventer (2) locked on the wellhead (1); a drill-string (9) extending from the surface down through open water and further to the bottom of a subsea well in an oil and gas reservoir; sealing devices (10, 11) connected on top of the blowout preventer (2), arranged to seal around the drill-string (9) in connection with the drilling operation; a control system connected to the blowout preventer (2) and arranged for detection of hydrocarbon influx from the well formation during the drilling operation; inlet ports of drilling chokes (23, 24) connected to a vertical centre-bore of the blowout preventer (2) and with outlets ports connected to the drilling fluid return riser (17); a drilling fluid return line spool (13) provided between well barriers of the blowout preventer (2) and the sealing devices (10, 11) forming alternative flow outlet connections to the drilling fluid return riser (17) via a pipe system (5, 7); a return line (4) arranged for flowing returned drilling fluid to the drilling fluid return riser (17) via a fluid-lift pump (16) arranged to lift the drilling fluid to the surface system via the drilling fluid return riser (17); c h a r a c t e r i z e d i n that one or more eductors (18) are installed in the drilling fluid return riser (17) to compensate for any limitations in the lifting capacity of the fluid-lift pump (16); a fluid-boost line (19) is arranged to provide a propellant fluid to anyone of the one or more eductors (18), the fluid-boost line being provided with sixth isolation valves (34) for controlling a propellant fluid flow to each of the one or more eductors (18); a connection point (30) for a temporary supply line in open water arranged for pumping of drilling fluid into the well from the surface via a BOP mounted well kill-line (32) with fifth-isolation valves (33A, 33B) to the vertical centre-bore of the blow-out preventer (2) through a connection port on the underside of a lower pipe-ram (25); and a secondary pathway for supply of drilling fluid from the surface to the connection port on the underside of the lower pipe-ram (25) of the blowout preventer (2), through an extension of the fluid-boost line (19) for propellant fluid to the one or more eductors (18).
2. A method for circulating drilling fluid contaminated with hydrocarbons to a surface system from a subsea well via a system according to claim 1 in connection with a need for well control and circulation of drilling fluid after unintentional influx of hydrocarbons into the well, c h a r a c t e r i z e d i n that the method comprising the steps of: a) detecting any influx of hydrocarbons by the control system connected to the blowout preventer (2); b) closing pipe-rams in the blowout preventer (2) to seal around the drill string (9); c) opening fourth isolation valves (29A, 29B) on the line connecting the vertical centre-bore of the blowout preventer (2) to the inlet of the drilling chokes (23, 24); d) opening one of the drilling chokes (23, 24), while drilling fluid is pumped down through the drill string (9); e) circulating out hydrocarbon-containing well fluid via a well annulus through one of the a drilling chokes (23, 24) on the blowout preventer (2) and further to the surface system via the fluid-lift pump (16) and the drilling fluid return riser (17); f) regulating the flowrate of the fluid-lift pump (16) as well as the opening of the active drilling choke (23, 24), so that the bottom hole pressure is kept higher than the pore pressure and lower than the fracturing pressure of the formation, while the contaminated drilling fluid is circulated out; g) assisting the fluid-lift pump (16) by operating one or more eductors (18) by pumping propellant fluid from the surface system through the fluid-boost line (19) and regulating the propellant fluid flow to each of the one or more eductors (18) via the control system.
3. The method according to claim 2, in case of a need to pump heavy drilling fluid into the well, after the drill string (9) has been sheared, the method comprising the steps of: h) connecting a supply line, in open water, from the surface system to the connection point (30) on the blowout preventer (2); i) opening the fifth isolation valves (33 A/B); and j) pumping heavy drilling fluid from the surface system via the open water supply line, the BOP mounted well kill-line (32) and openings in the lower part of the blowout preventer (2) to the annulus of the well .
4. The method according to claim 2 for pumping heavy drilling fluid into a well from a surface system after a drilling string (9) has been sheared, wherein the method comprises the further steps of: k) disconnecting anyone of the one or more eductors (18) by closing sixth isolation valves (34); I) opening any throttling devices at anyone of the one or more of the eductors (18) of the fluid-boost line (19); m) opening seventh isolation valves (36A, 36B) on the blowout preventer (2); and n) pumping the heavy drilling fluid from the surface system to the well an- nulus through the fluid-boost line (19), a second flexible hose (38), a connector (39), and further through the pipe arrangement and a first flexible hose (37), and through openings in the lower part of the blowout preventer (2).