Grease injection system for riserless light well intervention

Abstract

A subsea lubricator system is disclosed which includes a lubricator tube adapted to be positioned subsea above a subsea well, a pressure control head adapted to be positioned above the lubricator tube, at least one pressure sensor adapted for sensing at least one of a pressure in the subsea well or an ambient seawater pressure proximate the pressure control head, and at least one pump that is adapted to be positioned subsea to inject a lubricant into the pressure control head at a pressure that is greater than the sensed pressure. A method of operating a subsea lubricator system positioned above a subsea well, the lubricator system including a pressure control head, is also disclosed which includes monitoring at least one of a pressure within the well and an ambient seawater pressure proximate the lubricator system, and injecting a lubricant into the pressure control head at a pressure that is greater than the monitored pressure.

1 . A method of operating a subsea lubricator system positioned above a subsea well, said lubricator system comprising a pressure control head, the method comprising:
 monitoring at least one of a pressure within said well and an ambient seawater pressure proximate said lubricator system; and   injecting a lubricant into said pressure control head at a pressure that is greater than said monitored pressure.   
   
   
       2 . The method of  claim 1 , wherein the method comprises monitoring both of the pressure in the well and the ambient seawater pressure and monitoring a pressure within the pressure control head. 
   
   
       3 . The method of  claim 2 , wherein the step of injecting a lubricant into the pressure control head is performed at a pressure that is a set value greater than both of the monitored well pressure and the monitored ambient seawater pressure. 
   
   
       4 . The method of  claim 2 , wherein the step of injecting a lubricant into the pressure control head is performed at a pressure that is a set value greater than at least one of the monitored well pressure and the monitored ambient seawater pressure. 
   
   
       5 . The method of  claim 1 , further comprising actuating at least one pump that is positioned subsea to inject said lubricant into said pressure control head at said pressure that is a set value greater than said monitored pressure. 
   
   
       6 . The method of  claim 1 , wherein said lubricant is obtained from an accumulator that is positioned subsea and contains said lubricant. 
   
   
       7 . The method of  claim 1 , wherein said lubricant is a petroleum based lubricant. 
   
   
       8 . The method of  claim 1 , wherein said lubricant is a non-hydrocarbon containing lubricant. 
   
   
       9 . The method of  claim 1 , wherein said lubricant is a bio-degradable lubricant. 
   
   
       10 . The method of  claim 1 , wherein said lubricant comprises fish oil. 
   
   
       11 . The method of  claim 5 , further comprising actuating at least one additional pump that is positioned subsea to inject said lubricant into said pressure control head at said pressure that is a set value greater than said monitored pressure. 
   
   
       12 . The method of  claim 11 , further comprising injecting said lubricant into said pressure control assembly at two spaced apart locations. 
   
   
       13 . The method of  claim 5 , wherein actuating said at least one pump comprises actuating said at least one pump using battery power. 
   
   
       14 . The method of  claim 5 , wherein said at least one pump is operatively coupled to a battery power source and a power cable supplied from a surface vessel or platform, and wherein said at least one pump may be actuated using electrical power supplied from either said battery power source or from said power cable. 
   
   
       15 . The method of  claim 1 , wherein injecting a lubricant into said pressure control head comprises injecting a lubricant into said pressure control head at a pressure that is at least 15 psi greater than the monitored pressure. 
   
   
       16 . A method of operating a subsea lubricator system positioned above a subsea well, said lubricator system comprising a pressure control head, the method comprising:
 monitoring at least one of a pressure within said well and an ambient seawater pressure proximate said lubricator system;   injecting a lubricant into said pressure control head at a pressure that is a set value greater than said monitored pressure; and   obtaining said lubricant from an accumulator that is positioned subsea and contains said lubricant.   
   
   
       17 . The method of  claim 16 , wherein the method comprises monitoring both of the pressure in the well and the ambient seawater pressure and monitoring a pressure within the pressure control head. 
   
   
       18 . The method of  claim 17 , wherein the step of injecting a lubricant into the pressure control head is performed at a pressure that is a set value greater than both of the monitored well pressure and the monitored ambient seawater pressure. 
   
   
       19 . The method of  claim 16 , further comprising actuating at least one pump that is positioned subsea to inject said lubricant into said pressure control head at said pressure that is a set value greater than said monitored pressure. 
   
   
       20 . The method of  claim 16 , wherein said lubricant is a non-hydrocarbon containing lubricant. 
   
   
       21 . The method of  claim 16 , wherein said lubricant is a bio-degradable lubricant. 
   
   
       22 . The method of  claim 16 , wherein said lubricant comprises fish oil. 
   
   
       23 . The method of  claim 19 , further comprising actuating at least one additional pump that is positioned subsea to inject said lubricant into said pressure control head at said pressure that is a set value greater than said monitored pressure. 
   
   
       24 . The method of  claim 19 , further comprising injecting said lubricant into said pressure control assembly at two spaced apart locations. 
   
   
       25 . The method of  claim 19 , wherein actuating said at least one pump comprises actuating said at least one pump using battery power. 
   
   
       26 . The method of  claim 19 , wherein said at least one pump is operatively coupled to a battery power source and a power cable supplied from a surface vessel or platform, and wherein said at least one pump may be actuated using electrical power supplied from either said battery power source or from said power cable. 
   
   
       27 . The method of  claim 16 , wherein injecting a lubricant into said pressure control head comprises injecting a lubricant into said pressure control head at a pressure that is at least 15 psi greater than the monitored pressure. 
   
   
       28 . A subsea lubricator system, comprising:
 a lubricator tube adapted to be positioned subsea above a subsea well;   a pressure control head adapted to be positioned above said lubricator tube;   at least one pressure sensor adapted for sensing at least one of a pressure in said subsea well or an ambient seawater pressure proximate said pressure control head; and   at least one pump that is adapted to be positioned subsea to inject a lubricant into said pressure control head at a lubricant pressure that is greater than said sensed pressure.   
   
   
       29 . The system of  claim 28 , further comprising a lubricant accumulator that is adapted to be positioned subsea and contain said lubricant to be injected into said pressure control head. 
   
   
       30 . The system of  claim 28 , wherein said lubricant pressure is greater than said sensed pressure by a set value. 
   
   
       31 . The system of  claim 30 , wherein said set value is at least 15 psi. 
   
   
       32 . The system of  claim 29 , further comprising a lubricant return line that extends between said pressure control head and a used lubricant container. 
   
   
       33 . The system of  claim 28 , further comprising a control system that is adapted to be positioned subsea, said control system adapted to receive said sensed pressure and actuate said at least one pump in response to said sensed pressure. 
   
   
       34 . The system of  claim 33 , wherein said control system controls said at least one pump such that said lubricant pressure is greater than said sensed pressure by a set value. 
   
   
       35 . The system of  claim 33 , wherein said control system is adapted to regulate a pressure of the lubricant injected into the pressure control head. 
   
   
       36 . The system of  claim 28 , wherein said system comprises at least two pumps that are adapted to be positioned subsea, each of which are adapted to inject liquid into said pressure control head. 
   
   
       37 . The system of  claim 36 , wherein said first and second pumps are adapted to inject said lubricant into said pressure control head at spaced apart locations. 
   
   
       38 . The system of  claim 28 , wherein said system further comprises a battery that is adapted to be positioned subsea, said battery adapted to supply electrical power to said at least one pump. 
   
   
       39 . The system of  claim 38 , wherein said system further comprises an umbilical from a surface vessel or platform that is adapted to supply electrical power to said at least one pump. 
   
   
       40 . The system of  claim 28 , wherein said system comprises at least one pressure sensor for sensing a pressure within said subsea well, at least one pressure sensor for sensing a pressure of said ambient seawater, and at least one pressure sensor for sensing a pressure within the pressure control head.