Debris removal method and assembly

Abstract

A method of removing debris from a well is disclosed, comprising RIH to required depth with coiled tubing having at least one closed check valve, moving a sleeve through the check valve to hold it open, opening a flow control valve located on the coiled tubing below the check valve; then reverse circulating a fluid to entrain debris in the wellbore and bring it to surface through the coiled tubing, before releasing the sleeve from the check valve; and POOH with the at least one check valve returned to the closed configuration. By holding the check valves open, reverse circulation can be performed in the well using coiled tubing, so sufficient lift can be achieved to bring the debris to surface even in underbalanced or low pressure wells. Safety measures can be maintained by having at least one check valve in the conventional closed configuration on RIH and POOH. The flow control valve allows the check valve to be opened or closed without pumping any fluid into the well and thus the sleeve can be moved to hold the check valve open with a relatively low pressure.

1 . A method of removing debris from a well, the method comprising:
 running into the hole (RIH) to required depth with coiled tubing having at least one check valve arranged in a closed configuration;   at depth, applying a first pressure to move a sleeve through the at least one check valve to hold the check valve in an open configuration; applying a second pressure to open a flow control valve located on the coiled tubing below the check valve(s);   reverse circulating a fluid to entrain debris in the wellbore and bring it to surface through the coiled tubing; releasing the sleeve from the at least one check valve; and   pulling out of the hole (POOH) with the at least one check valve returned to the closed configuration.   
     
     
         2 . A method as claimed in  claim 1  wherein the second pressure to open the flow control valve is greater than the first pressure. 
     
     
         3 . A method as claimed in  claim 1 , wherein the first pressure is bled off to lock the at least one check valves in the open configuration. 
     
     
         4 . A method as claimed in  claim 1 , including the step of closing the flow control valve at depth to retain the debris within the coiled tubing prior to pulling out of hole. 
     
     
         5 . A method as claimed in  claim 1 , including the step of receiving a predetermined volume of debris-laden fluid into the coiled tubing. 
     
     
         6 . A method as claimed in  claim 1 , including the step of introducing a cleaning liquid to the coiled tubing between the flow control valve and the check valves prior to the coiled tubing being run in hole. 
     
     
         7 . A method as claimed in  claim 6 , wherein the cleaning liquid comprises a gel. 
     
     
         8 . A method as claimed in  claim 7 , including the step of flowing the gel into the well, at depth, when the second pressure is applied, to entrain the debris and hold it in suspension. 
     
     
         9 . A method as claimed in  claim 8 , including the step of running the coiled tubing in hole (RIH) to cause the suspended debris to flow into the coiled tubing. 
     
     
         10 . A method as claimed in  claim 9 , including the step of retaining the suspended debris in the coiled tubing by use of the fluid control valve. 
     
     
         11 . A method as claimed in  claim 10 , including the step of moving the check valves to the closed configuration by applying pressure. 
     
     
         12 . A method as claimed in  claim 8 , including the step of pulling the coiled tubing out of hole (POOH) and releasing the suspended debris from the space between the check valves and the flow control valve. 
     
     
         13 . A bottom hole assembly for running on coiled tubing, the assembly comprising:
 a selective check valve including a sleeve which can be positioned through the check valve and hold it in an open configuration; and   a flow control valve, the flow control valve comprising:
 a substantially cylindrical body having an internal bore providing an inlet at a first end and an outlet at an opposing end; 
 a flapper valve located in the internal bore towards the outlet, the flapper valve being arranged to open when a predetermined pressure is applied and to allow fluid flow through the flapper valve from the outlet to the inlet; 
 a hollow bore piston arranged adjacent the flapper valve in the internal bore, the piston including at least one port in fluid communication with the hollow bore; and 
 wherein when a pressure is applied to the piston, the piston moves towards the flapper valve and the at least one port aligns with at least one fluid flow path arranged in the body, bypassing the flapper valve, and exiting in the internal bore between the flapper valve and the second end. 
   
     
     
         14 . A bottom hole assembly as claimed in  claim 13 , wherein the piston is biased in a direction away from the flapper valve towards the inlet, by means of a resilient device. 
     
     
         15 . A bottom hole assembly as claimed in  claim 13 , wherein the pressure is determined by the force required to compress the resilient device between the piston and the body. 
     
     
         16 . A bottom hole assembly as claimed in  claim 13 , wherein the flow control valve is located below the at least one selective check valve and the bottom hole assembly is located towards an end of a coiled tubing. 
     
     
         17 . A bottom hole assembly as claimed in  claim 13 , comprising one or more of a group comprising: a disconnect sub, a kelly valve and a mule shoe guide. 
     
     
         18 . A bottom hole assembly as claimed in  claim 13 , having a plurality of check valves. 
     
     
         19 . A bottom hole assembly as claimed in  claim 13 , wherein the at least one check valve comprises a dual flapper arrangement. 
     
     
         20 . A bottom hole assembly as claimed in  claim 13 , wherein the flow control valve is a two-way valve opening at the predetermined second pressure to allow flow of fluid from the coiled tubing to the wellbore or to allow free flow from the wellbore to the coiled tubing when the at least one check valve is locked open. 
     
     
         21 . A bottom hole assembly as claimed in  claim 13 , wherein the flow control valve incorporates a separate reverse check valve. 
     
     
         22 . A bottom hole assembly as claimed in  claim 13 , wherein at least one piston is moved by pressure applied to two sealed areas of the piston, the sealed areas having different surface areas.