Control system and methods for moving a coiled tubing string at substantially constant rates

Abstract

A control system for a coiled tubing injector for moving a coiled tubing string within a wellbore, the injector including injector motors to power an injector drive mechanism, the injector drive mechanism engaging the coiled tubing to move the coiled tubing string, includes a controller for operating a power source to the injector motors to cause the injector drive mechanism to move the coiled tubing string within the well at a substantially constant rate.

What is claimed is: 
     
         1 . A control system for a coiled tubing injector for moving a coiled tubing string within a wellbore, the injector including injector motors to power an injector drive mechanism, the injector drive mechanism engaging the coiled tubing to move the coiled tubing string, the control system comprising a controller for operating a power source to the injector motors to cause the injector drive mechanism to move the coiled tubing string within the well at a substantially constant rate. 
     
     
         2 . The control system of  claim 1 , wherein the power source comprises a pump and a control valve for metering fluid flow. 
     
     
         3 . The control system of  claim 1 , wherein the controller is configured to operate a check valve that controls fluid communication between a first hydraulic flow line configured to operate the injector motors in a manner to move the coiled tubing into the well, and a second hydraulic flow line configured to operate the injector motor in a manner to move the coiled tubing out of the well, thereby adjusting the rate of moving the coiled tubing into or out of the well. 
     
     
         4 . The control system of  claim 1 , wherein the controller is configured to operate one or more counterbalance valves to send fluid flow in a direction needed to move the coiled tubing string within the wellbore. 
     
     
         5 . The control system of  claim 1 , wherein the controller is configured to vary the rate of moving the coiled tubing string within the wellbore when a threshold limit is reached. 
     
     
         6 . The control system of  claim 5 , wherein the threshold limit is a maximum drilling load. 
     
     
         7 . A method of operating a coiled tubing injector for moving a coiled tubing string within a wellbore, the injector including injector motors to power an injector drive mechanism, the injector drive mechanism engaging the coiled tubing to move the coiled tubing string, the method comprising:
 activating a control system and sending a signal to a power source for operating one or more counterbalance valves to send fluid flow to the injector motors to move the coiled tubing string within the wellbore; and   maintaining a substantially constant rate of moving the coiled tubing string within the wellbore.   
     
     
         8 . The method of  claim 7 , further comprising reducing the rate when an upper threshold limit is reached. 
     
     
         9 . The method of  claim 7 , further comprising moving the coiled tubing string to provide a substantially constant rate of drilling. 
     
     
         10 . The method of  claim 9 , further comprising moving the coiled tubing string at a substantially constant rate along a pre-planned well profile. 
     
     
         11 . The method of  claim 7 , further comprising moving the coiled tubing string substantially along a preplanned well profile that is pre-loaded into the system 
     
     
         12 . A coiled tubing unit for moving a coiled tubing string within a wellbore, comprising:
 an injector head having injector motors to power an injector drive mechanism, the injector drive mechanism engaging the coiled tubing string to move the coiled tubing string into or out of the wellbore;   a pump for providing fluid flow to operate the injector motors to power the injector drive mechanism;   a counterbalance valve configured to send the fluid flow from the pump to the injector motors in a direction needed to move the coiled tubing string within the wellbore;   an electro-proportional flow control valve configured to restrict the fluid flow to the injector motors; and   a controller for sending a signal to the pump and the electro-proportional flow control valve for metering the fluid flow that opens the counterbalance valve,   wherein the fluid flow is metered to maintain a substantially constant rate of moving the coiled tubing string within the well.   
     
     
         13 . The coiled tubing unit of  claim 12 , wherein the rate of moving the coiled tubing string within the wellbore is varied when a threshold limit is reached. 
     
     
         14 . The coiled tubing unit of  claim 12 , wherein the rate of moving the coiled tubing string within the wellbore is reduced when an upper threshold limit is reached. 
     
     
         15 . The coiled tubing unit of  claim 14 , further comprising a drill bit at the distal end of the coiled tubing string, wherein the rate of moving the coiled tubing string is reduced when an upper threshold limit of drilling load is met. 
     
     
         16 . The coiled tubing unit of  claim 12 , further comprising a first hydraulic flow line configured to operate the injector motor in a manner to move the coiled tubing into the well, and a second hydraulic flow line configured to operate the injector motor in a manner to move the coiled tubing out of the well. 
     
     
         17 . The coiled tubing unit of  claim 16 , further comprising a fluid line between the first and second hydraulic lines, and a check valve in the fluid line that controls fluid communication between the first and second hydraulic lines, wherein opening the valve in the fluid line adjusts the rate of moving the coiled tubing into or out of the well.