System and method for casing milling

1. A method for milling an opening into a tubular positioned in a well bore with coiled tubing, comprising:

utilizing a string of coiled tubing;

utilizing a milling tool mounted on said string of coiled tubing;

utilizing an injector motor operable to control an injector for lowering and raising said string of coiled tubing into and out of said well bore;

utilizing an encoder which produces pulses indicative of movement of said string of coiled tubing of coiled tubing into and out of said well bore;

utilizing a tension sensor for said coiled tubing for use in determining a weight on said milling tool during milling; and

utilizing a controller programmed for controlling said injector motor, said controller being operably connected to said tension sensor and said encoder, said controller being programmed to control said injector motor so that said encoder produces less than a predetermined maximum number of pulses for a given time interval, wherein said controller is programmed to control said injector motor to maintain said selected weight unless said encoder produces more than said predetermined maximum number of pulses for said given time period whereupon said controller operates said injector motor to limit or stop lowering of said coiled tubing into said well bore.

2. The method of claim 1 , wherein said controller is programmed to operate said injector motor to stop lowering said coiled tubing for a remainder of said given time interval if said predetermined number of pulses is exceeded and to resume lowering said coiled tubing after said given time interval has lapsed.

3. The method of claim 1 , wherein said controller is operable for calculating a weight on said milling tool based on said tension sensor, a depth of said milling tool, a weight of drilling fluid, and a weight of said coiled tubing.

4. The method of claim 1 , further comprising utilizing a drilling fluid sensor whereby said controller is further programmed to detect out of range values for at least one of drilling fluid flow rate and drilling fluid pressure which indicate a problem with said milling, and wherein said controller is operable for controlling movement of said coiled tubing in response to said out of range values.

5. A coiled tubing milling system for use in milling an opening into a tubular positioned in a well bore, comprising:

a string of coiled tubing;

a milling tool mounted on said string of coiled tubing;

an injector motor operable to control an injector for lowering and raising said string of coiled tubing into and out of said well bore;

an encoder which produces an electronic signal indicative of movement of said string of coiled tubing of coiled tubing into and out of said well bore;

a tension sensor for said coiled tubing for use in determining a weight on said milling tool during milling;

a controller programmed for controlling said injector motor and being operably connected to said tension sensor and said encoder; and

an interface for inputting a selected weight on said milling tool and a maximum rate of movement of said string of coiled tubing, whereby said controller is programmed to maintain said selected weight on said milling tool unless said maximum rate of movement of said string of coiled tubing is exceeded whereupon said controller operates said injector motor to limit or stop lowering of said coiled tubing into said well bore.

6. The system of claim 5 , wherein said encoder produces a predetermined number of pulses for a given movement of said coiled tubing, said controller being programmed to operate said injector motor to limit lowering of said coiled tubing so that said encoder produces less than a predetermined number of pulses for a given time interval.

7. The system of claim 6 , wherein said controller is programmed to operate said injector motor to stop lowering said coiled tubing for a remainder of said given time interval if said predetermined number of pulses is exceeded and to resume lowering said coiled tubing after said given time interval has lapsed.

8. The system of claim 5 , further comprising a drilling fluid sensor whereby said controller is further programmed to detect out of range values for at least one of drilling fluid flow rate and drilling fluid pressure which indicate a problem with said milling.

9. The system of claim 5 , wherein said controller is operable for calculating a weight on said milling tool based on said tension sensor, a depth of said milling tool, a weight of drilling fluid, and a weight of said coiled tubing.

10. A coiled tubing milling system for use in milling an opening into a tubular positioned in a well bore, comprising:

a coiled tubing injector;

a control/monitoring system operatively connected to said coiled tubing injector, said control/monitoring system, once set to a desired rate of penetration of a milling tool into said tubular, controls an advance of said coiled tubing injector to lower coiled tubing into said well bore, such that said desired rate of penetration stays within a desired range, said control/monitoring system comprising a programmable controller for monitoring pulses generated by a depth encoder whereby said programmable controller counts said pulses per a desired time period to monitor said desired rate of penetration;

an electric motor operatively connected to said coiled tubing injector and said programmable controller to rotate and advance said coiled tubing injector at said desired rate;

said programmable controller being programmed to operate said electric motor to stop lowering said coiled tubing for a remainder of said desired time period if said desired range of said rate of penetration is exceeded and to resume lowering said coiled tubing after said given time interval has lapsed.