System and method for monitoring and controlling snubbing slips

Abstract

A system and method for monitoring and controlling a snubbing unit having traveling slips and stationary slips are provided. Position sensors are associated with the slips for directly or indirectly detecting opened and closed positions of the slips, including detecting a rotational position of a crankshaft that drives the slips into engagement with a pipe. Load sensors are associated with the slips for detecting load status of the slips. A control system receives input signals from the sensors, and confirms that either the traveling slips or the stationary slips are loaded before releasing or allowing the release the opposing set of slips, when transferring the pipe string load from the one set of slips to the other set of slips.

What is claimed is: 
     
         1 . A system for monitoring and controlling a snubbing unit for snubbing a pipe, the snubbing unit having first and second slips operating in tandem to engage and move the pipe into or out of a well, the system comprising:
 (a) a first actuation sensor associated with the first slip and a second actuation sensor associated with the second slip, wherein the actuation sensors directly or indirectly detect engagement of the associated slip on the pipe; and   (b) a control system operatively connected to the first and second actuation sensors and adapted to receive input signals from the sensors, and configured to execute a method comprising the step of confirming that either the first or second s slip (the “unloaded slip”) has engaged the pipe, before fully releasing, or allowing the full release of the other one of the slips (the “loaded slip”), when transferring the pipe load from the loaded slip to the unloaded slip.   
     
     
         2 . The system of  claim 1  wherein the method comprises the further step of confirming that the loaded slip has fully released the pipe and has become unloaded. 
     
     
         3 . The system of  claim 1 , wherein an actuation sensor comprises a position sensor for detecting a position of the associated slip. 
     
     
         4 . The system of  claim 1 , wherein the position sensor comprises a flow meter for measuring a volume of hydraulic fluid flowing into or out of a hydraulic cylinder which actuates the associated slip. 
     
     
         5 . The system of  claim 1  wherein the position sensor directly or indirectly detects the position of a moving part of the associated slip or a moving part of a component which actuates the associated slip, which is indicative of the position of the associated slip. 
     
     
         6 . The system of  claim 5  wherein the position sensor directly or indirectly detects the position of a hydraulic cylinder rod which actuates a slip of the associated slip. 
     
     
         7 . The system of  claim 6  wherein the position sensor directly or indirectly detects a rotational position of a crankshaft that is driven by the hydraulic cylinder rod and that drives the slip into engagement with the pipe. 
     
     
         8 . The system of  claim 7  wherein the position sensor comprises a cam rotated by the crankshaft, a linear cam follower that translates rotational movement of the cam into linear movement, and a linear differential transformer for measuring linear movement of the cam follower. 
     
     
         9 . The system of  claim 1 , wherein any one of the actuation sensors comprises a load sensor for detecting a load on the associated slip. 
     
     
         10 . The system of  claim 9 , wherein the load sensor comprises an air bladder, a hydraulic bladder, an electronic load cell, a hydraulic load cell, or a strain gauge. 
     
     
         11 . The system of  claim 10 , wherein the load sensor comprises a pressure transducer. 
     
     
         12 . The system of  claim 1  wherein any one of the actuation sensors comprises both a position sensor for detecting a position of the associated slip and a load sensor for detecting a load on the associated slip. 
     
     
         13 . The system of  claim 1  wherein the control system further comprises a component which permits or blocks actuation of one of the slips depending on the status of the other slip. 
     
     
         14 . A method of running a pipe into or out of a well with a snubbing unit for snubbing a pipe, the snubbing unit having a first slip and a second slip operating in a sequential manner to engage and move the pipe into or out of the well, the method comprising the steps of:
 (a) engaging the pipe with the first slip and moving the second slip to a first position;   (b) engaging the pipe with the second slip;   (c) confirming with a position sensor or a load sensor, or both a position sensor and a load sensor, that the second slip has adequately engaged the pipe before completely releasing the first slip; and   (d) moving the second slip to a second position to move pipe either into or out of the well.   
     
     
         15 . The method of  claim 14  wherein the confirmation step comprises the step of determining whether or not the second slip has reached a closed position engaging the pipe, or determining whether or not the second slip is bearing a substantial load, or both. 
     
     
         16 . The method of  claim 15  wherein a control system prevents complete release of the first slip unless it is confirmed that the slip has adequately engaged the pipe. 
     
     
         17 . The method of  claim 14  wherein the confirmation step comprises the step of directly or indirectly measuring the rotational position of the crankshaft that drives the second slip into engagement with the pipe.