Well Servicing Vehicle With Method for Detecting Well String Snags

Abstract

Example well servicing vehicles for removing and installing well strings (e.g., sucker rods and tubing) within wellbores provides a method for determining and logging snag points within the wellbore. In some examples, snag points are determined based on a predetermined change in cable tension, crown load strain and/or hydraulic pressure. The predetermined change is adjusted based on the current length of the well string at the time the snag occurs.

1 . A workover method for handling a well string the extends into a wellbore, wherein the method involves the use of an elevator carried by a mast and connected to the well string, the workover method comprising:
 supplying oil at a pressure that varies;   using the pressure as means for raising the elevator connected to the well string;   monitoring an elevation of the elevator, wherein the elevation increases while raising the elevator;   monitoring the pressure while raising the elevator;   if the pressure experiences a certain spike in pressure, a controller noting the elevation at which the certain spike occurred; and   determining a location within the wellbore based on the elevation at which the certain spike occurred.   
     
     
         2 . A workover method for handling a well string through the use of an elevator carried by a mast, the workover method comprising:
 determining a first anticipated maximum load of the well string;   during a first period, shortening the well string to create a shorter well string;   determining a second anticipated maximum load of the shorter well string;   during a second period, shortening the shorter well string to create an even shorter well string;   establishing a first oil pressure limit based on the first anticipated maximum load of the well string;   establishing a second oil pressure limit based on the second anticipated maximum load of the shorter well string;   during the first and second period, discharging oil at a discharge pressure that varies;   limiting the discharge pressure to the first oil pressure limit during the first period; and   limiting the discharge pressure to the second oil pressure limit during the second period, wherein the first oil pressure limit is greater than the second oil pressure limit, and the second oil pressure limit is less than a minimum discharge pressure necessary to handle the first anticipated maximum load of the well string.   
     
     
         3 . A workover method for handling a well string that extends into a wellbore, wherein the workover method involves the use of an elevator carried by a trolley that travels along a mast, the workover method comprising:
 the elevator suspending the well string while the well string extends into the wellbore;   a sensor determining whether the elevator is descending;   monitoring at least one of a cable tension, a crown load strain and a hydraulic pressure;   identifying a notable decrease in at least one of the cable tension, the crown load strain and the hydraulic pressure; and   determining a stack-out condition in the event of the notable decrease occurring while the elevator is descending.