Mud motor pressure absorption tools

Abstract

A pressure absorbing tool is attached to a workover motor in a milling assembly. The tool includes an upper housing portion that is secured to a drilling string, and a lower mandrel portion that is secured to the workover motor and is moveable axially, but not rotationally with respect to the upper housing portion between an axially compressed position and an axially extended position. Longitudinal grooves are inscribed on the lower mandrel portion, and a plurality of guide members are associated with the upper housing and disposed within the grooves. The axially retracting design uses pressure acting across two pistons to retract as the motor stalls. The Belleville washers bias the tool to the extended position once the motor has returned to operating conditions.

1 . A pressure absorbing tool for attachment to a workover motor in a milling assembly, the tool comprising: 
 an upper housing portion that is secured to a drilling string;    an lower mandrel portion that is secured to a mud motor;    the lower mandrel portion being moveable axially, but not rotationally with respect to the upper housing portion between an axially compressed position and an axially extended position; and    a compressive spring member to urge the lower mandrel portion toward the axially extended position.    
   
   
       2 . The tool of  claim 1  further comprising: 
 a longitudinal groove inscribed on the lower mandrel portion; and    a guide member associated with the upper housing and slidingly disposed within the longitudinal groove.    
   
   
       3 . The tool of  claim 2  wherein the guide member presents a rounded inner contact surface contacting the groove.  
   
   
       4 . The tool of  claim 3  wherein the inner contact surface is hemispherical.  
   
   
       5 . The tool of  claim 2  wherein there are multiple longitudinal grooves and multiple guide members.  
   
   
       6 . The tool of  claim 1  wherein the compressive spring member comprises a Belleville washer.  
   
   
       7 . The tool of  claim 6  wherein there are a plurality of Belleville washers, and wherein the tool further comprises a guide sleeve disposed radially within the Belleville washers.  
   
   
       8 . The tool of  claim 2  wherein there is a plurality of longitudinal grooves inscribed on the lower mandrel portion.  
   
   
       9 . The tool of  claim 8  wherein there are four longitudinal grooves inscribed on the lower mandrel portion.  
   
   
       10 . A milling system comprising: 
 a drill string;    a workover motor for operating a milling tool bit in response to flow of drilling fluid through the drill string;    a pressure absorbing tool incorporated within the drill string above the workover motor for absorption of pressure spikes from the workover motor; the pressure absorbing tool comprising: 
 an upper housing portion that is secured to the drill string;  
 an lower mandrel portion that is secured to the workover motor;  
 the lower mandrel portion being moveable axially, but not rotationally, with respect to the upper housing portion between an axially compressed position and an axially extended position;  
 at least one longitudinal groove inscribed on the lower mandrel portion;  
 at least one guide member associated with the upper housing and slidingly disposed within the at least one longitudinal groove; and  
 a compressive spring mechanism to urge the lower mandrel portion toward the axially extended position.  
   
   
   
       11 . The drilling system of  claim 10  wherein the drilling string comprises coiled tubing.  
   
   
       12 . The drilling system of  claim 10  wherein the compressive spring mechanism comprises at least one Belleville washer.  
   
   
       13 . The drilling system of  claim 10  wherein the compressive spring mechanism comprises a fluid spring.  
   
   
       14 . The drilling system of  claim 10  wherein the compressive spring mechanism comprises a coil spring.  
   
   
       15 . The drilling system of  claim 10  wherein the guide member presents a rounded inner contact surface contacting the at least one longitudinal groove.  
   
   
       16 . The drilling system of  claim 10  wherein there are multiple longitudinal grooves.  
   
   
       17 . A method of absorbing pressure spikes associated with milling operations by a coiled tubing-run milling system, the method comprising the steps of: 
 incorporating a pressure absorbing tool into the milling system above a workover motor;    operating a milling tool of the milling system by flowing drilling fluid through the workover motor; and    absorbing axial forces resulting from motor pressure spikes by moving an lower mandrel portion of the pressure absorbing tool axially, but not rotationally, with respect to an upper housing portion of the pressure absorbing tool, the lower mandrel further being axially guided by an interface of sliding of guide members within longitudinal grooves.    
   
   
       18 . The method of  claim 17  further comprising the step of urging the pressure absorbing tool to an axially extended position with a compressive spring member and pistons.