Mitigating Swab and Surge Piston Effects in Wellbores

Abstract

A method of mitigating undesired pressure variations in a wellbore due to movement of a well tool string in a well can include selectively decreasing and increasing fluid communication between sections of a wellbore on opposite sides of at least one well tool in the well tool string, the fluid communication being increased in response to detecting a threshold movement of the well tool string relative to the wellbore. A well tool string can include a well tool connected in the well tool string, and having an enlarged outer dimension relative to adjacent sections of the well tool string, a flow passage extending between the well tool's opposite ends, a sensor, and at least one flow control device which selectively permits and prevents fluid communication between the opposite ends via the flow passage, in response to an output of the sensor indicative of movement of the well tool string.

What is claimed is: 
     
         1 . A well tool string, comprising:
 at least one well tool connected in the well tool string, the well tool having an outer dimension which is enlarged relative to at least one adjacent section of the well tool string;   a flow passage extending between opposite ends of the well tool;   a sensor; and   at least one flow control device configured to selectively increase and decrease fluid communication between the opposite ends of the well tool via the flow passage, in response to an output of the sensor indicative of movement of the well tool string.   
     
     
         2 . The well tool string of  claim 1 , wherein the sensor senses a pressure differential across the well tool. 
     
     
         3 . The well tool string of  claim 1 , wherein the sensor senses acceleration of the well tool string. 
     
     
         4 . The well tool string of  claim 1 , wherein the flow control device prevents fluid communication between the opposite ends of the well tool in response to at least one of rotation, torque and compression in the well tool string. 
     
     
         5 . The well tool string of  claim 1 , wherein the at least one flow control device comprises multiple flow control devices, actuation of the flow control devices being synchronized, so that the flow control devices open and close together. 
     
     
         6 . The well tool string of  claim 5 , wherein the actuation of the flow control devices is synchronized via telemetry. 
     
     
         7 . The well tool string of  claim 1 , wherein the flow passage is configured for directing drilling fluid to a drill bit. 
     
     
         8 . The well tool string of  claim 1 , wherein the flow passage extends through a drill bit. 
     
     
         9 . The well tool string of  claim 1 , wherein flow through the flow passage is permitted in response to the sensor output being indicative of a predetermined level of acceleration of the well tool string. 
     
     
         10 . The well tool string of  claim 1 , wherein flow through the flow passage is permitted in response to the sensor output being indicative of a predetermined level of pressure differential across the well tool. 
     
     
         11 . A method of mitigating pressure differentials across at least one well tool in a well tool string, the method comprising:
 sensing at least one parameter indicative of pressure differential across the well tool; and   opening at least one flow control device, thereby providing fluid communication between sections of a wellbore on opposite sides of the well tool, the opening being performed when the parameter exceeds a threshold level.   
     
     
         12 . The method of  claim 11 , wherein the parameter comprises acceleration of the well tool string. 
     
     
         13 . The method of  claim 11 , wherein the parameter comprises pressure differential between the wellbore sections. 
     
     
         14 . The method of  claim 11 , wherein the opening further comprises permitting flow through a flow passage extending through the well tool. 
     
     
         15 . The method of  claim 14 , wherein the flow passage is configured for directing drilling fluid to a drill bit. 
     
     
         16 . The method of  claim 14 , wherein the flow passage extends through a drill bit. 
     
     
         17 . The method of  claim 14 , wherein the flow passage extends longitudinally through the well tool string. 
     
     
         18 . The method of  claim 14 , wherein the at least one flow control device comprises multiple flow control devices, and wherein the opening further comprises opening the flow control devices, thereby permitting fluid communication between the flow passage and the wellbore sections. 
     
     
         19 . The method of  claim 18 , further comprising synchronizing the opening of the flow control devices via telemetry. 
     
     
         20 . The method of  claim 19 , further comprising synchronizing closing of the flow control devices via telemetry.