Activation device for use in a downhole well

Abstract

An activation device for use in a downhole well for activation of a downhole tool in the well. The downhole tool has a seat adapted to engage the activation device. The activation device can travel through a borehole of the downhole well to reach the seat. The activation device has an outer layer and a core. The material of the outer layer resists erosion by drilling fluid when the activation device is in the borehole. The material of the core is eroded by drilling fluid when the activation device is engaged in the seat. The activation device is then able to pass through the seat. There is also described a method of operating a downhole tool having a seat for engaging an activation device. The method includes the step of eroding at least a portion of the activation device with drilling fluid until it can pass through the seat.

1 . An activation device for use in a downhole well for activation of a downhole tool in the well, the downhole tool having a seat adapted to engage the activation device whereby engagement of the activation device in the seat changes the activation status of the downhole tool, the activation device being adapted for passage through the borehole of the well and being adapted to engage the seat of the downhole tool in the well to change the activation status of the downhole tool, the activation device comprising an outer layer and a core housed within the outer layer, and wherein the material of the outer layer is adapted to resist erosion during passage of the activation device through the borehole of the well in normal operating conditions, and wherein the material of the outer layer and the core are adapted to be eroded by drilling fluid when the activation device is engaged in the seat in the downhole tool, whereby the drilling fluid erodes the seated activation device such that the activation device is able to pass through the seat. 
     
     
         2 . An activation device according to  claim 1  wherein the activation device comprises a substantially spherical ball. 
     
     
         3 . An activation device according to  claim 1  wherein the core has a compressive strength from 10 to 140 MPa. 
     
     
         4 . An activation device according to  claim 1  wherein the material of the outer layer is selected from the group consisting of cement, concrete, epoxy resin, ceramic, MOLYKOTE®, ester, flourosilicone, mineral oil, polyalkyleneglycol; polyalphaolephin, perflouropolyether, silicone, and siloxane grease. 
     
     
         5 . An activation device according to  claim 1  wherein the material of the core is selected from the group consisting of wax, salt, and sand. 
     
     
         6 . An activation device according to  claim 1  wherein the activation device is adapted to be eroded by the flow of drilling fluid past the seated activation device. 
     
     
         7 . An activation device according to  claim 1  wherein the core comprises a material adapted to change state from solid to liquid when exposed to normal temperatures in the environment of the seat. 
     
     
         8 . An activation device according to  claim 1  wherein the core comprises a material that is more susceptible to erosion than the material of the outer layer. 
     
     
         9 . An activation device according to  claim 1  wherein the material of the outer layer is epoxy resin, the material of the core is a salt and wherein the core has a compressive strength from 10 to 140 MPa. 
     
     
         10 . A method of operating a downhole tool in a borehole of an oil or gas well, the downhole tool having a seat for engaging an activation device, the method comprising the steps of:
 providing an activation device adapted to pass through at least a part of the borehole and engage the seat, the activation device comprising a core and an outer layer of material housing the core;   transporting the activation device in a flow of drilling fluid through the borehole from an insertion point in the borehole to the seat of the downhole tool, whereby the activation device engages in the seat of the downhole tool;   changing the state of activation of the downhole tool when the activation device engages with the seat, and   eroding at least a portion of the activation device with drilling fluid until the activation device can pass through the seat.   
     
     
         11 . A method according to  claim 10  wherein the activation device is eroded by flowing the drilling fluid past the activation device when the activation device is in the seat of the downhole tool. 
     
     
         12 . A method according to  claim 10  wherein the core comprises a material that is more susceptible to erosion than the material of the outer layer, whereby erosion of the outer layer to expose the core takes more time than the subsequent erosion of the core. 
     
     
         13 . A method according to  claim 10  wherein the activation device is eroded after the step of changing the activation status of the downhole tool. 
     
     
         14 . A method according to  claim 10  wherein the eroded activation device passes through the seat and is washed away from the downhole tool by the drilling fluid. 
     
     
         15 . A method according to  claim 10  wherein the activation device erodes over a period of between  10  seconds and  20  minutes when located on the seat member. 
     
     
         16 . A method according to  claim 10  wherein the velocity of the drilling fluid is between 5 and 45 metres per second. 
     
     
         17 . A method according to  claim 10  wherein the activation device is eroded by particles of solids transported in the drilling fluid. 
     
     
         18 . A method according to  claim 10  wherein the activation status of the downhole tool is changed a second time by a second activation device, the method comprising the further steps of:
 providing a second activation device adapted to pass through at least a part of the borehole and engage the seat, the second activation device comprising a core and an outer layer of material housing the core; 
 transporting the second activation device in the flow of drilling fluid through the borehole to the seat of the downhole tool, whereby the second activation device engages in the seat of the downhole tool; 
 changing the state of activation of the downhole tool when the second activation device engages with the seat, and 
 eroding at least a portion of the second activation device with drilling fluid until the second activation device can pass through the seat. 
 
     
     
         19 . An activation device for use in a downhole well for activation of a downhole tool in the well, the downhole tool having a seat adapted to engage the activation device whereby engagement of the activation device in the seat changes the activation status of the downhole tool, the activation device being adapted for passage through the borehole of the well and being adapted to engage the seat of the downhole tool in the well to change the activation status of the downhole tool, the activation device comprising an outer layer and a core housed within the outer layer, wherein the core has a compressive strength from 10 to 140 MPa and wherein the material of the outer layer is adapted to resist erosion during passage of the activation device through the borehole of the well in normal operating conditions, and wherein the material of the outer layer and the core are adapted to be eroded by drilling fluid when the activation device is engaged in the seat in the downhole tool, whereby the drilling fluid erodes the seated activation device such that the activation device is able to pass through the seat. 
     
     
         20 . An activation device according to  claim 19 , wherein the material of the outer layer is selected from the group consisting of cement, concrete, epoxy resin, ceramic, MOLYKOTE®, ester, flourosilicone, mineral oil, polyalkyleneglycol; polyalphaolephin, perflouropolyether, silicone, and siloxane grease. 
     
     
         21 . An activation device according to  claim 19 , wherein the material of the core is selected from the group consisting of wax, salt, and sand.