Plug for well drilling

Abstract

A plug for well drilling comprising a mandrel and members attached on an outer circumferential surface orthogonal to an axial direction of the mandrel. In such a plug for well drilling, at least the mandrel or one of the members is formed from a degradable material and a curvature radius of a bent portion thereof is from 0.5 to 50 mm. Additionally, a well drilling method using the plug for well drilling, the method comprising degrading a part or all of the plug for well drilling after blocking a borehole.

1 . A plug for well drilling comprising: a mandrel and members attached on an outer circumferential surface orthogonal to an axial direction of the mandrel; at least the mandrel or one of the members being formed from a degradable material; and a curvature radius of a bent portion thereof being from 0.5 to 50 mm. 
     
     
         2 . The plug for well drilling according to  claim 1 , wherein the members attached on the outer circumferential surface orthogonal to the axial direction of the mandrel comprise at least one member selected from the group consisting of a slip, a wedge, a pair of ring-shaped fixing members, and a diametrically expandable circular rubber member. 
     
     
         3 . The plug for well drilling according to  claim 2 , wherein the pair of ring-shaped fixing members is capable of fixing the diametrically expandable circular rubber member attached on the outer circumferential surface orthogonal to the axial direction of the mandrel in a compressed state. 
     
     
         4 . The plug for well drilling according to  claim 2 , wherein at least one combination of the slip and the wedge is disposed between the pair of ring-shaped fixing members. 
     
     
         5 . The plug for well drilling according to  claim 1 , wherein the member(s), formed from the degradable material and attached on the outer circumferential surface orthogonal to the mandrel, are formed from a composite material including a degradable material and a metal or an inorganic substance. 
     
     
         6 . The plug for well drilling according to  claim 1 , wherein the mandrel is formed from the degradable material and a curvature radius of a bent portion thereof is from 0.5 to 50 mm. 
     
     
         7 . The plug for well drilling according to  claim 6 , wherein the mandrel formed from the degradable material comprises a hollow part along the axial direction. 
     
     
         8 . The plug for well drilling according to  claim 6 , wherein the mandrel formed from the degradable material and the member(s) attached on the outer circumferential surface orthogonal to the axial direction of the mandrel formed from the degradable material are integrally formed. 
     
     
         9 . The plug for well drilling according to  claim 8 , being integrally formed via integral molding. 
     
     
         10 . The plug for well drilling according to  claim 8 , being integrally formed via machining. 
     
     
         11 . The plug for well drilling according to  claim 1 , wherein the bent portion is at least one selected from the group consisting of a convex part, a stepped part, a flange, a groove, a thread, and a screw bottom. 
     
     
         12 . The plug for well drilling according to  claim 11 , wherein the bent portion further comprises a tapered part, a height of the tapered part being 1 mm or greater. 
     
     
         13 . The plug for well drilling according to  claim 1 , wherein the degradable material is an aliphatic polyester. 
     
     
         14 . The plug for well drilling according to  claim 13 , wherein the aliphatic polyester is polyglycolic acid. 
     
     
         15 . The plug for well drilling according to  claim 14 , wherein the polyglycolic acid has a weight average molecular weight from 180000 to 300000, and a melt viscosity measured at a temperature of 270° C. and a shear rate of 122 sec −1  from 700 to 2000 Pa·s. 
     
     
         16 . The plug for well drilling according to  claim 1 , wherein the degradable material comprises a reinforcing material. 
     
     
         17 . The plug for well drilling according to  claim 1 , wherein the mandrel is formed from the polyglycolic acid. 
     
     
         18 . The plug for well drilling according to  claim 1 , wherein the mandrel formed from the degradable material comprises a ratchet mechanism interlocking part on the outer circumferential surface, a curvature radius of the interlocking part being from 0.5 to 50 mm. 
     
     
         19 . The plug for well drilling according to  claim 1 , wherein the mandrel formed from the degradable material is provided, on the outer circumferential surface, with a male screw structure; one of the pair of ring-shaped fixing members is provided, on an inner circumferential surface thereof, with a female screw structure facing the male screw structure; and the one of the pair of ring-shaped fixing members is fixed in a state disenabling sliding in the axial direction of the mandrel. 
     
     
         20 . A well drilling method using the plug for well drilling according to  claim 1 , the method comprising degrading a part or all of the plug for well drilling after blocking a borehole. 
     
     
         21 . The plug for well drilling according to  claim 2 , wherein the one of the pair of ring-shaped fixing members is fixed in a state disenabling sliding in the axial direction of the mandrel. 
     
     
         22 . A plug for well drilling comprising: a mandrel and members attached on an outer circumferential surface orthogonal to an axial direction of the mandrel; at least the mandrel or one of the members being formed from a degradable material; and a curvature radius of a bent portion thereof being from 0.5 to 50 mm, wherein one of the members is the pair of ring-shaped fixing members formed from the degradable material; and the one of the pair of ring-shaped fixing members is integrally formed with the mandrel and is fixed in a state disenabling sliding in the axial direction of the mandrel.