A downhole-started self-locking casing centralizer

Abstract

The invention relates to a downhole-started self-locking casing centralizer, comprising a connecting part ( 1 ) and a connecting part ( 2 ) on both ends, a central supporting part being arranged between the connecting part ( 1 ) and the connecting part ( 2 ), and characterized in that the central supporting part comprises a hollow coupler, and at least three N-stage piston self-locking support devices extending by stages under pressure are evenly distributed along the circumference of the coupler, N≧2. The invention has the following advantages: 1. a threaded integral structure is adopted; 2. a downhole-started self-locking support structure is adopted; and 3. a circular arc support cap helps ensure large support force and reduce damage to borehole walls.

What is claimed is: 
     
         1 . A downhole-started self-locking casing centralizer, comprising a connecting part ( 1 ) and a connecting part ( 2 ) on both ends, a central supporting part ( 3 ) being arranged between the connecting part ( 1 ) and the connecting part ( 2 ), and characterized in that the central supporting part ( 3 ) comprises a hollow coupler ( 5 ), and at least three N-stage piston self-locking support devices extending by stages under pressure are evenly distributed along the circumference of the coupler ( 5 ), N≧2;
 each N-stage piston self-locking support device comprises a support shell ( 4 - 1 ) fixed to the coupler ( 5 ) and a N-stage support consisting of a first stage support through an N th  stage support, the first stage support and the support shell ( 4 - 1 ) are in a sliding fit, the first stage support through the N th  stage support are in a sliding fit successively by two adjacent stages so that the N-stage support can extend by stages under pressure from the N stage support, a supporting part ( 4 - 5 ) for contacting with wall supports is arranged at the end where the N th  stage support goes against the support shell ( 4 - 1 ), fracture rings are formed at the bottoms of the first stage support through the N th  stage support, and the fracture rings allow starting pressure of the first stage support through the N th  stage support to drop by stages. 
 
     
     
         2 . The downhole-started self-locking casing centralizer of  claim 1 , characterized in that the first stage support of each of the N-stage piston self-locking support device is nested in the support shell ( 4 - 1 ), and the N th  stage support through the first stage support are successively nested by two adjacent stages, wherein, a k th  stage support is nested in a k−1 st  stage support, k=1, . . . , N. 
     
     
         3 . A downhole-started self-locking casing centralizer of  claim 2 , characterized in that the fracture ring of the current support and the inner wall of an adjacent support are in an interference fit, and the fracture ring of the first stage support and the inner wall of the support shell ( 4 - 1 ) are in an interference fit. 
     
     
         4 . A downhole-started self-locking casing centralizer of  claim 2 , characterized in that in each of the N-stage piston self-locking support device, at least one N th  stage ratchet-shaped locating slot is arranged on the outer circumferential surface of the N th  stage support, at least one ratchet-shaped locating slot is arranged respectively on the outer circumferential surface of the N−1 st  stage support through the first stage support, and a C-shaped locating self-locking ring is arranged respectively on the inner wall of the N−1 st  stage support through the first stage support, wherein, at least one j th  stage ratchet-shaped locating slot is arranged on the outer circumferential surface of the j th  stage support, and one j+1 st  stage C-shaped locating self-locking ring is arranged on the inner wall thereof, j=1, . . . , N−1, the N stage ratchet-shaped locating slot is fitted with the N−1 st  stage C-shaped locating self-locking ring, the j th  stage ratchet-shaped locating slot is fitted with the j th  stage C-shaped locating self-locking ring, and the first stage locating self-locking ring is arranged on the inner wall of the support shell ( 4 - 1 ). 
     
     
         5 . A downhole-started self-locking casing centralizer of  claim 2 , characterized in that in each of the N-stage piston self-locking support device, two adjacent supports as well as the first stage support and the support shell ( 4 - 1 ) are sealed respectively by a sealing ring. 
     
     
         6 . A downhole-started self-locking casing centralizer of  claim 1 , characterized in that both the connecting part ( 1 ) and the connecting part ( 2 ) are of casing-connected thread structures. 
     
     
         7 . A downhole-started self-locking casing centralizer of  claim 1 , characterized in that the contact part between the supporting part ( 4 - 5 ) and the wall supports is a half-arc support contact cap ( 4 - 5 - 1 ).