Core barrel and core drilling systems and methods

Abstract

Example embodiments provide downhole apparatus and methods for wireline core drilling. Example apparatus comprises an outer tube having at least one helical groove formed in an outer surface of the outer tube. The apparatus may also comprise an inner tube for collecting a core sample. The inner tube may be received within a bore of the outer tube. The inner tube and the core sample may be retrieved to a surface by a wireline.

1 . Downhole apparatus for wireline core drilling comprising:
 an outer tube having at least one helical groove formed in an outer surface of the outer tube; and   an inner tube for collecting a core sample, the inner tube receivable within a bore of the outer tube, the inner tube and the core sample retrievable to a surface by a wireline.   
     
     
         2 . The apparatus of  claim 1  wherein the outer tube comprises two or more shorter tubes. 
     
     
         3 . The apparatus of  claim 1  wherein the outer tube is at least 2 m long. 
     
     
         4 . The apparatus of  claim 1  wherein the at least one helical groove has a depth that is less than about 0.15 cm. 
     
     
         5 . The apparatus of  claim 1  wherein the at least one helical groove has a width that is less than about 2 cm. 
     
     
         6 . The apparatus of  claim 1  wherein the at least one helical groove is formed on an angle in the range of about 10° to about 20°. 
     
     
         7 . The apparatus of  claim 6  wherein the angle is about 15°. 
     
     
         8 . The apparatus of  claim 1  wherein the at least one helical groove makes at least 4 full rotations around the outer tube over an entire length of the outer tube. 
     
     
         9 . The apparatus of  claim 1  wherein the at least one helical groove has a depth that is less than 15% of a wall thickness of the outer tube. 
     
     
         10 . The apparatus of  claim 1  wherein the at least one helical groove is a multi-start helical grove having at least 4 starts. 
     
     
         11 . The apparatus of  claim 2  wherein the outer tube comprises a first shorter tube having a first set of helical grooves and a second shorter tube having a second set of helical grooves, the first and second shorter tubes coupled together. 
     
     
         12 . The apparatus of  claim 11  wherein coupling the first and second shorter tubes together aligns the first set of helical grooves with the second set of helical grooves. 
     
     
         13 . The apparatus of  claim 11  wherein at least one of the first and second shorter tubes comprises a circumferential gap, the circumferential gap allowing for flow of fluid between the first and second sets of helical grooves when the first and second shorter tubes are coupled together. 
     
     
         14 . The apparatus of  claim 11  wherein the first and second shorter tubes are coupled together with a threaded coupling. 
     
     
         15 . The apparatus of  claim 1  wherein an outer diameter of the outer tube is substantially equal to an inner diameter of a drilled hole. 
     
     
         16 . The apparatus of  claim 15  wherein a difference between the outer diameter of the outer tube and the inner diameter of the drilled hole is about 1 mm or less. 
     
     
         17 . The apparatus of  claim 1  wherein the outer tube comprises 4130 alloy steel. 
     
     
         18 . An outer tube for a core barrel for deep wireline core drilling comprising at least one helical groove formed in an outer surface of the outer tube, the outer tube comprising a bore to receive an inner tube for collecting a core sample, the inner tube and the core sample retrievable to a surface by a wireline. 
     
     
         19 .- 21 . (canceled)