1084 



EXPLORATION GEOPHYSICS 



the body of the sampler, and the tool is removed from the hole with samples of the 

 formation in the core tubes. 



Another instrument has been designed especially to recover the harder formations. 

 This instrument comprises a diamond core drill, driven by an electric motor, and is 

 guided by a track on which it slides into the cylindrical body of the instrument. Ordi- 

 narily the drill is retracted inside the body. In drilling a core, it extends diagonally 

 downward from the side of the instrument. Before the coring operation, the instrument 

 is anchored in the hole at any desired depth by an anchor arm system, which is released 

 from an initially retracted position by the rotation of the electrical motor. Then, as 

 the cable is slackened, the anchor pushes the instrument against the side of the wall to 

 be cored ; the rotating drill is applied against the formation with a pressure furnished 

 by the weight of the driving motor, and a core is cut. When the drilling of the core 

 is complete, the core is broken off at its root by a percussion motion and the drill is 

 retracted from the formation with the core inside it. Provision is made for the removal 



of the core from the drill and for its temporary 

 storage in a core magazine, so that several cores can 

 be taken during one trip in the hole. 



The mechanical sample taker is about 10 feet 

 in length, 5 inches in diameter, and weighs approxi- 

 mately 290 pounds. It can be run in holes from 

 7 inches up to 12 inches in diameter. From three to 

 ten minutes time is required to cut a core, and as 

 many as nine cores per run can be taken within a 

 period of three hours or less, according to the depth 

 and nature of the formations cored. Successful 

 operations have been performed down to 11,000 feet. 





m^ 





m 





f,ZZ~^ 







A- Loaded jnd in Firing Position. 



m 



W 



■Mm 



The cores obtained are ^" in diameter and from 

 2" to 2^" in length. On the average they are 

 appreciably longer than the cores taken by the per- 

 cussion-type sample taker. They are usually suitable 

 for porosity, permeability, and other analyses. The 

 recovery depends on the type of formation and also 

 on the conditions of the well. The average recovery 

 is about 80 per cent and is likely to be improved 

 still more in the near future. 



^ 



S'&ullet fired into For /nation 



Fig. 676. — Schluniberger gun-type 

 sample taker. 1, bullet; 2, retrieving 

 wire; 3, explosive; 4, ignition wire; 

 5, firing cable; 6, removable cap. 



Percussion or Gun Samplers 



The operating principles of the gun-type 

 mechanical side wall sample takers t are 

 illustrated in Figure 676, Part A shows 

 the loaded gun in a well with the essential 

 parts : bullet, fastening wires, powder, and 

 igniting wire. By means of two electrical connections, a current is passed 

 through the igniting wire, which thereupon becomes heated and ignites the 

 explosive. The bullet is propelled into the formation as illustrated in Figure 

 676B. During this process, the bullet bottom cap is forced off so that the 

 mud cake on the wall of the hole, which is collected first, passes through. 

 The bullet is recovered by lifting the gun, which in turn pulls the bullet, 

 with sample, from the formation by the fastening wires. A view of a 



t M. Schlumberger, U. S. Patents 2,055,506, issued Sept. 19, 1936, and 2,119,361, issued 

 May 31, 1938. 



E. G. Leonardon, "Exploring Drill Holes by Sample Taking Bullets," A.I.M.E. Pet. Tech., 

 1939. 



