SAMPLES Samples are best taken from the point nearest the drill hole. A bucket of cuttings is caught and care fully washed and then inspected. • A capable rotary driller can tell from the feel Of the drilling tools when a " in formation" has occurred. He measures the point on his grief stem. He will then watch the ditch carefully and take samples. A change in the character of the material is logged. I Oil or gas may also show in the ditch and thus give positive evi dence of their presence. In such a case a test of the sand is justified 1 if the showing is a good one. 1 One danger with the rotary is in mudding-up the beds so that oil or gas does not show at all. Good oil horizons have been passed by in this way.
Careful logs can be kept with the rotary system, but it requires very close inspection to make a good analysis of rotary cuttings.
Core Barrel.—In taking samples in rotary drilling the core barrel provides an excellent method of obtaining good tests of the forma tion. This core barrel is put on
the bottom of the drill pipe, -and is rotated into the forma tion. The core taken from the core-barrel furnishes an excellent sample.
Hydraulic Circulator The Circulator System as used with the cable-tool system calls for the use of heavy mud pumps.
These pumps drive a mixture of clay and water down the casing and up around the outside of the casing to the top of the hole. Con stant circulation is maintained (see Fig. 21, page 66).
This method of drilling varies from the Standard Cable-Tool system in that the casing is kept only a short distance above the tools and that the water drives the cuttings from the hole. How ever, a bailer is employed to get samples as in the Standard Cable Tool systems. The cable tools work through a circulator• head. (See Fig. 21, page 66.)