Subsurface Logging Methods 



349 



cut rather than the depth of the well at the time they come to surface. 

 This measurement is accomplished by placing some easily identifiable 

 substance, such as rice or corn in the drill pipe at the derrick floor when 

 making a connection, and measuring the time required to bring the sub- 

 stance around to the shale shaker or return pipe. If regular circulation is 

 being used, it can then be calculated from the pump pressure and volume 

 handled how long the mud requires to go from the derrick floor through 

 the drill pipe to the bit, and this subtracted from the total return time gives 

 the time necessary for the samples to come from the bit to the surface. 



TABLE 18 

 Example of Drilling-Time Form 



Company No 



Location County.. 



Farm. 



State... 



Mud 



Actual time is time spent in drilling. Shut-down time, round trips, changing bit, re- 

 pairs, etc., also condition and type of bit should be noted under "remarks." 



Unless it is known that the hole is in extraordinarily good shape with no 

 washed-out places, it is not satisfactory to calculate the return time from 

 the bit by mud volume and velocity, because some eddying and consequent 

 lowering of the mud velocity takes place in all washed-out places. If it is 

 not possible to determine the sample return time from experimental meth- 

 ods of calculation, a rule of thumb is that under ordinary mud pressure 

 with 7- or 8-inch hole, it will take cuttings about 10 minutes per 1,000 

 feet to return from bottom. 



After the return time of the sample is determined or estimated, each 

 sample should be caught that length of time after the appropriate depth 

 mark on the kelly reaches the rotary table. An easy way to do this is to 

 place on the drilling-time sheet the time each sample should be caught. 

 This is done by adding the return time in minutes to the time at which 

 the given mark is down to the rotary table. This method will eliminate 



