Subsurface Logging Methods 495 



mechanization of sample grinding, weighing, and electrode loading can 

 potentially make an enormous reduction in the most time-consuming opera- 

 tions of the procedure. Second, the elimination of steps leading to precise 

 quantification of absolute values will reduce much of the laborious con- 

 trol of standards, excitation, and energy measurement. In the majority of 

 cases figures on variations in the relative amounts of various elements 

 from sample to sample are as useful as more precise absolute data. It 

 is the pattern formed by changes in percentage with well depth that is 

 more important than the exact amount of each element in each sample. 



COMPOSITE-CUTTINGS-ANALYSIS LOGGING 

 R. J. GILL 



Information obtained simultaneous with the drilling of a wildcat well 

 is of extreme importance, and this knowledge can be acquired at no other 

 time. The establishment of a 24-hour-a-day logging service is based on 

 this premise. 



In order to log a well adequately, the cuttings must be examined and 

 tested for oil and gas concurrent with the drilling, owing to the rapid 

 dissipation of the lighter hydrocarbons that may be brought to the sur- 

 face in the cuttings. Recommendations concerning coring or drill-stem 

 testing may be quickly and accurately made at a time when it is most im- 

 portant. Conversely, much rig time can be saved by eliminating many 

 unnecessary cores and tests. 



It has been proved that cuttings from a well brought to the surface 

 by the mud stream will retain a small fraction of oil or gas, if an oil- 

 or gas-bearing stratum has been penetrated. However, this oil or gas may 

 be present in the cuttings in such minute quantities that it cannot be 

 visually or nasally detected. Mechanical and electrical instruments have 

 been developed to detect and relatively measure obscure oil and gas show- 

 ings in the samples that might otherwise be overlooked. 



This continuous logging process is carried on in a trailer-laboratory, 

 which is located at the well as near to the mud-discharge line as possible. 

 A portion of the mud from the flow line is diverted into the laboratory, 

 where it goes through a miniature shale shaker, which separates the cut- 

 tings from the mud, allowing the mud to return to the pits and providing 

 a continuous flow of samples available for examination. The availability 

 of the cuttings within the laboratory in a steady flow permits examination 

 more frequently and without contamination by previously drilled sedi- 

 ments. 



A cable is run from the laboratory over a sheave near the top of the 

 derrick and down to the swivel. Thus, as the kelly is lowered, the drilling- 

 time mechanism in the laboratory in turn operates and records the time 

 for each foot of hole drilled. The importance of accurate drilling time has 



