cuttings into the stream of drilling mud. Some oil also joins the mud stream 

 when the fractured formation surface is exposed by the bit action. 



When the cuttings reach the surface, they are therefore in a general water- 

 flooded condition. The cuttings do not contain amounts of oil and gas that 

 are quantitatively indicative of the amount of oil and gas that may be present 

 in the formation. The cuttings are in about the same condition, as far as 

 their fluid content is concerned, as a core when it reaches the surface, except 

 for being slightly more water flooded. 



Figure 17-5. Automatic recording gas detector. 



CONCLUSIONS 



The following conclusions are borne out by 

 experience : 



The amounts of oil and gas in either the drilling mud or the cuttings 



are a qualitative indication of oil and gas in the formation. 



Except under unusual conditions, reliable shows are obtained in both 



drilling mud and cuttings. 



Conditions allowing large shows of oil and gas are those that contribute 



to a minimum amount of loss of oil and gas from the drilled formation 



by water-flooding action. These are (a) high drilling rate; (b) medium 



to low formation permeability; (c) low pressure differential between the 



mud column and formation; and (d) mud of low filtration rate. 



364 



