relatively homogeneous limestones, but it is supplanted to a great extent by full- 

 diameter methods in vuggy, fractured, cracked, and heterogeneous carbonate 

 rock. 



Full-diameter methods, in general, parallel routine plug analysis, but they 

 have resulted in the development of two different approaches to the problem 

 of handling large sections of core. In the one method fluid saturations are de- 

 termined by vacuum retorting of the section to be analyzed, whereas the second 

 method retorts a crushed sample adjacent to the section to be analyzed. Porosity 

 is determined in the one method by saturation of the section after vacuum re- 

 torting, whereas in the second method a standard Boyle's law porosimeter of 

 sufficient capacity is used. 



The methods differ primarily in the determination of permeability. The 

 one method has introduced the concept of Kmax and Kmin by passing air 

 through the core parallel to its diameter, rotating the core 90 degrees, and making 

 a second reading perpendicular to the first; this process insures that the entire 

 circumference of the specimen has been tested, but it results in two different 

 numerical values for permeability. The second method introduces radial perme- 

 ability; a hole is drilled lengthwise through the section to be tested; the air 

 is impressed against the outer circumference; and the downstream pressure 

 and flow are measured from the inner hole. This method simulates actual well 

 conditions and gives one numerical value which can be used in calculations 

 involving the permeability constant. 



INTERPRETATION OF Core-analysis data for well completion pur- 



CORE-ANALYSIS DATA poses will usually include porosity, perme- 



ability, residual oil saturation, and total water 

 Well Completion saturation. The probable type of production 



is forecast by the fluid saturation figures and 

 the permeability of the rock. The saturation figures, as reported in the analysis, 

 obviously do not reflect the saturation in the reservoir, and the interpretation 

 of these data must be based upon certain assumptions as to the changes in the 

 fluid content from reservoir to laboratory conditions. 



During the coring operations the formation ahead of the drill is partially 

 flushed by mud filtrate, the extent of the flushing action depending upon such 

 factors as the permeability of the formation, excess mud pressure over forma- 

 tion pressure, rate of penetration, and filtrate loss of the coring fluid. The result 

 is a partially flushed core in which an unknown quantity of reservoir fluid has 

 been replaced by an unknown quantity of mud filtrate. 



The partially flushed core is then removed from a high-pressure region in 

 the bottom of the hole to a low-pressure region at the surface, where expansion 



243 



