admirably to specific and special tests, such as connate water, relative perme- 

 ability, acid solubility, and flood pot, among others, from which productivity, 

 secondary recovery, and well treatment can be deduced. 



SAMPLING OF CORES The core should be sampled with the thought 



in mind of obtaining representative data and 

 true net pay thickness. The general custom in the industry is to sample every 

 foot of cored section, and more often if a visible change in characteristics occurs. 

 The samples are marked or labeled as to interval or depth from which obtained, 

 and preserved for transportation to the laboratory. 



The two most commonly used methods of preservation of core samples 

 consist of canning or sealing in plastic bags and quick freezing with dry ice. 

 Either method will preserve the fluid content of the sample, and it is obvious 

 that the rock characteristics will not be changed when sealed in air-tight 

 containers. The freezing process has been subjected to criticism by the claim 

 that some of the basic characteristics of the core, e.g., porosity and permeability, 

 are altered during the freezing and thawing cycle. 



TYPES OF Core analysis is grouped into three categories: 



CORE ANALYSIS (1) small plug or routine analysis; (2) full 



diameter or special analysis; and (3) all other 

 general and specific tests not of a routine nature. 



Routine or plug analysis consists of determinations for porosity, perme- 

 ability, and fluid saturation utilizing 3^ -inch or 1-inch plugs drilled from the 

 core. This method has proved satisfactory for homogeneous material such as 

 unfractured sandstones and limestones but is limited to analysis of matrix 

 characteristics due to inability to incorporate cracks and fractures in the 

 specimen. 



Full diameter analysis was developed to overcome the deficiences of plug 

 analysis. This technique analyzes the entire core, cut or broken to convenient 

 lengths. The influence of vugs, cracks, and fractures on the basic characteristics 

 of the rock is thus measured, as both matrix and fracture porosity and perme- 

 ability are included in the test specimen. 



General core analysis consists of all special tests that do not involve routine 

 porosity, permeability, and fluid saturations. This category includes capillary 

 pressure curves, connate water determinations, flooding tests, acid solubilities, 

 pore-size distribution, grain-size distribution, and similar and related analyses. 



230 



