318 Subsurface Geologic Methods 



grams. The water-permeability curve will show the portions of the sand 

 body that will most readily take water in water flooding and will also 

 show where water production will first occur if water encroachment takes 

 place. 



The plotting of the impermeable barriers enables the operator to 

 make use of natural shutoffs for the control of high gas-oil-ratio and 

 bottom-water production. 



The residual-oil plot shows the oil found in the core and is expressed 

 in percentage of the pore space. Where gas-condensate or distillate is 

 measured, the residual condensate is plotted as oil type (figs. 122 and 

 126). 



The production index is based on a relationship between the analyzed 

 physical characteristics of the cores and is an expression of the type of 

 production to be expected. 



The gravity of the residual oil as determined by core analysis or 

 drill-stem tests is presented on the core-log whenever the formation is 

 considered oil-productive. 



Summary of Applications of Core Analysis 

 Exploration 



The analyses of representative core samples and the intelligent inter- 

 pretation of the data are aids in the evaluation of the commercial possi- 

 bilities of wildcat wells, edge wells, and field extensions. Core analyses 

 together with electric and mechanical well logging make possible corre- 

 lation work. 



The determination of the oil gravity and of the productive capacity of 

 oil-bearing formations minimizes the possibility of completing a dry hole 

 or missing a productive formation. 



Where wells are drilled to total depth without coring, an electric log 

 can be run, and the zones that exhibit possibilities of hydrocarbon satura- 

 tion may be cored with any one of a number of sidewall-coring devices. 

 The analysis of sidewall samples is a highly specialized technique, and 

 the interpretation of the core data requires an extensive knowledge of the 

 physical characteristics of each formation as represented by full-diameter- 

 core data. 



Exploitation 



Core-analysis data may be used with reservoir-fluid-analysis data to 

 predict the productive history of a formation and thus predetermine the 

 required capacity of the field equipment throughout the producing life 

 of the reservoir. Selection of the most effective well-spacing pattern may 

 be guided by core analysis. 



Evaluation of oil and gas reservoirs can be made by the use of core 

 data, and the probable recoveries can be calculated. 



Core-analysis data are essential for reservoir-performance predictions 



