624 imbt. CARBONATE POROSITY PROBLEMS [Ch. 33 



the reservoir as a result of the action of ground waters on previously 

 existing porosity and permeability. Determination of crystal size, 

 composition, and arrangement should furnish important data regarding 

 the relationship of the porosity to present conditions in the rock and 

 to the sequence of events during the geologic past. 



(2) Standardized techniques of core analysis give dependable values 

 for the simple gross quantities of porosity and permeability. Both 

 vertical and horizontal porosity and permeability values should be 

 determined for purposes of correlating experimental data. 



(3) A technique of impregnating porous carbonates with a plastic 

 known as Catalin has been developed which produces a faithful cast 

 of the original pore space. Briefly, plastic is impregnated under high 

 pressure into samples of reservoir rock that have first been cleaned 

 and dried. Air is evacuated from the pore spaces, and plastic is forced 

 into the openings. The Catalin polymerizes in about 72 hours at 80° C. 

 After polymerization, the specimen is sectioned and placed in hydro- 

 chloric and hydrofluoric acid to digest the carbonates and silicates. 

 The plastic, which is not affected by either acid, remains as a model of 

 the porosity and permeability plus those parts of the original rock not 

 affected by either acid. The resulting mold furnishes a replica of the 

 connected pore spaces, something that can be handled and studied 

 for the geological story it tells. The plastic-model approach promises 

 to be a useful tool in its application to specific reservoir problems and 

 studies when a qualitative answer is desired. It is also possible that 

 quantitative techniques could be developed in the plastic-model 

 method. 



The photographs in Figs. 1 through 7 were made of actual plastic 

 models of carbonate rocks collected in west Texas, Oklahoma, and 

 Kansas; they clearly illustrate the effectiveness of plastic impregna- 

 tion as an aid in telling a geologic story. In the interpretation of these 

 photographs, it is important to remember that the dark areas represent 

 rock mass which was not porous or permeable and therefore did not 

 receive the impregnation of Catalin. The white portion of the picture 

 is Catalin that was forced into the porosity and therefore represents a 

 model of the porosity. 



Figures 1 and 2 are examples of intercrystalline-type porosity. 

 Figure 1 is Devonian dolomite from west Texas which suggests devel- 

 opment of intercrystalline porosity along a fracture. Figure 2 is a 

 model of Arbuckle intercrystalline porosity from Barton County, Kan- 

 sas. This model shows no evidence of fracture-controlled porosity but 

 rather an irregular pattern with constrictions between the larger pores. 



