| Porosity, permeability, and resistance measurements were made on 248 carbonate reservoir rock samples in order to develop an equation describing the relationship between formation resistivity factor and porosity. The specimens, ranging from Mississipian to Tertiary in age, represented formations from Canada, Indonesia, and the United States.;Regression analyses were run to determine the "best fit" equations for three combinations of data: (1) permeability (k)--porosity (;Patch cements, pocket porosity, lamella, and fractures were found to be the most frequent causes of deviation from the FF--porosity best fit line. Seventy-six specimens contained one or more of these features sufficiently effective to cause large variations in the collective resistivity data. Fractures were found to yield reduced resistivity values while the diagenetic features produced elevated values of resistivity.;Data from the 76 deviate samples were removed from the collective data base and regression analyses were run on the remaining data of 172 specimens. This effort yielded the above best fit equation with the following statistical parameters: standard deviation, 0.948; variance, 0.899; and standard error of estimate, 0.08. Calculations showed maximum errors in water saturation values varied 5.5 percent absolute (8.1 to 13.6%) down to zero at about 75 percent water. The newly derived carbonate equation yielded the higher value and the absolute magnitude of the error is also a function of water resistivity (R;Petrographic image and analyses were performed on 108 thin sections. Standard procedures and techniques currently used for sandstone image analyses were found to be inadequate for study of carbonate rock pores smaller in area than 25 square microns. Adequate study of pore configuration in carbonate reservoir rocks must permit quantification of pores at least as small as 0.6 microns in diameter. |
