1962 Paper B

FURTHER STUDIES IN RESISTIVITY EFFECTS OF VARIOUS MUD ADDITIVES

Hamilton M. Johnson* and Robert F. Beyer, Jr.**

*Professor of Geology and Geophysics, Tulane University, New Orleans, La. *Schlumberger Well Surveying Corporation, Houston, Texas.

ABSTRACT

Measurements of the mud resistivity (Rm), mud filtrate resistivity (Rmf) and mudcake resistivity (Rmc) were made for various mud additives under different conditions of temperature and concentration. A mud of Wyoming bentonite (AQUAGEL) suspended in water, into which fifteen percent by volume diesel oil had been emulsified, was used as a reference standard. The additives were tested individually at concentrations from 1000 to 5000 ppm and through temperatures ranging from 80°F to 270°F for each concentration.

Additives checked were sodium tannate (HYDROTAN), modified ferrochrome lignosulfonate (Q-BROXIN), sodium bicarbonate (SMENTOX), sodium tetraphosphate (BARAFOS), mineral lignin (CARBONOX), powdered organic starch (IMPERMEX), technical grade sodium carboxymethylcellulose (DRISCOSE), and sodium acid pyrophosphate (S.A.P.P.).

The averaged variations in resistivity of each additive with temperature are graphically shown and these variations have been further compared to those of a standard NaCl solution of fixed concentration. The variation of the ratios Rm/Rmf and Rm/Rmc with changing concentration and temperature was also studied.

It can be seen from the plotted results that the use of complex muds composed of two or more chemical additives will introduce problems into log interpretation which may not be solved by a theoretical approach. The natural additional of formation material to the mud as drilling progresses considerably complicates the situation. Therefore, the only practical answer is wellsite measurement of Rm, Rmf, and Rmc- of the actual mud compound in use at the time of logging and, for phosphate muds at least, these measurements should be made at a temperature corresponding as nearly as possible to the temperature of the reservoir.