The Effect Of Potassium-Salt Muds On Gamma Ray, And Spontaneous Potential Measurements

Abstract Interpretations of the Gamma Ray and Spontaneous Potential curves generally assume sodium chloride to be the dominant salt in both the formation water and the mud filtrate. However, potassium-salt muds are increasingly being used by the oil industry. The potassium cation is significantly different from the sodium cation in its radioactive and electrochemical properties. Natural potassium contains a radioactive isotope which emits gamma rays. Thus, the presence of potassium salts in the mud system may contribute to Gamma-Ray tool response. Since the Gamma Ray is used quantitatively in many geological sequences as an indicator of clay content, a way to correct for the effect of potassium in the mud column is desirable. Correction methods and charts based on Laboratory measurements and field observations are presented ba this paper. The effect of temperature on the resistivity of potassium muds is also briefly discussed. From data available, it appears to be similar to that for NaCl muds. On the bases of field odservations and laboratory work, the electro-chemical properties of potassium-chloride and potassium-bicarbonate muds and mud filtrates are discussed. Activity relationships are proposed, and the influence of these salts on the SP component potentials—namely, the liquid-junction, membrane, and bi-ionic potentials—is described. Field examples are presented.