Description: Sigma hydrocarbon (Σh) for gas or oil can be determined by using this chart. Sigma hydrocarbon is used to calculate the water saturation of a formation. One set of charts is for measurement in metric units and the other is for measurements in “customary” oilfield units. For gas, enter the background chart of a chart set with the reser-
voir pressure and temperature. At that intersection point move left to the y-axis and read the sigma of methane gas. For oil, use the foreground chart and enter the solution gas/oil ratio (GOR) of the oil on the x-axis. Move upward to intersect the appropriate API gravity curve for the oil. From this intersection point, move horizontally left and read the sigma of the oil on the y-axis.
Source: © Log Interpretation Chartbook (2009), Schlumberger