Hydrocarbon Thickness Fluctuations in Monitoring Wells

Abstract Hydrocarbon thickness measurements in monitoring wells are used to estimate the hydrocarbon volume in the subsurface and to evaluate the efficiency of hydrocarbon recovery. It is commonly assumed that the formation hydrocarbon thickness is linearly related to the measured one. However, field data quite frequently show hydrocarbon thickness fluctuations that are not related to either hydrocarbon recovery or its release. It is postulated that these fluctuations are related to hydrocarbon/ground‐water interface elevation changes, and can be explained by two mechanisms: (1) difference in the residual saturation of hydrocarbons entrapped below and above the “interface,” and (2) preferred flow of the liquids through the monitoring well.