EXPERIMENTAL STUDY AND THEORETICAL ANALYSES OF FORMATION RESISTIVITY UNDER FRESH WATER FLOODING

摘要

In oil exploration and oil field development, marking off hydrocarbon zones mainly depends on resistivity logs. Formation resistivity is affected not only by hydrocarbon saturation but also by formation water salinity. However, in water flooded areas, formation water is often variable. Combining the laboratory displacement measurements and theoretical analyses of the resistivity change during the water flooding processes, this paper investigates the characteristics of the electric properties of core in the process of decreasing oil saturation under fresh water injection for Liudong Oilfield, China. As low salinity water invades the rock sample, resistivity first decreases and then increase, forming a U-type curve. In some samples, the resistivity then starts to decrease again, as water saturation continues to increase, forming a sigmoidal one. This paper also points out the controlling factors on the relationship, namely the irreducible water saturation, the salinities of formation water and injected water. The research provides a reliable guidance to formation evaluation under fresh water flooding.