Abstract: Depth of mud filtrate invasion is the basic parameter for evaluating mud filtrate-contaminated formation using conventional logging and for understanding the accuracy of reservoir evaluation parameters. There are various traditional methods to obtain this parameter, but they lack applicability and efficiency. Based on the formation sampling technology, the pumping process can be roughly divided into four stages using of the dynamic curve of the conductivity versus time. They are the startup phase, the initial phase, the transition phase and the stable phase. Based on this, the breakthrough time and stabilization time of formation fluid can be effectively determined. Combining factors of macro-stratum model, reservoir physical properties, pumping parameters, the invasion-depth-volume model has been established to quantitatively calculate the depth of mud-filtrate invasion. The influence of key factors such as formation lithology physical properties, fluid physical properties, instrument parameters, reservoir pollution degree on the calculation results is analyzed. In comparison with the traditional numerical simulation method, the new method is more efficient and reliable. This method has been applied to dozens of exploration wells offshore and have been achieved good results, thus providing an important basis for decision-making of field operation.

Key words: formation sampling, conductivity, mud filtrate, volume model, invasion depth