Implementation of Ensemble Kalman Filter (EnKF) Technique in Well-test Analysis of Gas Condensate Reservoirs

In this paper the Ensemble Kalman Filtering technique (EnKF) is implemented to remove noise from well testing data of a gas condensate reservoir and estimate some important parameters such as critical condensate saturation, irreducible water saturation and distribution index which can be used in drawing relative permeability curves. In order to use EnKF, we developed a MATLAB computer program which dynamically interfaces with ECLIPSE300 numerical reservoir simulator. The conventional approches for interpretation of transient data in gas condensate reservoirs can be criticized in several ways. Because of complex nature of flow in such reservoirs, many simplifying assumptions have been made in order to find analytical solutions for diffusivity equation which is theoritical foundation for most of well test analysis techniques , but these assumptions cause a great deal of error in final results. In addition to this, the available methodologies for well testing in such reservoirs are sensitive to measurment errors and flactuation in test data, consequently, any inaccurate mesuarment can be really misleading. Therefore, we used EnKF technique to cover the deficiencies appear in previous analysis methods. Furthermore, extracting relative permeability curves is the unique advantage of this technique.