Publications

The Tanjung Field, as one of PT Pertamina EP’s mature fields, has been subjected to waterflood since the 1990’s to increase oil production rate and, ultimately, the oil recovery. The complex Tanjung Structure is composed of multilayered reservoirs, thus the density changes from the waterflooding process are hard to predict due to the complexity of data within the reservoirs itself that need to be confirmed with the process, such as volume of water injection, oil production and formation pressure per layer. Not to mention that most wells are produced commingledly. A geophysical method, time-lapse microgravity, was approached to monitor waterflood mobility within these complex reservoirs. Fluid density change in the reservoirs were analyzed over a six months interval (November 2014 and April 2015) in order to obtain a clearer picture between the production-injection relationship in this area. Vertical Electrical Sounding (VES) and rainfall data was also used to eliminate shallow groundwater influence to the microgravity values. Five high-rate injection wells nearby producer wells were used as key wells to validate the results from this method. The result divides the study area into four blocks according to different characteristics due to density change, influenced by NW-SE fault. Block I and Block III have negative anomaly, indicating lack of water injection over these areas. Block II has balance index of injection-production rate by zero gravity anomaly, whereas Block IV shows an undersaturated reservoirs condition with positive anomaly. Formation pressure of X and Z layers in key wells acquired from 4D microgravity results, which has similarity with actual formation pressure data, shows unsignificant change in formation pressure, indicating that the waterflood process was well executed. Time-lapse microgravity was well applied at the Tanjung Structure to monitor waterflood perfomance. Deconvolution Simulation of Mass Volume Density (DSMVD) is planned for further research to identify fluid movement in each reservoir due to density change.