The paper describes a practical case of using multi-well pressure Pulse-Code Testing (PCT) for assessment of inter-well connectivity and potential reserves for placement of new wells in off-shore environment. The study was based around two PCT cells (one calibration and one scanning) which were surveyed on the same platform within one month.
The calibration PCT cell was set around injectors in peripheral area to eliminate the uncertainty in reservoir saturation, and provided estimation of macroscopic reservoir permeability (ka) and macroscopic rock compressibility (cr) in cross-well intervals. The reservoir permeability was found to be in good correlation with core-calibrated log prediction, while rock compressibility turned out to be twice higher than expected. Additionally, the calibration PCT cell picked the seismic fault as being impermeable and provided accurate values of its proximity to the pulsing well and its extension in the north direction. The sealing nature of this fault explains poor aquifer support in the southwest of the field. The acquired information helped to improve matching of formation pressure in the dynamic model.
The scanning PCT cells identified the baffle in the southern part of the field, which was later interpreted as the bank failure of the meandering river flow. The study concluded that injection in river bedding is detrimental to uniform water flood pattern and should be avoided. The vertical sweep efficiency from PCT study was varying in different directions and helped to calibrate facies distribution and shale breaks. Some wells showed anomalous PCT behavior and were suspected of water production from thief zones, which was later picked by advanced production logging, based on spectral noise logs and temperature modelling.
The fine-grid 3D model was calibrated both on static and dynamic data including the newly acquired framework of PCT and advanced production logging. The analysis of the new model has located the areas of low mobility oil due to poor communication between injectors and producers in these areas. These areas were recommended for infill drilling as well as for rearranging the water injection pattern to improve the sweep and pressure support pattern. The production and water cut of the newly drilled horizontal well showed a good match with the calibrated model prediction.