Evaluation of the Downflow Effect on the Well X to Reservoir Temperature Decrease in the Field Y Using PetraSim Geothermal Reservoir Simulation

Abstract

The "Y" field is one of the geothermal fields which produces two-phase fluid in the form of steam and water which is dominated by water. However, one of the wells in the field produced a single-phase fluid in the form of dry steam, namely the "X" Well. This is because the "X" well has four feed zones, where the shallower feed zone becomes a source of production (inflow) in the form of a steam cap, whereas the deeper feed zones do not produce geothermal fluid. After all, it has died due to downflow or cold-water flow from shallow feed zone that goes down. This causes the flow of fluid in the deep feed zones can’t come out due to the pressure which is less than the pressure of the downflow. The inflow is from the feed zone located at a depth of 2,500 - 3,000 ft, while the downflow at the feed zone is located at a depth of 2,630 - 4,734 ft MD (from the negative PTS survey results). Besides turning off the deeper feed zones, this downflow can also cause a decrease in temperature in the reservoir field. If the temperature drop in the reservoir lasts for a long time it is possible to cause the reservoir to become dead due to cooling. Therefore, the effect of downflow to changes in temperature in the reservoir must be analyzed. With PTS "X" well survey data, a simulation will be conducted using PETRASIM software to see the effect of the downflow. From the simulation, the result of temperature decrease for 60th, 100th, 200th and 300th year of simulation time setting is 0.25%, 0.58%, 1.42%, and 2.21%. For temperature decrease per year is 0.0042%. so, the results show a very small decrease in reservoir temperature, so that the reservoir is still in good condition even for the next 300 years.