Numerical study on the effects of wellhead restriction modes on the transient behaviors of a geothermal well deliverability applicable for short period of measurement

摘要

The transient behaviors of fluid, particularly on the stabilization time for a short period of artificial production test to establish deliverability curve is investigated numerically. Based on the experiences, the measured parameters, i.e. wellhead pressure and mass flow rate are taken when they are judged to be in stable condition. However, duration required for these variables to stabilize depends on flowing behavior of steam-water two-phase fluid in the wellbore. Additionally, the manner of controlling valve operation whether it starts from the well in full-opened condition or in full-closed condition seems to affect this flow stabilization. Thus, transient behaviors of well deliverability are analyzed numerically using a coupled reservoir-wellbore simulator. To evaluate the effects of the manner and the duration of valve controlling operation on well deliverability, a step change and linear changes with several time intervals in mass flow rate at the wellhead are given. The results show that for the same magnitude of flow rate increase and decrease changes, the fluid will stabilize faster for the condition when the valve operation starts from the well in opened condition in comparison to that in closed condition. Another result indicates that duration required for wellhead pressure to stabilize for a given mass flow rate increase in a form of step change is longer compared to that in the form of linear changes. The longer time applied for operating valve will result in the faster stabilization of wellhead pressure after operating valve is stopped.