Downhole multistage choke technology to reduce sustained casing pressure in a HPHT gas well

• A technology of downhole multistage chokes to reduce annulus pressure has been proposed.
• The analytical model of downhole chokes, coupling pressure and temperature, has been established.
• The decreasing range of SCP has been calculated in a HPHT well with downhole chokes.

This paper describes a new downhole multistage choke technology for lowering the wellbore pressure and temperature profile of a high-pressure and high-temperature (HPHT) gas well. With the nodal system analysis of a gas well, the wellbore pressure and temperature distribution model of a downhole multistage throttle was established when coupling the throttling pressure and temperature dropping model. An example of a HPHT gas well was analyzed and also the choke hole diameters, numbers and positions of the downhole chokes were optimized according to the presets of the wellhead pressure, temperature and acceptable sustained casing pressure (SCP) in the A annulus. The results show that when adopting two-stage downhole throttling, the wellhead tubing pressure, average wellbore temperature, and the wellhead casing pressure in the A annulus have been decreased by 64.4%, 37.8%, and 43.6%, respectively, compared to the case with the surface choke technology. Therefore, using multi-stage throttling technology in HPHT gas wells can reduce wellhead pressure and wellbore temperature significantly, which can effectively lower the risk of SCP, ensure the integrity and security of wellbore and also greatly reduce the platform space for fixed offshore gas wells.