Borehole pressure and liquid level prediction of liquid-loading horizontal wells in West Sichuan

The technical key to drainage technology optimization and drainage parameter determination is to predict accurately the borehole pressure and liquid level of liquid-loading horizontal wells. The pressure balance model of tubing and tubing-casing annulus in liquid-loading horizontal well was developed based on the U-shape pipe principle by using fluid statics and dynamics equations. In this model, the tubing pressure drop is derived from the flowing gas above the liquid level and the two-phase flowing below the liquid level, and the two-phase liquid holdup is basically obtained from the drift model. The tubing-casing annulus pressure drop is derived from the static gas column pressure above the liquid level and the static liquid column pressure below the liquid level. The tubing pressure and the tubing-casing annulus pressure are equal at downhole connecting points. However, two liquid level parameters cannot be solved only by using one balance equation. To deal with this problem, the liquid level in tubing-casing annulus was measured by virtue of ground echometer, and then the liquid level and pressure in tubing were solved by means of the model. Case study indicates that by virtue of this method, the borehole pressure and liquid loading level in liquid-loading horizontal wells in West Sichuan Gasfield can be predicted accurately, and its prediction time efficiency is superior to that of traditional manometry. The influential factors were also analyzed. And it is indicated that the liquid level in tubing is generally higher than that in annulus, and the decrease of tubing-casing pressure difference can reflect indirectly the reduction of liquid loading volume in tubing.