1999 Volume 21 Issue 2 Pages 115-126
In this paper, a calculation method of pressure loss in mist flow region has been developed and included in the wellbore flow simulator WELCARD-IV. This simulator is a modified version of WELCARD-III and applicable up to mist flow in geothermal wells. The validation of the simulator using measured data of nine wells in the Kakkonda and the Mori geothermal fields has been verified. The results are as follows:
1) When the steam quality is above 0.145, the fluid flow in the geothermal wells transforms from annular-mist flow to mist flow. In the strict sense, the mist flow in this paper is defined as the broken liquid film annular flow.
2) In the mist flow regime, the friction loss between the flowing fluid and the wall of the geothermal well is estimated accurately by the following formula.
ΔPf=4τw/D(1-w)dl Where p Pf is the friction loss, τw is the shear stress, D is the well diameter and dl is the length of element. Parameter w is defined as a function of void ratio α as follows:
w=0 at α<0.9
w=(10α -9)2 (21-20α) at α≥0.9
3) The average density of two-phase (steam and hot water) fluid(ρm) calculated by the following formula estimates the head loss accurately.
ρm=[1+(1/χ-1)e]/[1/ρg+(1/χ-1)/ρL e]Where χ is the quality, ρ is the density and subscripts g and L show gaseous and liquid phases, respectively. Parameter e is defined as ratio of the mass of liquid phase flowing in the homogeneous mixture to the total mass of water flowing in the annular flow regime and given to be 0.9 in the mist flow regime.
4) A comparison between computational results using WELCARD-IV and the measured values of borehole temperature and pressure during production in the Kakkonda and the Mori geothermal fields was carried out, and the computational error was within 5%.
