Working offshore on a High Pressure / High Temperature gas well. We pumped 120 barrels of organic solvent into the well. The gas density was 0.3kg/m3. The fluid was 0.8kg/m3 & a boiling point of 85 degrees C (at 1 atm). The well is 5km long / deep. The initial surface pressure is 5,000 psi. The bottom hole temperature is +/- 180 degrees C. We pumped in fluid & saw surface pressure reduce to +/- 3,500 psi. We only pumped 2km worth of fluid. We pumped the fluid slowly & hoped it would fall to the bottom of the hole. However, it didn't. It remained suspended at surface. Can anyone explain why? Not sure if liquid is boiling & condensing at top of well. However, the closed in pressure is confusing the issue.
This answer is wrong, will remove when we have figured this out...
Could your well be filled with water, and the solvent floats on top? Water is liquid at these and pressures and temperatures. Liquids are nearly incompressible, so the density is just ~1kg/liter. Now you pour a liquid on top of that with a much lower density (do you really mean 0.8kg/m3 or rather 0.8kg/liter? ...anyway.) - so that will simply float on top of the water.