Streamtube Relative-Permeability Functions for Flashing Steam/Water Flow in Fractures
- J.S. Gudmundsson (Stanford U.) | A.J. Menzies (Geothermex Inc.) | R.N. Horne (Stanford U.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- July 1986
- Document Type
- Journal Paper
- 371 - 377
- 1986. Society of Petroleum Engineers
- 4.1.5 Processing Equipment, 5.3.2 Multiphase Flow, 5.2 Reservoir Fluid Dynamics, 5.9.2 Geothermal Resources, 1.10 Drilling Equipment, 4.1.2 Separation and Treating
- 2 in the last 30 days
- 132 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 5.00|
|SPE Non-Member Price:||USD 35.00|
The flow of steam/water mixtures into geothermal wells is analyzed by use of a two-phase model for flashing flow. The model includes the effect of heat transfer from the formation rock to the two-phase mixture. In the reservoir/well system, the two-phase flashing flow is assumed to occur in fractures. The model can be used to forecast the mass flow and enthalpy characteristics of two-phase geothermal wells. Relative permeability functions are derived for flashing steam/water flow in the permeability functions are derived for flashing steam/water flow in the feed-zone fractures of geothermal wells.
Flashing flow occurs when liquid water flows rapidly into a region where the pressure is below the saturation pressure of the water. In geothermal reservoirs, this can occur pressure of the water. In geothermal reservoirs, this can occur when liquid water flows toward the wellbore with a steep pressure gradient. Flashing steam/water flow in pressure gradient. Flashing steam/water flow in geothermal reservoirs is likely to be along fractures.
We consider the flow of steam/water mixtures in the feed-zone fractures of individual wells. The purpose is to report the use of a two-phase flow model where we assume flashing flow in planar fractures. The streamtube model of Wallis and Richter was modified to include the effect of heat transfer from the rock wall to the two-phase mixture as it flows rapidly toward a geothermal well. The model predicts the mass flow and enthalpy characteristics of wells that have two-phase feed zones.
The relative-permeability functions for steam and water are required in simulation and other studies of geothermal reservoirs. These functions, however, are not yet well known for geothermal reservoirs, and gas/oil data for porous media have to be used. This is not a satisfactory porous media have to be used. This is not a satisfactory situation because geothermal energy-recovery processes tend to be sensitive to the relative-permeability parameters used. Therefore, there is a need for better steam/water parameters used. Therefore, there is a need for better steam/water relative-permeability functions in reservoir engineering applications to fractured geothermal systems.
Flowing Geothermal Wells
Geothermal wells can be characterized by the mass flow and enthalpy of the steam/water mixture produced at various wellhead pressures. The fluid entering flowing wells in liquid-dominated reservoirs is commonly pressurized water or brine. The water (brine) flashes as it rises in the wellbore, and for most practical purposes, the enthalpy of the steam/water mixture is that of the pressurized water. The enthalpy is usually taken to be independent of wellhead pressure, although that is not always the case.
The fluid entering flowing wells in liquid-dominated reservoirs need not be pressurized water. It can also be a two-phase mixture of steam vapor and liquid water that results from flashing outside the wellbore. Well 403 in Tongonan, the Philippines, is an example of such a geothermal well. The mass flow and enthalpy of the steam/water mixture produced by Well 403 are shown in Fig. 1 at various wellhead pressures. The characteristic features of these data are the near-constant flow rate (mass flow) and the increasing enthalpy with decreasing pressure. The measurements show that the enthalpy of the fluid pressure. The measurements show that the enthalpy of the fluid that enters the well at low wellhead pressures is higher than at high pressures. There are at least two ways to explain this behavior: the well may have two or more feed zones (which produce different-enthalpy fluids in proportions dependent on the wellhead pressure) or the well may proportions dependent on the wellhead pressure) or the well may have a two-phase feed zone and flashing in the reservoir.
In addition to the flow-rate and enthalpy measurements shown in Fig. 1, flowing temperature and pressure surveys for Well 403 are available. Field analysis of the data indicates that the well has a major feed zone at 2000- to 2200-m [6,560- to 7,220-ft] depth and a minor feed zone at shallow depth that may contribute to the total flow at high wellhead pressures. The flowing surveys show that Well 403 has two-phase flow in the wellbore down to the major feed zone at 2000- to 2200-m [6,560- to 7,220-ft] depth. This indicates that the fluid entering the well is two-phase and probably results from flashing in the reservoir.
|File Size||465 KB||Number of Pages||7|