Use of a horizontal well for steam injection, or for fluid production in thermal recovery, is of practical interest in field operations. Experiments were carried out in a high pressure steam model equipped with an axially placed horizontal well. Steam was either injected into the horizontal well, or into the surrounding porous medium, with fluid production through the well. A variety of experimental conditions were employed. Temperatures and pressures were measured inside the well and at various points in the porous medium.
Several effects were clearly evident: gravity segregation of steam led to uneven heating of the porous medium. The distribution of heat along the well axis was quite uneven. Pressure drop inside the well was small, but it influenced fluid flow distribution in the surrounding porous medium. Oil recovery and pressure drop were plotted as functions of volume of steam injected. The production behaviour of the horizontal well could be correlated with temperature in the surrounding porous medium. Effects of well length, diameter, vertical position in the porous pack, oil viscosity, and pressure differential on oil recovery, oil-steam ratio, etc. were examined.
Over 2000 horizontal wells have been drilled for primary production in Alberta and Saskatchewan. A smaller number is used for thermal applications. Such applications utilize horizontal wells for production, injection, or both. Examples are: Tangleflags and Cold Lake, where horizontal wells are used for production, with vertical injectors, several cylic steaming type operations where horizontal wells are used for injection and production, and SAGD (Steam Assisted Gravity Drainage) in UTF and other areas where horizontal wells are used for both injection and production. There are more applications where horizontal wells are used as producers than injectors.
Flow of fluids and heat in the vicinity of a horizontal injector or producer is of interest in the above applications. The work described in this paper was concerned with an experimental investigation of fluid and heat transport around a horizontal producing well in a physical model that allowed for gravity effects. The flow of fluids inside the horizontal well was also studied via the measured pressure drop in the well. Several types of wells were tested. Effects of well length, diameter, and vertical location on performance were examined.
The advantages of horizontal wells, viz. large contact area with the reservoir, low pressure drawdown, and possible mitigation of coning, are well-known, and discussed in many papers. Likewise, field experience has been also been described in numerous reports. The success rate of horizontal wells as producers is about 60% in Saskatchewan. The experience with horizontal injectors is much more limited. Flow hydraulics and pressure drop inside a horizontal well have been the subject of several recent studies. Plaxton1 gives a comprehensive survey of treatments of pressure drop in horizontal wells, and reports an improved method.
The only previous study pertaining to flow inside a horizontal well and in the porous medium in the proximity of the well, under steam injection, was reported by Doan2 and Doan, Farouq Ali and George3.