This paper presents a model for interference testing utilizing two horizontal wells of unequal lengths. The model presented is a semi-analytical model solution for interference testing utilizing two finite-conductivity horizontal wells having unequal lengths.
This model extends the previous interference testing model between two equal-length horizontal wells to a more general case in which the two horizontal interfering wells are of unequal lengths.
Sensitivity studies are performed to show the effect of horizontal well length on (1) Flux distribution in the active and observation wells, and (2) Pressure response in the active and observation wells.
Interference tests utilizing a pair of horizontal wells in a reservoir provide valuable information about the reservoir. Following the exposition regarding the use of source terms in solving unsteady-state flow problems in the reservoir (Gringarten and Ramey 1973), many dimensionless solutions have been presented for interference testing of horizontal wells (Achour et al. 2004, Babu and Odeh 1988, 1999, 2000, Clonts and Ramey 1986, Daviau et al. 1988). However, most of these solutions assume that the horizontal observation well is not influenced by the wellbore dynamics. Solutions for horizontal well testing involving pressure drop in the horizontal active well have been presented (Ozkan et al. 1995, 1995, 1997, 1999, Ding 1999, Penmatcha et al. 1999). Recently, Al-Khamis, et al. 2001, 2003, 2003 presented solutions for interference tests between horizontal wells incorporating the effects of wellbore hydraulics in both wells. The models (Al-Khamis, et al. 2001, 2003, 2003) closely approximate the actual scenario expected in a wellbore-reservoir system. These models however, assume that the interfering wells are of equal lengths.
The purpose of this work is to extend the semi-analytical solution (Al-Khamis, et al. 2001) for interference testing to handle two horizontal wells of unequal lengths. The model assumes an anisotropic but homogeneous reservoir in which the flow is single-phase and isothermal and the fluid is of constant compressibility and viscosity.
The model presents a system in which there is non-uniform flux distribution in both the active and observation horizontal wells. Due to the high conductivity of the observation well relative to the reservoir, the observation well serves as a flow path for reservoir fluids moving towards the active well. Thus, fluid is expected to enter the observation well from its far end and move towards the near end where it exits before approaching the active well.
In brief, the objective of this work is to:
Extend the semi-analytic model (Al-Khamis, et al. 2001) for interference testing between a pair of horizontal wells to handle cases in which the interfering wells are of unequal lengths, and
Study the effects of varying well lengths on pressure response in both wells.
This work follows the same approach used in Al-Khamis, et al. (2001, 2003, 2003) in coupling the reservoir and wellbore flow models and at the same time considers non-uniform flux distribution in both the active and observation horizontal wells. To obtain the wellbore flow model, a steady-state momentum equation for single phase isothermal flow in a horizontal wellbore was used. For this study, however, we have introduced a new dimensionless variable to account for the differences in the lengths of the active and observation wells.