Inflow Performance Relationships, IPR, are quantitative estimates of the productive potential of a well-reservoir system. Through this relationship, engineers determine basic elements such as the optimum production scheme and artificial lift design and operation. Several authors studied IPR in vertical and deviated wells considering two and three-phase flow in light oils. Other studies have also estimated productivity index for horizontal and slanted wells but only based on single-phase flow. All of them have not explicitly included how the oil API gravity affects the performance.
Since a large amount of the world oil reserves are heavy oils, the goal of this research is to generate a general Vogel type correlation valid not only for light oil reservoirs but also for heavy oils. The experimental study, performed with numerical reservoir simulation, was run over variables such as: permeability; relative permeability curves; reservoir pressure, degree of depletion, and PVT fluids properties. Due to the huge advantage of horizontal and deviated wells for producing heavy oil, vertical to horizontal permeability ratios was also analyzed within different angles of inclination. Furthermore, different water cuts were generated for vertical wells using reservoir water saturation in order to evaluate the effect of this variable over the IPR.
A general correlation for the V coefficient of Vogel's equation was generated that depends on the angle of inclination of the well, and several reservoir and fluids characteristic. Additionally, reservoir depletion was addressed through the reservoir pressure ratio with respect to the bubble point pressure. The application of the relationship described in this study is simple and only requires common known parameters of the field.
Introduction
A daily operation of an engineer considers inflow performance of the reservoir to the producing wells. This information is a key factor for optimizing the well, the artificial lift and surface equipment, and for evaluating the different exploitation schemes of a field. This behavior is defined by the relation between the production rate and the bottom-hole flowing pressure and it is known as the inflow performance relationship, IPR.
Several inflow performance relationships for vertical wells have been developed(Gallice & Wiggins, 2004). The existing correlations have been developed for light and medium crude oils. Due to huge world heavy oil reserves, discovered in last decades mainly through vertical wells, there is a necessity to validate the application of those models for heavy oil wells or, to generate new IPR models for this purpose. The influence of rock and fluids characteristics must also be studied.
Horizontal and inclined wells have been used to optimize reservoir exploitation; these wells exert great advantages compared to vertical wells. Horizontal wells have been used in cases as thin zones; naturally fracture reservoirs; avoiding gas or water coning; low permeability sands; tight gas reservoirs; and viscous heavy oil production. Horizontal wells have been drilled in order to efficiently produce heavy oil reservoirs.
Vertical correlations may not apply for horizontal wells for two main reasons; the flow into the tubing is a combination of linear and radial streamlines. The second reason is related to permeability, both horizontal and vertical permeability play an important role in this case and the anisotropy is a key parameter (Kamkom & Zhu 2005). Several authors have studied the inflow performance of horizontal and inclined wells through analytical methods (Babu & Odeh 1988, Elgaghad et al 1996, Joshi 1998). They are mainly based on single phase models derived from Darcy equation; they may have little application in multiphase reservoirs, though. Several authors have carried out reservoir simulations in order to study the inflow of solution-gas reservoirs in horizontal wells (Bendakhlia & Aziz 1990, Cheng 1990, Kabir 1992, Retnanto 1998, Wiggins & Wang 2005, GarcÍa & MartÍnez 2008). They have proposed inflow performance relationships to predict the production-pressure behavior. Similar to vertical wells, the effect of fluid characteristics such as API gravity and viscosity has not been analyzed in those studies.
