Comparison of vertical, slanted, and horizontal wells productivity in layered gas-condensate reservoirs

The performance of a horizontal (highly slanted) well (HW) or a slanted well (SW), is generally believed to be better than that of a vertical well (VW) due to its greater exposure to the reservoir. However, the costs of drilling and completion are more and the options for monitoring, control and intervention often limited. Gas-condensate reservoirs are increasingly considered as suitable candidates for drilling SWs or HWs. These reservoirs pose special challenges selecting one type or the other due to the complex nature of fluid flow in porous media exhibited by these low interfacial tension systems, which are different from those of conventional gas-oil systems.

In this study we have investigated the performances of SW, HW and VW in both single-layer homogenous and layered gas-condensate reservoirs. ECLIPSE 300 compositional reservoir simulator, which includes our in-house relative permeability (kr) correlation accounting for the coupling (increase in kr by an increase in velocity and interfacial tension) and inertial (decrease in kr by an increase in velocity) effects, has been used to conduct a series of sensitivity analysis on a single-well model resulting in some important practical guidelines. The effect of fluid properties and that of reservoir anisotropy (vertical to horizontal permeability ratio, kv/kh) have also been studied.

For homogenous systems, HW and SW have higher productivities. The improvement due to increase in lateral reach is less pronounced at lower kv/kh values especially for SW. In the case of layered reservoirs, the productivity of SW is adversely affected by the extended cross flow from low permeability to high permeability layers. In this case the impact of position of layers and that of kv/kh is more pronounced for SW and both at lower kv/kh. The decrease in velocity around the wellbore of HW decreases the impact of kr velocity dependency on production.