Several methods have been deployed for artificial lift in deep long horizontal wells completed in unconventional reservoirs. Some methods have been successful whereas some others have failed. In our study, we investigated the various lift mechanisms and derived an envelope for their application to such horizontal wellbores using a sensitivity study through a transient fluid-flow wellbore model.
A calibrated earth model from the Eagle Ford Shale basin with hydraulic fracture geometries in the horizontal wellbore was used for the sensitivity study. The wellbore profile was changed in the simulation model to four different types of profiles: toe up, toe down, toe up with hold trap, and toe down with hold trap. Other factors such as location of the artificial lift equipment in the wellbore, reservoir performance, and deliverability were considered for the deployment of the artificial lift method. Transient fluid-flow wellbore simulations and numerical reservoir simulations were used to determine the performance potential and effectiveness of the artificial lift mechanism for long-term productivity.
Multiphase fluid flow and transient flow phenomenon are critical modeling considerations for horizontal wellbores. It was found that the critical flow rate in horizontal wells can vary considerably when the well profile is considered. As the drilling dogleg severity increases, the chances of wellbore slugging and liquid holdup increase. Additionally, with producing time, the conditions change. In a gas lift well, if the gas injection rate is maintained above the critical rates as determined in this study, the production issues can be controlled. Therefore, it is clear from this study that the well trajectory and drilling uncertainty window must also account for the artificial lift method that is planned to be deployed. Adjustments to the artificial lift method placement in the wellbore would help offset negative impacts if the wells are poorly drilled.
Recommended practice for drilling, completion, and artificial lift can be derived from this study. Integration of the artificial lift selection to the earth model, drilling trajectory and landing, hydraulic fractures, and the completion model is paramount to improve the efficiency of artificial lift in the unconventional reservoirs.