Energy Geoscience (Jul 2024)
An experimental study on horizontal well waterflooding in the Cretaceous porous carbonate reservoir of Oman
Abstract
Porous carbonate reservoirs, prevalent in the Middle East, are lithologically dominated by bioclastic limestones, exhibiting high porosity, low permeability, intricate pore structure, and strong heterogeneity. Waterflooding through horizontal wells is commonly used for exploiting these reservoirs. However, challenges persist, such as significant uncertainty and complex operational procedures regarding adjustment effects during the exploitation. The USH reservoir of the Cretaceous D oilfield, Oman exemplifies typical porous carbonate reservoirs. It initially underwent depletion drive using vertical wells, followed by horizontal well waterflooding in the late stage. Currently, the oilfield is confronted with substantial developmental challenges, involving the understanding of residual oil distribution, effective water cut control, and sustaining oil production since it has entered the late development stage. Employing a microscopic visualization displacement system equipped with electrodes, this study elucidated the waterflooding mechanisms and residual oil distribution in the late-stage development of the USH reservoir. The results reveal that the reservoir's vertical stacking patterns act as the main factor affecting the horizontal well waterflooding efficacy. Distinct water flow channels emerge under varying reservoir stacking patterns, with post-waterflooding residual oil predominantly distributed at the reservoir's top and bottom. The oil recovery can be enhanced by adjusting the waterflooding's flow line and intensity. The findings of this study will provide theoretical insights of waterflooding mechanisms and injection-production adjustments for exploiting other porous carbonate reservoirs in the Middle East through horizontal wells.
