Control of wasteful water injection is an important objective in optimizing waterfloods. Inefficiencies related to vertical sweep efficiency and some plausible corrective measures have been adequately covered in the literature. The purpose of this paper is to focus on areal sweep efficiency for a single layer assuming that, if needed, sub-zoning steps to minimize thief zone effects from other layers have been previously implemented.
In general, it is essential to minimize bypassing of otherwise recoverable oil and reduce channeling. The presence of geometrically complex connected and disconnected sand bodies creates challenges in maximizing areal sweep efficiency and in designing and managing efficient fluid injection projects. Traditionally, the practice in the industry has been to use simplified well spacing patterns. Many poor waterfloods started this way, using classical geometries without recognizing or honoring the inherent complexities of sand bodies in terms of competitive units with different hydraulic transmissivities.
We present a study highlighting the impact of improper well pattern selections that place injection wells in very high permeability channels. It can result in early elevated water-oil ratios and associated recovery losses because of a limited sweep of low permeability areas. This study is primarily focused on inappropriate placement of uniform well patterns in the presence of reservoir scale channel sands.
For a single layer, our study shows that the early rise in WOR and the deviation from linearity on the semi-log plot of WOR vs. cumulative oil is often indicative of early channeling and successive breakthroughs from tighter intervals. These scenarios can serve as monitoring tools to realign and relocate injectors that may have been unknowingly placed in high permeability channels.