Production performance by polymer conformance control in ultra-low permeability heterogeneous sandstone reservoirs produced under their natural energy

Abstract For ultra-low permeability and highly heterogeneous sandstone reservoirs, fluid channeling along the high permeability layer leads to a rapid decrease of reservoir pressure coupled with very low sweep efficiency. As an effective conformance control technology, advanced polymer injection can enhance oil production from ultra-low permeability heterogeneous sandstone reservoirs, not only through conformance control but also through increasing reservoir energy. In order to simulate the reservoir energy storage capacity during the polymer injection stage as well as accurately control the energy release rate during the production stage, a novel experimental setup is assessed in this study. Partially hydrolyzed polyacrylamide (HPAM) is used as the polymer conformance control solution. Artificial heterogeneous sandstone cores are used to perform a series of polymer conformance control followed by production under the natural energy of the model reservoir. The effect of polymer injection volume and its concentration on polymer retention and plugging ability are investigated. Without polymer injection, the initial volume of produced liquid is large, however rapidly declines leading to a poor overall oil recovery. This trend accurately captures field performance. Upon advanced polymer injection, although the initial volume of produced liquid relatively decreased, the decline in the rate of liquid production decreases. The reservoir pressure in the later stages of production could still be maintained at a relatively higher level. Subsequently, the production period is prolonged, leading to a significant increase in oil recovery. The increase in the polymer injection volume or polymer concentration delayed polymer evolution from the reservoir, suggesting enhanced polymer plugging ability. Optimal polymer volume of 0.3–0.6 PV at its optimal concentration of 3000 mg/L corresponding to highest oil recovery is attained at the reservoir conditions. In this study, advanced polymer injection is proved to be a feasible technology to significantly improve the sweep efficiency in ultra-low permeability heterogeneous sandstone reservoirs. By controlling the appropriate polymer injection volume and its concentration, the highest recovery of a certain reservoir can be reached. For the oilfield engineers, by virtue of its ability to faithfully capture field trends, the proposed experimental setup may offer a reliable method to determine the optimal polymer injection volume and concentration for given reservoir conditions and characteristics.