Enhancing oil recovery from low-permeability reservoirs with a self-adaptive polymer: A proof-of-concept study

Abstract

Considerable success has been achieved in enhanced oil recovery by polymer flooding from high- to medium-permeability reservoirs; however, the poor injectivity and ease of mechanical degradation of the commonly used high-molecular-weight (high-MW) partially hydrolyzed polyacrylamides (HPAM) impede their use in low-permeability reservoirs. To alleviate these issues, we proposed the use of the self-adaptive polymer (SAP). SAP with a relatively low MW (8.7 × 106 g mol−1), a rigid unit, and hydrophobic pendant group was prepared and compared with its counterparts HPAM-1 (8.2 × 106 g mol−1) and HPAM-2 (24.9 × 106 g mol−1). It was found that while the molecular size of SAP is similar to that of HPAM-1, its thickening capability is stronger under identical conditions, and both of them can be smoothly injected into the 60-mDarcy cores. By contrast, HPAM-2 causes fatal plugging in this scenario. The favorable injectivity of SAP solution stems from its reversible viscosity change in response to shear forces without any deterioration, which is achieved by the association-disassociation transition of molecular chains. In the elongational field, both SAP and HPAM-1 do not degrade mechanically, as opposed to the case of HPAM-2. More significantly, SAP can improve oil recovery up to 18.7%, which is around three times higher than that of HPAM-1. This self-adaptive concept may open a new pathway for the molecular design of polymers used for enhancing oil recovery in low-permeability reservoirs.