On-Demand Water Control: Molecular Host-Guest Interaction for In-Situ Modification of Formation Fluid Permeability

Abstract

Hydrophobically modified hydrophilic polymers (HMHPs) have numerous applications in the petroleum industry, among which stand out relative permeability modifiers (RPMs) for acid diversion, drilling, fracturing, water control, water-injection profile modification, or improved oil recovery (IOR) operations. The efficacy of the polymeric RPM is attributed to a bimodal mechanism of action, which involves the association of the hydrophobic appendages in addition to adsorption of the amphoteric material to the formation surface. As a result, one challenge associated with the use of HMHPs is the pressure increase often observed when the material enters the formation. A second limitation is the inability to reverse the effect of the treatment fluid, which can be significant when the HMHP is overdisplaced, resulting in a reduction of flowback fluid, or when operational requirements call for placement of a deactivated HMHP that can be selectively activated at a desired time and location. Because of the self-diverting nature of the HMHP discussed in this paper, field deployment has been limited to near-wellbore (NWB) applications. Within this context, a linear surfactant additive [sodium dodecyl sulfate (SDS)] has been an effective mitigation strategy against such self-diverting characteristic; however, this also inhibits other desirable HMHP properties. Restoration of the native RPM properties was achieved using a surfactant control agent that allows on-demand RPM reactivation. Recently, it was realized that the sodium dodecyl sulfate has a much higher affinity for hydroxypropyl-β-cyclodextrin (HPCD) than HMHP. This paper discusses developments that allow for improved injectivity of HMHPs when used as RPMs for water-control operations. In addition, this study attempts to advance the existing understanding of the performance and associative mechanism of action of RPMs. Currently, there is a lack of consensus about the role hydrophobic modifications play in HMHP performance. Using host-guest attraction, the nature of the hydrophobic moieties is revealed, which compliments the current body of literature related to the use of HMHP in the petroleum industry. To this end, adsorption, fluid loss, and coreflow results prove the increased affinity of the surfactant for HPCD serve to release HMHP from the HMHP/linear-surfactant complex, reactivating the HMHP to its original associative mechanism-based RPM-performance profile.