UC Berkeley

Low salinity water flooding (LSW) has gained significant attention, because of its advantages comparedwith other enhanced oil recovery (EOR) methods. LSW's positive contribution to recovery factor has beendemonstrated in the literature at lab and field scales. However, LSW flooding does not always incrementoil recovery. It is a specific combination of properties of an asphaltenic crude oil, chemically equilibratedbrine, and rock surface that may explain the success or failure of LSW. In this work, we introduce anovel experimental approach to study asphaltene-like chemical interactions with surfaces rock minerals toevaluate the effectiveness of applying LSW. When studying the impact of asphaltene properties on incremental recovery, one aims to detach someof the immobile oil, which is semi-irreversibly stuck on rock surface. This is a difficult task, because ofvarying crude oil composition, as well as asphaltene interfacial and chemical properties. To overcomethese issues, we split the problem into several parts. We study how mono- and poly-functional chemicalcompounds mimic asphaltene interactions with mineral surfaces, like silica and calcium carbonate, whichare proxies for sandstones and limestones, respectively. For example, amines, quaternary ammonia orcarboxylates represent asphaltene functional groups that are mainly responsible for crude oil base andacid numbers, respectively. Adsorption of polymers and oligomers containing such groups mimics theirreversible asphaltene deposition onto rock surface through formation of chemically active polymerlikestructures at the oil-brine interface. The silica surface is negatively charged in brines with pH above 2. Silica attracts positively chargedammonia salts, such as cetrimonium chloride (CTAC). However, negatively charged mono-functionalcarboxylates, i.e. anionic surfactants, like sodium hexanoate (NaHex), hardly adsorb onto silica, even in thepresence of a bridging ion, like calcium. In contrast to silica, calcium carbonate surface has both positive and negative charges on its surface. Wefound that CTAC adsorbs onto calcium carbonate in any brine tested. NaHex shows minimal adsorption onto calcium carbonate only in the presence of calcium ions suggesting a contribution of an ion-bridgingmechanism. Adsorption of all studied mono-functional surfactants is fully reversible and, consequently notrepresentative of asphaltenes. Multifunctional compounds, i.e., polymers, demonstrate irreversible,asphaltene-like, adsorption. We studied adsorption of carbohydrates decorated with individual amines andquaternary ammonia functional groups. The carbohydrates with amine functional groups adsorb irreversibly on calcium carbonate and silica inall tested brines with pH up to 10. Therefore, a lower base number (BN) in crude oils indicates a higherpotential for LSW. Our findings demonstrate the proof of concept that contribution of different functional groupsto asphaltene adsorption/deposition can be studied using functionalized water-soluble polymers. Thisframework is useful for assessment of adsorption strength vs. number of active groups as well as screeningof efficient detachment process of asphaltenic crude oils from rock surface.