Investigating the Role of Surfactant in Oil/Water/Rock Systems Using QCM-D

Abstract

Surfactants have been used for decades to enhance the production of hydrocarbons from oil-bearing subterranean formations. Production improvement is tied to optimization of the interaction of surfactant within a given oil/water/rock system. Ideal surfactants will alter the wettability and water/oil interfacial tension. While the mechanism of interfacial tension reduction is well-established, the mechanism of surfactant-driven wettability alteration is still up for discussion. This study aims to give insight into the matter by investigating the surfactant adsorption and desorption process using a quartz crystal microbalance with dissipation (QCM-D) apparatus. QCM-D is, in essence, an ultra-sensitive mass balance with nano-gram sensitivity. This technique exposes a sensor to flowing fluid at a controlled temperature and directly measures surface associations through the change in mass over time. Altering the material composition of the sensor surface, SiO2 for quartz and CaCO3 for calcite, and modifying the wettability with North American oil samples gives better representation of the surface interactions present in oil producing reservoirs. Surface activity for an anionic, cationic, non-ionic, and microemulsion surfactant were evaluated to determine both static and dynamic adsorption properties. The surfactant systems have drastically different static and dynamic adsorption properties. The charged surfactant had no measurable interaction with the quartz surface at 1 gallon per 1000 gallons (gpt). At higher concentrations the cationic surfactant reacted more slowly than the anionic and left more residual mass on the quartz and carbonate surfaces. Non-ionic surfactants had more measurable mass even at lower concentrations and the non-microemulsion had faster adsorption kinetics and was more resistant to washing off with fresh water than the microemulsion. The impact of job design for the various surfactant interactions with the silica surface was evaluated by altering the pumping schedules for the same volume of surfactant, showing the difference in accumulated residual mass on the surface using low concentrations throughout the fluid or front loading a concentrated plug volume. For charged surfactants, front loading was the least effective method; consistent concentration throughout the pumping schedule was more effective. Fast adsorbing surfactants quickly saturated the surface at high concentrations and had more effective loadings by splitting the surfactant into two equal medium concentration plugs. Ultimately, the surfactants were evaluated for removal of oil from the quartz surface. Without surfactant, very little oil is removed from the surface and it remained oil wet and fluorescent; the addition of surfactant improved the oil recovery by vastly different mechanisms. This study provides an understanding of surfactant adsorption processes on rock surfaces and the role of job design for mobilizing hydrocarbons. Understanding surfactant adsorption and its effect on wettability improves the current understanding on the matter.

Modeling of surfactant adsorption on coated quartz crystal surfaces during surfactant flooding process

“…that models the surfactant adsorption process in QCM tests can be obtained by replacing Eqs. (12) and (14) into Eq. (3) as:…”

“…Note that the QCM measures total mass and is not able to distinguish between different adsorbents. Hence, most QCM studies attempted to evaluate the effect of low-salinity brine and/or surfactant flooding on desorption of crude oil, have only tended to focus on one adsorbent [14,16,[29][30][31]. It is assumed that the surfactant adsorption is the same in the presence and absence of oil components at the crystal surface.…”

“…The combination of low salinity water injection and surfactant flooding (LSW-SF) is considered to be an economically attractive EOR approach, as high oil recovery and low surfactant retention was reported in core flooding tests [11]. In recent years, there has been an increasing interest in conducting QCM measurements for increased oil recovery processes prior to performing more time consuming core flooding tests [12][13][14][15][16]. A major advantage of running QCM experiment is its relatively fast technique for screening significant experimental parameters such as surface properties and crude oil.…”

The Influence of Oil Composition, Rock Mineralogy, Aging Time, and Brine Pre-soak on Shale Wettability

“…A look through the available literature indicates that the duration of the aging process that was employed for surfactant studies in shale varied from zero time up to a year (Figure ). ,,,,,,− This is worrying because several authors have presented the effect of the aging process on flow behavior. Jia et al investigated the effect of the aging time on the rock wettability measured on the Amott–Harvey index.…”

Calcium Carbonate-Modified Surfaces by Electrocrystallization To Study Anionic Surfactant Adsorption

“…With the aim of clarifying the surfactant adsorption process on mineral surfaces, the traditional depletion measurements of static tests (batch equilibrium tests on crushed core grains) and dynamic tests (core flooding measurements) are often used to determine the adsorbed amounts of surfactants. − However, these methods cannot monitor the kinetic processes in real-time and cannot quantify the structure of the adsorbed surfactant layer. More recently, quartz crystal microbalance with dissipation (QCM-D) monitoring has been extensively applied to study the adsorption behavior of surfactants, allowing for the real-time quantitative analysis of adsorption and desorption processes onto model mineral surfaces with nanogram sensitivity. − Sensors covered with model minerals can be obtained commercially, , fabricated by covering with core-shell microparticles, , synthesized in bulk or prepared using different processing methodologies such as layer-by-layer deposition , and electrochemical techniques. − In the latter, the formed mineral deposit is a product of electrochemically assisted reactions (acid–base reaction), followed by the electrochemically controlled redox reaction. For example, electrochemical pH modulation allowing for the formation of CaCO 3 coating on stainless steel substrates and silica deposition derived from sol–gel processing .…”