Jin, Luchao (University of Oklahoma) | Budhathoki, Mahesh (University of Oklahoma) | Jamili, Ahmad (University of Oklahoma) | Li, Zhitao (The University of Texas at Austin) | Luo, Haishan (The University of Texas at Austin) | Delshad, Mojdeh (The University of Texas at Austin) | Shiau, Ben (University of Oklahoma) | Harwell, Jeffrey H. (University of Oklahoma)
The surfactant screening process to develop an optimum formulation under reservoir conditions is typically time consuming and expensive. Theories and correlations like HLB, R-ratio and packing parameters have been developed. But none of them can quantitatively consider both the effect of oil type, salinity, hardness and temperature, and model microemulsion phase behavior.
This paper uses the physics based Hydrophilic Lipophilic Difference (HLD) Net Average Curvature (NAC) model, and comprehensively demonstrated its capabilities in predicting the optimum formulation and microemulsion phase behavior based on the ambient conditions and surfactant structures. By using HLD equation and quantitatively characterized parameters, four optimum surfactant formulations are designed for target reservoir with high accuracy compared to experimental results. The microemulsion phase behavior is further predicted, and well matched the measured equilibrium interfacial tension. Its predictability is then reinforced by comparing to the empirical Hand's rule phase behavior model. Surfactant flooding sandpack laboratory tests are also interpreted by UTCHEM chemical flooding simulator coupled with the HLD-NAC phase behavior model.
The results indicate the significance of HLD-NAC equation of state in not only shorten the surfactant screening processes for formulators, but also predicting microemulsion phase behavior based on surfactant structure. A compositional reservoir simulator with such an equation of state will increase its predictability and hence help with the design of surfactant formulation.
This paper presents a dynamic wettability alteration model based on the Gibbs adsorption isotherm equation. The model is conceptually and thermodynamically developed for ideal surfactant solutions (
The developed models can be tuned with experimental data including the contact angle, relative permeability, and capillary pressure parameters then they can be used to predict the efficiency of surfactant injection processes in naturally fractured reservoirs accordingly.
SmartWater flooding through injection of chemistry optimized waters by tuning individual ions is recently getting more attention in the industry for improved oil recovery in carbonate reservoirs. Most of the research studies described so far in this area have been limited to studying the interactions at rock-fluids interfaces by measuring contact angles, zeta potential, and adhesion forces. The other widely reported interfacial tension data at oil-water interfaces do not consider the formation of interfacial monolayer and the interfacial tension is estimated as an average parameter relying on the properties of two individual bulk phases. As a result, such measurements have serious shortcomings to provide any details on complex microscopic scale interactions occurring directly at the interface between crude oil and water to understand the SmartWater flood recovery mechanism.
In this study, two novel interfacial instruments of interfacial shear rheometer and surface potential sensor were used to study microscopic scale interactions of various individual water ions at both air-water and complex crude oil-water interfaces. The measured interfacial rheology data indicated totally different interfacial behavior at crude oil-water interface when compared to air-water interface due to presence of crude oil functional groups. Viscous dominated response was observed at crude oil-water interface for all brine compositions. These interfaces behaved like a viscous fluid without exhibiting viscoelastic solid like properties. Lower interfacial viscous modulus was observed for certain key ions such as calcium, magnesium, and sodium. The interfacial viscous modulus was found to be substantially much higher for sulfates, besides exhibiting some elasticity. The surface potential was gradually decreased by replacing seawater with calcium only brine. The better surface activity with seawater can be attributed to adsorption of more key water ions at the surface.
The interesting results observed with certain water ions at fluid-fluid interfaces are expected to work in tandem with rock-fluids interactions to impact oil recovery in SmartWater flood. At first, they play a role to control the accessibility of active water ions to approach the rock surface, interact with it and subsequently alter wettability. Next oil droplets adhering to the rock surface will be detached and released due to favorable interactions occurring at rock-fluids interfaces. The interfacial film between oil and water can then quickly be destabilized due to less viscous interfaces observed with certain ions to promote drop-drop coalescence and easy mobilization of released oil droplets. This coalescence process is sequential and it would continue until the formation of small oil bank.
This is the first study that showed added importance of fluid-fluid interactions in SmartWater flood by using direct measurements on individual water ions at crude oil-water interface. In addition, a new oil recovery mechanism was proposed by combining both the interactions occurring at fluid-fluid and rock-fluids interfaces. The new fundamental knowledge gained in this study will provide an important guidance on how to synergize water ion interactions at fluid-fluid interfaces with those at rock-fluids interfaces to optimize oil recovery from SmartWater flood.
In the case of surfactant EOR, an optimum formulation of surfactant has to be injected in the reservoir. This so-called optimum formulation corresponds to a minimum in the interfacial tension and a maximum in oil recovery and may be obtained with an appropriate balance of the hydrophobic and hydrophilic affinities of the surfactant. Salinity—scan tests are generally used to screen phase behavior of surfactant formulations before conducting time-consuming coreflood tests. The objective of this study was to develop a high-throughput dynamic microfluidic tensiometer, with the aim of studying interfacial phenomena between EOR injected formulations and crude oils and of optimizing chemical EOR processes for pilot or field applications.
We have selected a method based on the Rayleigh-Plateau instability and the analysis of the droplets to jetting transition in a coaxial flow of two fluids. In fact, in coaxial flows, the transition between a droplet and a jetting regime depends on the velocities of each phase, the viscosity ratio, the confinement and the interfacial tension (IFT). As the three first parameters are known, the dynamic interfacial tension can be calculated. This microfluidic device has been specifically designed to support high temperatures (up to 150°C), high pressures (up to 150 bars) and is compatible with complex fluids such as crude oils and solutions of surfactants and polymers.
The method was first developed and validated on a microfluidic device on model fluids at ambient temperature and atmospheric pressure for IFTs higher than 1 mN/m. It was then successfully applied for the measurement of IFTs over more than four decades. Measurements were also performed with a crude oil and a typical surfactant formulation. The validation of the HP/HT assembly, which has been designed with the aim to work in reservoir conditions, is currently under progress. By using this tensiometer, it would be quite easy to perform in short time numerous salinity scans on real systems in order to get the evolution of IFT and determine the optimal salinity S*.
Prieto, C. A. (CEPSA Research Center) | Rodriguez, R. (CEPSA Research Center) | Romero, P. (CEPSA Research Center) | Blin, N. (CEPSA Research Center) | Panadero, A. (CEPSA Research Center) | Escudero, M. J. (CEPSA Research Center) | Barrio, I. (CEPSA Research Center) | Alvarez, E. (CEPSA Research Center) | Montes, J. (CEPSA EP) | Angulo, R. | Cubillos, H.
The design of an alkali-surfactant-polymer (ASP) formulation for chemical Enhanced Oil Recovery poses multiple challenges from the experimental point of view. The present research examines the laboratory procedures and experimental results aimed at selecting the most suitable chemicals for an ASP pilot trial at the Caracara Sur field (Los Llanos Basin, Colombia). The key challenge was the limited compatibility of the surfactant and polymer selected under reservoir conditions (temperature and total salinity), leading to phase separation of the ASP solution and losses of the activity of both chemicals. An extension of the experimental program was required to re-design the formulation and mitigate risks of damaging the formation in the following field trials. The formulation comprised an alkyl benzene sulfonate as main ingredient, a hydrolyzed polyacrylamide as viscosifying agent and some weak alkali to reach the optimum salinity of the mixture. A mono-alkyl diphenyl disulfonate ether was added as coupling agent to improve compatibility of the ASP mixture. The performance of the selected ASP formulation was assessed by means of interfacial tension measurements, long-term thermal stability tests and dynamic core-flooding tests. The formulation provided ultra-low interfacial tension (< 10-2 mN/m) and viscosity enough to assure an appropriate mobility control. Hence, the formulation was considered to be suitable for further testing in the field pilot.
Recovery from oil reservoirs could be improved by lowering the injection water salinity or by modifying the water injection chemistry. This has been proposed as a way to increase rock water-wetness. However, we have observed that the presence of sulfate anions in the aqueous phase can change the crude oil-water interfacial rheology drastically, and as a result, the oil recovery factor could be increased solely by alteration of fluid-fluid interactions. The purpose of this research is to show the effect of sulfate anion concentration in seawater injection on oil production through coreflooding results at low temperature.
Interfacial rheological experiments were run with several crude oils and modified seawater to see the effect of different ions on visco-elasticity of the crude oil-brine interface using an AR-G2 rheometer with a dual-wall ring fixture. Based on previous experimental results, carefully selected coreflooding experiments were run to evaluate differential pressure and oil recovery for each selected brine. Coreflooding experiments used Indiana Limestone at 25°C without aging to minimize changes in rock wettability.
The interfacial rheological results show that the visco-elasticity of the crude oil-brine interface is higher for a low-salinity brine compared to a higher-salinity one when individual salts are used, e.g. NaCl or Na2SO4. The difference is more pronounced if ultralow salinities are compared. For the cases with salinity values similar to that of seawater, the effect of sulfate concentration in water on interfacial visco-elasticity is more noticeable. Coreflooding results show that brines with a higher visco-elasticity, corresponding to a higher sulfate concentration in the water injected, yield higher oil recovery factor that those with lower visco-elasticity, including the experiments with salinity lower than 50% of that of seawater. Brine-rock reactions were geochemically simulated to prevent injection conditions that could cause formation damage. Additionally, pH, electrical conductivity and total dissolved solid (TDS) were analyzed in the effluents. Results show that for the model rock used, brine composition does not change significantly from contact with rock surfaces. Since wettability alteration was minimized by use of low-temperature and short ageing time, recovery correlates better with changes in interfacial rheology. For results showing an apparent lack of correspondence with the interfacial rheological response, arguments based on ganglia dynamics might shed light on the observed recovery outcome.
Our findings reveal that the injection of water with sulfate can modify the fluid-fluid interactions and consequently the final oil recovery, so in some cases, low-salinity brine injection is not necessarily conducive to an increment in oil production. Findings also indicate that more characterization of the brine-crude oil interface should be carefully conducted as part of the screening of adjusted brine chemistry waterflooding.
Use of foams to control CO2 floods conformance is attracting a renewed interest in recent years due its flexibility and ease of application. This application becomes even more attractive in current times of low oil price, as it can be an inexpensive mean to maximize CO2 utilization efficiency and increase production at no capital expenses. However, it is generally recognized that to maximize chances of success of a pilot application, an appropriate foaming formulation must be designed for a given reservoir and characterized in petrophysics lab. This usually requires an extensive laboratory work that is not always compatible with cost constraints.
We present a new cost-effective workflow that focuses on evaluating two formulation performance indicators derived from the population balance model: foam creation (related to foaming power) and resistance to foam destruction (related to foam stabilization against coarsening and coalescence).
We assess these two parameters in representative reservoir conditions by measuring foam mobility reduction in porous media and foam lifetimes. Experimental results and simple scaling arguments show that these two measurements, both of importance to the application, are mostly independent. This shed light on a recurring question pertaining to the relevance of bulk foam experiments to predict foam efficiency in porous media. With this in mind, we present a new approach for measuring mobility reduction in porous media with a higher throughput than usual corefloods experiments. This methodology is based on sandpack experiments as well as serial coreflood experiments that allow multiple successive formulations testing. We show that the link between sandpack and coreflood results is far from being straightforward, and depends on static (geometrical) as well as dynamic (flow) parameters.
Overall, this work provides new insights on the major performance indicators used to evaluate foam efficiency for gas conformance control in oil reservoirs. We build on this understanding to present a novel approach that can help developing more efficient foam EOR solutions. In particular, it allows tailoring foaming agents properties (such as foaminess and foam stabilization) to specific conditions of a given application (oil saturation, vertical heterogeneity, etc…).
Wettability of the rock is an important parameter in determining oil recovery. It determines the fluid behavior and the fluid distribution in the reservoir. Aging of the rock changes the wettability of the rock and can affect the residual oil saturation. This paper investigates the effect of aging on the oil recovery during the Water-Alternating-CO2 injection (WACO2) process using 20 in. outcrop Grey Berea sandstone cores under immiscible conditions.
In the present work, two coreflood experiments were performed. Both cores were aged for a period of 30 days at 149°F. This study is a continued research and compares the performance of WACO2 injection in aged cores to previously published work with unaged cores. All experiments were done at 500 psi and in the secondary recovery mode. The wettability of the Rock- Brine-CO2-Oil system for aged cores was determined by contact angle measurements using formation brine (174,156 ppm), seawater brine (54,680 ppm) and low-salinity brine (5,000 ppm NaCl). The interfacial tension (IFT) of the Brine-Oil-N2 and Brine-Oil-CO2 system was also measured using the axisymmetric drop shape analysis (ADSA) method. Computerized tomography (CT) scans were obtained for each core in its various states: dry state, 100% water-saturated state, oil saturated state with irreducible water saturation, and residual oil-saturated state. The CT scans were used to determine the porosity profile of the cores.
The contact angle measurements of the Rock - Brine - CO2 - Oil system indicated an increase in contact angles after the aging of the cores. Low-salinity brine showed the most water-wet state (55°) and seawater brine showed the most oil-wet state (96°) of the rock. This may be because of the increased concentration of divalent ions on the surface of the rock during seawater brine injection. Ion binding is the dominant mechanism in the oil-wet nature of the rock. The previously published work stated that the coreflood experiments of the unaged cores resulted in an oil recovery of 61.7 and 64.6% OOIP during low-salinity water-alternating-CO2 and seawater-alternating-CO2 injection, respectively. In aged cores, the oil recovery increased to 97.7 and 76.1% OOIP during the low-salinity water-alternating-CO2 and seawater-alternating-CO2 injection, respectively. The improved oil recovery was attributed to the wettability alteration when the rock was aged.
The interfacial tension measurements of brine/oil/nitrogen and brine/oil/CO2 systems showed that the salinity of the brine had an effect on the IFT. Low-salinity brine (5,000 ppm) yielded the highest IFT values and seawater brine produced the least. Monovalent ions had a weak effect on the interfacial activity between the oil and the brine. When multivalent ions were present, the IFT values were influenced by the salting effect of the brines. During the IFT measurements of brine/oil/CO2 system, the IFT values showed an increasing trend as a function of time and then stabilized. The increase in IFT was because of the initial mass transfer between the CO2, brine, and oil phases.
Low-salinity waterflooding has been portrayed as an effective enhanced-oil recovery technology. Despite compelling laboratory and field evidence of its potential, the underlying mechanisms still remain controversial. In this study, the enhanced-oil recovery mechanisms are investigated considering a distinct interfacial effect, i.e. water-crude oil interfacial viscoelasticity, through analysis of capillary hysteresis. An experimental setup with an oil-wet and a water-wet media on each end face of the core sample was utilized to capture capillary and rock electrical properties hysteresis. Moreover, new improvements over the traditional quasi-static porous plate method were implemented to accelerate measurements. Two experiments were conducted on Minnelusa formation rock samples and TC crude oil, at low temperature (30 °C) and without any significant aging as to minimize wettability alteration. Two core plugs were flooded with high-salinity and low-salinity brines, separately. It is found that the dynamic-static method with a ceramic disk, i.e. a combination of continuous injection in drainage and stepwise quasi-static method in imbibition on short 1" long core samples, allows one to capture the correct envelopes of the capillary pressure curves and save ~ 30% of the total time; a thin membrane is anticipated to save ~90% with respect to traditional quasi-static porous plate method. The capillary hysteresis experiments at low temperature prove that low-salinity brine is able to suppress capillary hysteresis. This is attributed to the formation of a more visco-elastic brine-crude oil interface upon exposure to low-salinity brine, leading to a more continuous oil phase. In addition, we show that wettability plays an essential role on electrical resistivity and the more oil-wet, the more hysteresis occurs, namely that resistivity values in imbibition are higher than those in drainage. The findings in this paper demonstrate that low-salinity waterflooding can still increase oil recovery even in the absence of wettability alteration.