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.
The use of isenthalpic flash has become of interest for the simulation of some heavy oil recovery processes where large temperature changes are experienced. For these thermal simulations energy can be used as a primary variable. This leads to thousands or millions of individual multiphase isenthalpic flash calculations. Robust and efficient algorithms for multiple-phase isenthalpic flash are required to improve the efficiency of compositional simulations for thermal recovery.
The general framework on state function based flash specifications proposed by
Narrow boiling mixtures can be dealt with in the majority of cases without any significant difficulty. This is true of the direct substitution algorithm and the proposed solution procedure. The vast majority of examples can be solved without using Q function maximisation. The challenges associated with multiphase calculations in the Newton steps are investigated. In particular, inadequate initial estimate of the equilibrium type may lead to non-convergent iteration. This can usually be solved by introduction of a new phase and/or elimination of an existing phase. The speed of the method is analysed for a large number of specifications and is found to be only slightly more expensive than isothermal flash in the majority of cases.
Polymer flooding can significantly improve sweep and delay breakthrough of injected water, thereby increasing oil recovery. Polymer viscosity degrades in reservoirs with high salinity brines, so it is advantageous to inject low salinity water as a preflush. Low salinity water flooding (LSW) can also improve local displacement efficiency by changing the wettability of the reservoir rock from oil wet to more water wet. The mechanism for wettability alteration for low salinity waterflooding in sandstones is not very well understood, however experiments and field studies strongly support that cation exchange (CE) reactions are the key element in wettability alteration. The complex coupled effects of CE reactions, polymer properties, and multiphase flow and transport has not been explained to date.
This paper presents the first analytical solutions for the coupled synergistic behavior of low salinity waterflooding and polymer flooding considering cation exchange reactions, wettability alteration, adsorption, inaccessible pore volume (IPV), and salinity effects on polymer viscosity. A mechanistic approach that includes the cation exchange of Ca2+, Mg2+ and Na+ is used to model the wettability alteration. The aqueous phase viscosity is a function of polymer and salt concentrations. Then, the coupled multiphase flow and reactive transport model is decoupled into three simpler sub-problems, one where cation exchange reactions are solved, the second where a variable polymer concentration can be added to the reaction path and the third where fractional flows can be mapped onto the fixed cation and polymer concentration paths. The solutions are used to develop a front tracking algorithm, which can solve the slug injection problem where low salinity water is injected as a preflush followed by polymer. The results are verified with experimental data and PennSim, a general purpose compositional simulator.
The analytical solutions show that decoupling allows for estimation of key modeling parameters from experimental data, without considering the chemical reactions. Recovery can be significantly enhanced by a low salinity pre-flush prior to polymer injection. For the cases studied, the improved oil recovery (IOR) for a chemically tuned LSP flood can be as much as 10% OOIP greater than with considering polymer alone. The results show the structure of the solutions, and in particular the velocity of multiple shocks that develop. These shocks can interact, changing recovery. For example, poor recoveries obtained in core floods for small low salinity slug sizes are explained with intersection of shocks without considering mixing. The solutions can also be used to benchmark numerical solutions and for experimental design. We demonstrate the potential of LSP as a cheaper and more effective way for performing polymer flooding when the reservoir wettability can be altered using chemically-tuned low salinity brine.
Barnes, J. R (Shell Global Solutions International B.V.) | Regalado, D. Perez (Shell Global Solutions International B.V.) | Doll, M. J. (Shell Global Solutions (US) Inc.) | King, T. E. (Shell Global Solutions (US) Inc.) | Pretzer, L. E. (Shell Global Solutions (US) Inc.) | Semple, T. C. (Shell Global Solutions (US) Inc.)
Surfactant flooding is an enhanced oil recovery (EOR) technique that involves the injection of an aqueous solution of surfactant (and, optionally, alkaline and polymer) into an oil reservoir to mobilise and produce the remaining oil. The quantities of surfactants needed for pilots and future commercial scale projects are large (100s to 10,000s of tons) and necessitate large scale manufacture using existing processes and plants for the different manufacturing steps. Upscaling of surfactants requires a rigorous QA/QC process to control and ensure the quality of batches of surfactants produced. Case studies are described from the perspective of a surfactant manufacturer where 800 and 6000 ton of surfactant were manufactured (as 60% and 20% active concentrates respectively) for two multi spot pilots. These case studies illustrate: The need to define the laboratory tests for surfactant composition and performance. Plus associated repeatability data and specifications (minimum and maximum values) for clear, unambiguous decisions. How the QC is checked at each stage in manufacture from the initial feedstock, through various stages, to the final delivered surfactant concentrate/blend. This also applies to the scale-up procedure from the laboratory made scale (kg) to pilot scale (100s of kg) to the pilot/commercial scale (100s to 1000s of tons). Novel correlations between composition and performance (e.g. optimal salinity, via oil/water phase behaviour tests), developed during the surfactant pilot scale manufacture stage, to a) put more emphasis on verifying batch consistency with faster, easier to use composition tests, and b) give more assurance that large scale production gives the expected sub-surface performance. This requires R&D over an extended time, ahead of large scale manufacture.
The need to define the laboratory tests for surfactant composition and performance. Plus associated repeatability data and specifications (minimum and maximum values) for clear, unambiguous decisions.
How the QC is checked at each stage in manufacture from the initial feedstock, through various stages, to the final delivered surfactant concentrate/blend. This also applies to the scale-up procedure from the laboratory made scale (kg) to pilot scale (100s of kg) to the pilot/commercial scale (100s to 1000s of tons).
Novel correlations between composition and performance (e.g. optimal salinity, via oil/water phase behaviour tests), developed during the surfactant pilot scale manufacture stage, to a) put more emphasis on verifying batch consistency with faster, easier to use composition tests, and b) give more assurance that large scale production gives the expected sub-surface performance. This requires R&D over an extended time, ahead of large scale manufacture.
Overall, the paper shows that industrial scale production of surfactants for chemical EOR is feasible and goes through the essential steps to achieve this. Control of large scale batch quality and performance is critical.
This paper also shows results for improved, highly active (60%+) surfactants concentrates with improved rheology behaviour which will be easier to pump, mix and dilute at the facilities than earlier products. This helps to reduce logistical costs thereby improving project economics.
Khorsandi, Saeid (The Pennsylvania State University) | Qiao, Changhe (The Pennsylvania State University) | Johns, Russell T. (The Pennsylvania State University) | Torrealba, Victor A. (The Pennsylvania State University)
Reservoir simulation is a valuable tool for assessing the potential success of enhanced recovery processes. Current chemical flooding reservoir simulators, however, use Hand's model to describe surfactant-oil-brine systems even though Hand's model is not predictive, and can fit only a limited data set. Hand's model requires the tuning of multiple empirical parameters using experimental data that usually consist of salinity scans at constant reservoir temperature and atmospheric pressure. Given experimental data supporting the change in microemulsion phase behavior with key formulation properties (e.g. temperature, pressure, salinity, EACN, and overall composition), there is a need for an improved model that can capture changes in these relevant parameters at the reservoir scale. The recent EOS proposed for microemulsion phase behavior (
In this paper, the EOS model with the extension to two-phase regions is incorporated for the first time into the chemical flooding simulators, UTCHEM, and our new in-house simulator PennSim. Hand's model is only used for comparison purposes, and is no longer needed even for flash calculations in the type II- and type II+ regions. The results show excellent agreement between UTCHEM and PennSim both in composition space and for composition/saturation profiles. Further, the HLD-NAC based EOS model and Hand's models are fitted to the same experimental data and the results of these simulations are nearly identical when variations of salinity, pressure and temperature are small. For large gradients, the results of the physics-based EOS deviates from Hand's model, and shows it is critical to incorporate these gradients in recovery predictions at large scale.
Scaling up from lab to pilot is one of the challenges to meet in any ASP project to accomplish the requirements at full implementation. Tailored EOR surfactants developed and manufactured in the laboratory, to achieve the lowest interfacial tension (IFT) between oil and water at the reservoir conditions, have to be viable and robust in the manufacture, capable in performance and compatible in the formulation, not only at laboratory scale, but also at industrial scale.
It is described in this poster the route map in the development and manufacture of alkyl aryl sulfonates surfactants for the Cepsa ASP pilot project in the Caracara Sur field, Los Llanos basin (Colombia) from a continuous feed-back of the laboratory tests. The surfactant employed for the project was selected from other surfactants from several suppliers and dyalkylbenzene sodium sulfonate was the one achieving the lowest interfacial tension for Caracara field conditions. The dyalkylbenzene sodium sulfonate was accompanied by a co-surfactant improving the solubility and performance properties.
Pilot ASP injection started in May 2015 and some conclusions were obtained during the production of the surfactants in several manufacture batches: Composition, molecular weight even isomerism of alkylbenzenes may impact strongly on the interfacial activity of alkyl aryl sulfonates surfactants. Sulfonation and neutralization of alkylbenzenes are critical processes to comply the requirements of alkyl aryl surfactants for any cEOR project. Finally, the laboratory in the field for quality assurance and quality control (QA/QC) of surfactants is completely necessary. Periodical sampling and on-site analyses are scheduled but also samples delivery to research center for more sophisticated analyses. These data are essential for the final performance evaluation and the project success.
Composition, molecular weight even isomerism of alkylbenzenes may impact strongly on the interfacial activity of alkyl aryl sulfonates surfactants.
Sulfonation and neutralization of alkylbenzenes are critical processes to comply the requirements of alkyl aryl surfactants for any cEOR project.
Finally, the laboratory in the field for quality assurance and quality control (QA/QC) of surfactants is completely necessary. Periodical sampling and on-site analyses are scheduled but also samples delivery to research center for more sophisticated analyses. These data are essential for the final performance evaluation and the project success.
Piñerez T., Iván D. (University of Stavanger) | Austad, Tor (University of Stavanger) | Strand, Skule (University of Stavanger) | Puntervold, Tina (University of Stavanger) | Wrobel, Stanislaw (University of Stavanger) | Hamon, Gérald (Total E&P)
Low salinity water injection in sandstone is an emerging technology just on the verge of being implemented full field in the UK and in Alaska, USA. Laboratory studies are important for providing relevant and well interpreted data before performing the field trial. However, laboratory investigations show varying results on low salinity EOR, most probably because of a limited understanding of the nature of the process. Recently we have published a "Smart Water" EOR mechanism where pH changes at the rock surface is inducing the wettability alteration, improving positive capillary forces and microscopic sweep efficiency. Researchers have experienced rather poor low salinity EOR effects from 17 different sandstone outcrops from the USA.
In this work we have investigated 6 of the same 17 outcrops, and according to our chemical understanding, some factors are more important for observing LS EOR effects in sandstone. It is the increase in pH, ?pH, obtained when the high salinity (HS) formation water is displaced by the low salinity (LS) injection water, and it is the initial pH and the amount of active cations (Ca2+) in the formation water that are related to the initial wetting.
We have established a link between the poor low salinity EOR effect from all 6 outcrops and the corresponding pH change observed when switching from high salinity to low salinity injection water. The presence of different types of minerals such as clay, feldspars and anhydrite will influence the pH change, and must be taken into account. Additionally, we have seen that the formation water composition has strong influence on the low salinity EOR effect. Using a formation water with salinity like seawater (FW1 ~35 000 ppm) showed only a minor tertiary low salinity EOR effect, 0.74 %OOIP, corresponding to a low pH gradient of 0.5. While experiments using a high salinity formation water (FW2 ~100 000 ppm) showed a 5 % OOIP recovery, corresponding to a larger pH gradient of 2.0.
The results observed are in agreement with the suggested chemical mechanism for the low salinity EOR effect, confirming that it is the pH gradient that triggers the low salinity EOR effect. In addition, the pH screening test used in this work proved once again to be a reliable tool to evaluate the low salinity EOR potential.