Development of Nanoparticle-Stabilized Foams To Improve Performance of Water-less Hydraulic Fracturing
Last Reviewed Dated
The project goal is to develop a new method of stabilizing foams for frac fluids by adding surface-treated nanoparticles and/or surfactants to the liquid phase. The research will use commercially available or in-lab-modified nanoparticles and surfactants. The fracturing fluids will be those already employed in hydraulic fracturing: carbon dioxide [CO2], nitrogen [N2], and water.
The University of Texas at Austin, Austin, TX, 78712-0228
The rapid development of hydraulically fractured unconventional oil and gas reservoirs had made significant demands on water resources. A decisive advantage of foamed fluids is that they use substantially less water. Foamed fluids have been used to improve flowback and cleanup after treatment, to improve stimulation performance by reducing leakoff rates, and to reduce fluid blocking of hydrocarbon production from the reservoir. Nanoparticles with suitable surface coatings have several advantages specific to the application of foamed-fracturing fluids: they can stabilize viscous foams very for long periods to carry proppant; they are much smaller than pores in proppant packs, which allows them to be transported out of the reservoir during flowback; and their coating and concentration can be tuned to different fluid/fluid systems. Nanoparticles enable a potentially significant advance: foams can be generated that will carry proppant into a fracture but will break at a tunable threshold pressure after the stage is pumped and will not re-form in the proppant pack during flowback. Whereas foam (energized) fluids typically use about 20 to 40% water, the research team has introduced ultra dry CO2 and nitrogen foams with as little as 2 to 5% water by stabilizing the foams with nanoparticles and/or surfactants that viscosify the aqueous phase. Not only does the use of these energized fluids reduce water utilization and disposal, but it minimizes fluid blocking of hydrocarbon production.
This project seeks to demonstrate that suitably coated nanoparticles or viscoelastic surfactants can stabilize foams of fluids useful for hydraulic fracturing at elevated pressures and at temperatures ranging from ambient to reservoir conditions. The water-based foams require four to twenty times less water per barrel of fluid than conventional water-based fracturing fluids. Thus, this research would have a significant impact on the development of unconventional oil and gas resources in areas where water use and/or disposal is constrained.
The results of this research will expand the options available to operators for hydraulic fracturing and can simplify the design and field implementation of foamed frac fluids. The technology will make it easier for operators to switch to reduced-water or zero-water hydraulic fracturing campaigns, thereby alleviating one of the most sensitive challenges for domestic hydrocarbon production.
Accomplishments (most recent listed first)
A model of fracture propogation and cleanup indicates larger foam viscosity for dry CO2 foams generate wider fractures with smaller fracture length and less leak off. The model combines gas and water flow in the matrix and fracture, fracture geometry and mechanistic accounting of foam generation and coalescence (population balance). The dry foams leave little residue in the fracturing zone and the low water amount causes less pore blockage resulting in improved oil and gas production rates. Finally, CO2foams have been tested in the lab (in a high pressure sapphire cell) and are able to carry sand particles without destabilization for over 24 hours.
Novel surface-modified silica nanoparticles have been synthesized and shown to be colloidally stable in API brine and also active for stabilizing CO2 and nitrogen foams when combined with various zwitterionic carbobetaine surfactants. A synergistic effect has been discovered in which only 0.2% nanoparticles and 0.02 to 0.2% surfactant in the aqueous phase stabilize viscous foams with sub-100 μm bubbles, whereas neither the nanoparticles nor the surfactant alone are effective.
Nanoparticle/surfactant stabilized CO2 foams have been extended up to 90ºC in API brine with newly synthesized anionic silica nanparticles with high salt tolerance. These systems exhibit synergy in foam stabilization found at lower temperatures and thus require less than 1% nanoparticles and surfactant.
Nitrogen foam with viscoelastic aqueous phase lamellae have been generated and stabilized at 25ºC and 90ºC, and the role of the foam generator (beadpack) permeability has been determined for 1.8 to 22 Darcy beadpacks. The apparent foam viscosities are >300 cP at 0.95 quality with bubble sizes down to ~ 5 μm.
Ultra-dry foams have been stabilized with environmentally benign carbobetaine zwitterionic surfactants.
A mechanistic understanding of the stabilization of ultra dry foams has been developed by determining the interfacial and rheological properties of the foam along with the foam bubble size and the change in bubble size with time. This mechanistic insight has been used to transition from the use of two or more stabilizers in our earler work to only a single betaine zwitterionc surfactant to stabilize ultra dry foams by forming viscoelastic wormlike micelles.
The concentration range of surfactant ultra-dry foams with up to 98% CO2 by volume has been lowered to only 1% in the aqueous phase with single zwitterionic amidopropylcarbobetaine zwitteironic surfactants that are commercially available. The foam is stabilized for up to one day by wormlike micelles formed at low surfactant concentrations as a consequence of their long tails and weak headgroup repulsion.
The temperature range of ultra-dry foams has been extended up to 120ºC with single zwitterionic amidopropylcarbobetaine zwitteironic surfactants that are commercially available. The foams are stablilized, despite the high temperature, by the formation of wormlike micelles that slow down the drainage of the aqueous lameallae between the foam bubbles.
The ability of CO2 foams to suspend proppant has been shown with a high pressure sapphire cell for a period of one day, as expected from the apparent foam viscosity.
Micromodel expertise has been developed in the lab. Micromodels are quasi-two-dimensional porous media that unlike proppant packs, enable direct visualization (via microscope) of a phenomenon of interest (in this case foam texture and stability) in a transparent porous medium of controlled properties (pore sizes, the aspect ratio between pore and throat sizes, the level of heterogeneity, etc.). This will enable a better understanding of mechanisms of ultra-dry foam generation, break-up and potential regeneration in a much more direct way compared to proppant packs where one cannot directly observe the behavior. Foam generation with LAPB surfactant and EOR5 nanoparticles has been studied in two differnet types of micromodel designs.
The high temperature behavior of the new ultra-dry foam with wormlike micelles has been investigated. At 90°C, the apparent viscosity of CO2-in-water foams with high foam quality are shown to be as high as (>100 cP) those at room temperature. This result suggests a promising potential for the ultra-dry foam in actual hydraulic fracture reservoirs, which are usually at very high temperature.
A new type of dry foamhas been developed. High internal phase, very dry 0.95-0.98 supercritical CO2-in-water foams with fine ~20 μm polyhedral shaped bubbles, high viscosities >100 cP and long lifetimes (3 h), are demonstrated. For the driest foams at CO2 volume fraction of 0.98, the foam viscosity increased markedly by 2-3 times when stabilized with viscoelastic wormlike micelles, relative to the case of a low viscosity aqueous phase with spherical micelles. The wormlike micelles were formed by raising the packing parameter of sodium lauryl ethoxylated sulfate (SLES) with salt and protonated C10DMA, as shown by cryo-TEM, and large values of the zero-shear viscosity and the dynamic storage and loss moduli.
The fluid transport and fracture opening simulations confirmed that higher foam viscosity generated wider fractures with smaller fracture half-length. Fracture cleanup simulations have demonstrated the advantage of using dry foams. They show that fracturing fluid cleanup for foam-based fracturing fluids could take 10 days as opposed to that of a viscous fracpad which could take up to 1000 days.
The mechanisms involved in foam creation and stability have been experimentally investigated. Surfactant reduces the interfacial tension, and thus, facilitates bubble generation and decreases the capillary pressure to reduce the drainage rate of the lamellae. The lauramidopropyl betaine (LAPB) foam, which is cationic, also attracts anionic nanoparticles to the interface. The adsorbed nanoparticles at the interface are shown to form a barrier that slows down Ostwald ripening, with or without the addition of polymer, and increases foam stability.
The nanoparticle/surfactant/LAPB-stabilized foam quality has been improved up to 0.98 internal phase volume. (Note that the fracturing fluids reported in literature have CO2 fraction at most 0.75. ) For foams stabilized with mixture of LAPB and NPs, fine 70 µm bubbles and high viscosities on the order of 100 cP at >90% internal phase fraction were stabilized for hours to days. The viscosity of 90% foams is inversely proportional to the bubble size.
Nanoparticle/surfactant/polymer synergy was explored in order to increase the foam viscosity. CO2-in-Water (C/W) foams of 70 centipoise (cP) at 0.95 quality were stabilized by using 0.15 % hydrolyzed polyacrylamide (HPAM), 1% Nissan EOR-5XS nanoparticles and 0.08 % LAPB surfactants, which is comparable to typical viscosities of fracturing fluids reported in literature.
Phase behavior studies of mixtures of a series of different polymers, surface modified nanoparticles and surfactants have been further investigated to show that the formulations were stable in CO2 saturated 2% potassium chloride brine at pressures and temperatures relevant to field operation conditions (1000–5000 pounds per square inch, 50 degrees Celsius).
A simulator for nanoparticle-stabilized foam flowback after hydraulic fracturing has been developed in order to study the effect of depressurization on nanoparticle-stabilized foams. A preliminary comparison of fracture propagation with slick water, viscous fracpad, and 0.9-quality foam shows that foams leave a much cleaner proppant bed after fracturing, which can subsequently improve production from the formation.
Stable CO2-in-water foams were produced in a beadpack using mixtures of surface-modified, commercially available silica nanoparticles and three carboxybetaine surfactants. These foams have much higher viscosity than foams generated with the either the nanoparticles or surfactant alone. This synergy is a remarkable property and, to our knowledge, not previously demonstrated.
Building on this synergy between nanoparticles and a very low concentration of betaine surfactant, the project team was able to generate stable 90 percent quality CO2-in-water foams, with apparent viscosities as high as 50 cP, by adding 0.1 percent partially hydrolyzed polyacrylamide polymer. The polymer provides a second, distinct synergistic effect: foam cannot be generated until a threshold polymer concentration is reached.
Conceptual models have been developed to predict stability of bulk foams and foams in porous media under different operating and synthesis conditions with particular attention paid to the influence of pressure, which is the proposed mechanism for controlling foam destabilization for flowback after fracture stimulation.