Coherence with the call topic

The project fits well the full scope of the „Environment” research priority of the Polish-Norwegian Research programme. It is focused on research within the scope of innovative technology, allowing for an efficient development of conventional and unconventional gas reservoirs, combined with maximum reduction of the negative impact of this process on the natural environment. The detailed thematic priorities are closely connected with the research object:

• rational use of natural resources, including rational water management – energized fluids allows for more efficient usage of gas resources, with minimized amounts of water for fracturing.
• recycling technologies - CO2 comes from capturing processes, Because CO2 flows out of the well as a gas, even if mixed with water, there is less water to recover. Excessive water flowback leads to more costs of reuse, or disposal.
• technologies of new and renewable energy sources - development of unconventional gas and oil resources can provide new energy sources for Europe.
• technologies that impact limiting of greenhouse gases and aerosols - application of CO2 for fracturing unconventional formations minimizes atmospheric emissions only to a minor extent but enabling usage of unconventional gas instead of the coal is key for CO2 and particulates emissions abatement in Central Europe.
• technologies of carbon capture and storage (CCS) - CO2 geological storage efficiency (eg. injectivity of a formation) - may depend on fracturing jobs, which are enhanced by application of energized fluids, which are intended to be developed and tested in different conditions within this project.

Current state of the art including your relevant previous work

Injection of CO2 – based energized fluids may also enhance hydrocarbons recovery from a well, allowing for carbon dioxide storage in the geologic formation at the same time The energized fracturing fluid (in the form of foam should be a stable mixture of liquid and gas. In order to produce such stable mixtures surfactants are applied, that concentrate at the he gas/liquid interface and reduce the surface tension between the phases. The surfactant stabilizes the thin liquid film and prevents the merging of bubbles of gas.

Compressed gas (nitrogen or carbon dioxide) in the foam is expanding during the backflow of the treatment fluid (EFF) by facilitating the removal of liquid from the fracture. EFF foams accelerate removal of liquid from the propped fracture and therefore they are excellent fracturing fluids for use in low pressure reservoirs. Also, the amount of liquid phase is minimal because the foam contains up to 95%vol. of gas. In the case of water-based fluids, their foaming significantly decreases the amount of liquid that is in contact with the reservoir formation. Therefore, the EFF foam is also recommended in the case of reservoir rocks that are particularly water-sensitive (eg. swelling clay).

Improvement of the EFF stability can be achieved by crosslinking the added polymer. The liquid phase is then sufficiently viscous to maintain a dispersion of gas bubbles. Increasing the viscosity of the liquid phase results in an improvement of foam rheology and filtration control. The gas bubbles are generated by the turbulent flow, that occurs during the mixing of liquid and gas. Bubbles form in the liquid emulsified foam disappearing slowly with time. Inside the fracture, under high pressure, the foam half-life is significantly longer than measured under atmospheric pressure.

CO2 has a higher density than nitrogen therefore it is able to produce Energized fracturing fluids of higher density. This results in higher hydrostatic pressures in the wellbore during pumping of a fluid, which results in smaller values of the surface pressure. With lower pressures during the treatment it is possible to reduce pumping costs.

The CO2 energized fracturing fluid is heated, when it is injected into the reservoir formation of the temperature above the critical value, and the carbon dioxide passes from the liquid to the gaseous and the foam is being formed. The structure of the foam produced using CO2 is similar to that obtained with the involvement of nitrogen, but the proppant carrying capacity of the first one is greater than in the case of the nitrogen foam. On the other hand, the CO2 foam have a higher flow resistance than nitrogen-based foam, particularly for those heavily loaded with proppant.

Although CO2 is a valuable and widely used EOR process, several studies have shown that CO2 mayinduce asphaltene precipitation. Werner et al., (1996) reportes that the CO2 injection is a main factor for asphaltene precipitation. Asphaltene deposition is initiated by CO2 when the critical content of CO2 is exceeded. The critical content point of CO2 is dependent on oil composition, temperature and pressure and must be evaluated at early stage of screening methods for EOR (Chukwudeme and Hamouda,2009).

During the fracturing a good filtration control is necessary in order to create a suitable geometry of the fracture and provide the transport of proppant. At the beginning of the fracturing it is dependent on the permeability of the formation. Also, the foams generated on the basis of the gelled fracturing fluids, enable the filter cake formation on the fracture walls. It is thinner that in the case of one-phase fluids, and still the filtration is usually lower. This is due to the penetration of the gas bubbles to the pores, which inhibits the escape of liquid from the fracture. Therefore, the two-phase flow through a porous medium is lower than for a single phase liquid. Because of these properties of the foams produced from energized fluids, that contain a linear gel, in effect of fracturing it is possible to achieve the matrix permeability in the nearfracture zone equal to about 95% of the initial permeability. Also the permeability damage of the proppant material filling the fracture, by such a treatment fluid, is much lower.

Foams from energized fracturing fluids are characterized using several rheological models including Herschel-Bulkley model, Bingham and by a wide range of experimental methods. For foams generated using the nitrogen all the typical combinations of polymer – crosslinker can be used. This is since nitrogen is inert and does not interact chemically with the crosslinking agent. In the case of foams produced with CO2 the fact should be taken into account, that the crosslinking process must take place in an environment with a pH between 3 and 5, which is due to the acidifying effect of CO2 on the outer liquid phase.

Typically hydraulic fracturing flowback waters contain suspended particles along with low molecular weight organic and inorganic contaminants that need to be separated before fluid reuse or its discharge into environment. They are typically treated using chemical, thermal and membrane methods. Applied technological scheme depends on flowback composition. Chemical treatment includes metals precipitation and filtration. Pretreated waters undergo dilution using municipal drinking water with recycle back to well sites or (more often) concentration by nanofiltration, reverse osmosis and/or thermal evaporation to recover part of water and decrease the volume of discharge. We have experience width chemical treatment of wastewaters including coagulation, photocatalysis, organic compound reduction, and membrane methods including electrodialysis and electrodialysis reversal ED(R), ultrafiltration, nanofiltration (NF), and reverse osmosis. In our opinion pretreated flowbaks should be treated with methods resistant for fouling and scaling. Developed by us ED(R) and NF modules are less susceptible for fouling and scaling than commercial ones and are especially suitable to work in the mode of high supersaturation with sparingly soluble salts as well as organics. This mode of operation, with controlled crystallization outside the module, enables zero discharges technology to develop.

Description of the Project Plan

Samples representing reservoir rocks from Central Europe will be selected and examined for their petrophysical properties and petrographical composition in WP1. Geochemical research (including material maturity and organic matter type will be performed as well. These results will allow to develope the screening criteria for the CO2 enhanced oil recovery for the reservoirs considered. After fracturing performed on all samples the petrographical analysis will be performed for visualization of created fracture system.

In the WP2 original fracturing fluid systems for use in reservoir conditions of Central Europe will be prepared and evaluated. Their physical properties and the proppant damage in the fracture caused by fracturing fluid and leak-off tests under dynamic and static conditions are intended to be tested.

The interactions between energized fluids and formation rocks will be examined and characterized based on coupled experiments and kinetic modeling of fluid-rock-gas reactions for the reservoir rocks in WP3. Geochemical models, enable to determine the impact of energized fluids on the mineralogical composition and petrophysical parameters of rocks. The method of predicting geochemical effects of fracturing will be elaborated on this bases.

In WP4 the CO2/liquid/formation interaction will be addressed including development of methods of research on the CO2/liquid/formation interactions and study of mutual interactions in the systems gas-liquid-rock controlling the stability of energized fracturing fluids and influencing the permeability of the formation.

The WP5 is aimed to evaluate formation damage caused by fracturing fluids proposed in WP2. In order to predict the effects of these phenomena a study on the impact of the developed fluids on clay minerals present in the reservoir rocks will be performed. To determine formation damage of consolidated unconventional rocks a prototype apparatus will be developed.

The main objective of WP6 is to propose a treatment method for reuse and utilization of flowbacks produced with use of energized fracturing fluids. The most important action within the package will be experimental evaluation of the eficiency of the methods of separation of the key and most troublemaking contaminants. This will allow minimizing the environmental impact of the fracturing process that should have an effect on social concern with respect to the fracturing with energized fracturing fluids.