Influence of ageing of rock in contact with oil on the wettability

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Experimental Study

In this chapter, we describe the materials and fluids chosen for carrying out the experiments, as well as the experimental setup and procedures followed during this work.

Porous media

The experiments were performed with 2 types of sandstones with different permeability. We chose these sandstones for their well-known mineralogy and homogeneous structure. Bentheimer is a high permeable porous medium with the permeability of 2.5-3 Darcy, while Berea is an intermediate permeable porous medium with the permeability of 80-120 mDarcy. Both porous media have a porosity of around 25%. The specific surface area for Bentheimer is0.45m²/g (Peksa et al. 2015), and for Berea is in the range of0.8-1.2m²/g (Churcher et al. 1991).
These sandstones are considered ideal sedimentary rocks for reservoir studies due to their lateral continuity and homogeneous block-scale nature. They have a uniform grain size distribution, porosity, permeability, and dielectric properties, which makes them suitable for standard laboratory experiments and associated comparison with theory [Klein and Reuschle, 2003; Ruedrich and Siegesmund, 2007]. Therefore, Bentheimer and Berea sandstones are used to investigate a variety of reservoir topics ranging from passive and active properties of oil recovery processes to flow and transport in the groundwater zone and environmental remediation processes.
The mineral composition given in the table above can vary depending on where they have been extracted and the reservoir conditions. Different researchers report slightly different values of aluminum, iron, and other minerals, but quartz content is always around 90% and higher content of clay in Berea sandstones.
The sandstones samples used in our study were rectangular and cylindrical forms with a length in range of 15 to 20 cm and with cross section in range of 16 to 19.6 cm² (Figure 2-1).
Before core flood experiments the porous media are prepared in the following way:
• Weigh the core
• Put the core between the two metallic plates that are covered by a thin layer of
Teflon™ to avoid ionic exchange between metallic plates and flowing fluids
(especially with iron which causes the degradation of polymer solution); These metallic plates have an inlet/outlet for injection/recovery of fluids and pressure tabs to measure the total pressure drop by means of differential pressure transducers
Figure 2-2. Metallic plates with cross channels used to homogenize the fluid injection.
• Cover laterally the sandstone with epoxy paste (Araldite, epoxy resin), and leave it to dry for a night
• Check the porous media for leakage with nitrogen and leak finder foam
• Drill the holes (for connections) on epoxy paste that is covering the sandstone
• Put the connections and seal the joints with epoxy paste, leave it to dry for one more night
• For mechanical rigidity purpose and safe use, cover it with fiberglass and resin, leave it to dry for another night
• Put all valves and weigh it
• It is ready for saturation
As you can see in Figure 2-3 there are 5 pressure taps to measure the pressure drop across the total length of porous media, and across sections in the internal part of it to follow the propagation of injected fluids.

Brine

The brine is a Synthetic Sea Water (SSW) which composition is presented in Table 2-2. We dissolved the salts in deionized water, then filtrated under low pressure through 0.45µm polycarbonate filter and degassed under gentle stirring and low pressure. The KI was added to serve as a tracer only for dispersion test experiments. As we can see, the ratio of divalent/monovalent salt content is about 2:1

Polymer

The polymers provided by SNF Floerger were available considering different hydrolysis degree, molecular weight, chemical composition, and molecular structure. For our study we have chosen the polymers that vary by molecular weight, (high and low), and chemical structures (with or without ATBS, that will infer ionic characteristics to the polymer in solution state). Table 2-3 summarizes the different polymers available and those used in this study (framed ones).
To investigate the influence of molecular weight on polymer adsorption/retention in porous media we used polymers Flopaam 3630S and 3130S with a molecular weight of 19MDa and 3MDa respectively. These are hydrolyzed polyacrylamides HPAM with a 30% hydrolysis degree. We also performed experiments with sulfonated HPAM polymers Flopaam 5115 XV and 5115 BPM with a molecular weight of 19MDa and 3MDa respectively. Both polymers have a hydrolysis degree of 10%, and a sulfonation degree of 15%. All polymers that were provided by SNF Floerger were in dry white powder form of various moisture content.
The amount of moisture in polymer powder was measured using an infrared balance to have pure polymer mass and prepare the right concentration of polymer.

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Polymer solution

All polymer solutions were prepared by diluting a concentrated mother solution that is prepared beforehand according to the following procedure:
1. Pour 500ml of brine into a beaker
2. Place a stirring rod in the beaker. It should be placed in the middle of the beaker and as low as possible. Set rotor speed at 500 rpm to create a vortex
3. Pour the polymer powder gently into the vortex shoulder. It is recommended to do it grain by grain to ease the powder dispersion
4. Leave the solution under stirring for 2h
5. Decrease the stirring rate to ≈150 rpm, cover it with a plastic film and leave it for a night
6. Filter the mother polymer solution through polycarbonate filters in series: 10, 5, and 2 µm at constant flow rate 0.3ml/min using a volumetric pump
7. Keep the stock solution under nitrogen gas in a fridge. It is to be mentioned that 400ppm of were added to SSW in this case. Doing so, polymer was protected against oxidation, bacterial and chemical degradation.
To prepare the daughter solution, this mother solution was diluted with SSW.
The shear viscosity of each polymer solution was measured using a controlled shear stress rheometer ARG2 (TA Instruments, France) or Kinexus (Malverne, France). We measured viscosity at temperature T=25°C using a 2° cone/plate geometry by steeply increasing shear rate from to . For very low viscous polymer solutions we used Ostwald viscometer.

Table of contents :

1. Introduction
1. Chapter I : General features & literature review
1.1. Porous media
1.2. Flow in porous media
1.2.1. Pore scale
1.2.2. Local scale
1.3. Miscible flows
1.3.1. Molecular diffusion
1.3.2. Dispersion
1.4. Diphasic flows
1.4.1. Concept of saturation
1.5. Interfacial tension and wettability
1.5.1. Wettability measurement
1.5.2. Influence of ageing of rock in contact with oil on the wettability
1.5.3. Generalized Darcy’s model
1.5.4. Capillary pressure
1.5.5. Relative permeability hysteresis
1.5.6. Parameters that influence wettability
1.5.7. Wettability of porous media
1.6. Polymer
1.6.1. Conformation of polymers in solution state
1.6.2. Entanglement concentration
1.6.3. Viscosity of polymer solutions
1.7. Polymer at the surface
1.7.1. Adsorption from quiescent solution
1.8. Polymer solution in Porous medium
1.8.1. Mechanical entrapment
1.8.2. Hydrodynamic retention
1.8.3. Polymer adsorption
2. Chapter II: Experimental Study
2.1. Porous media
2.2. Brine
2.3. Polymer
2.3.1. Polymer solution
2.4. Experimental setup
2.5. Experimental equipment
2.5.1. Pressure transducers
2.5.2. Pumps
2.5.3. Spectrophotometer
2.5.4. TOC-L/TNM-L
2.6. Experimental procedure
2.6.1. Characterization of porous media
2.6.2. Monophasic experimental procedure
2.6.3. Diphasic experimental procedure
3 Chapter III – Results and Discussion
3.1 Composition of brine
3.2 Viscosity of polymer solutions
3.2.1 Influence of concentration on viscosity
3.3 Characterization of porous media
3.3.1 Porosity, pore volume and homogeneity of PM
3.3.2 Permeability
3.4 Monophasic experiments
3.4.1 Polymer flooding
3.4.2 Mobility reduction
3.4.3 Brine flush
3.4.4 Permeability reduction
3.4.5 Second polymer flooding
3.4.6 The retention of polymer
3.4.7 Inaccessible pore volume
3.5 Diphasic experiments: Water-wet condition
3.5.1 Oil drainage
3.5.2 Waterflooding
3.5.3 Dispersion test in diphasic
3.5.4 Polymer flooding
3.5.5 Mobility reduction
3.5.6 Brine flush and permeability reduction
3.5.7 Second polymer injection
3.5.8 Retention of polymer
3.5.9 IPV
3.6 Diphasic experiments: Altered wettability porous media
3.6.1 Permeability to oil after ageing
3.6.2 Waterflooding
3.6.3 Polymer flooding
3.6.4 Retention of polymer
4. Chapter IV: Conclusions and perspectives
5. Nomenclature
6. Bibliography
7. Appendix A
8. Appendix B

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