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6.2. Experimental section 816.2.2 Core holder and fluid injection systemA custom-made core holder was designed which fitted in the insert of the NMR apparatus.The holder is made of poly-ether-ether-ketone (PEEK) and can withstand pressures up to23 bars. The temperature of the core holder was not controlled. During the experimentthe cores are oriented vertically, and the inlet is at the bottom. The fluids are injected bytwo continuous-injection pumps (P500, Amersham Bioscience) connected to a computer.The differential pressure over the core holder was monitored with a Deltabar S pressuretransducer (range: 0–1500 mbar). The tubing, between the core holder and the pressuretransducer, introduces an additional pressure loss at a given flow rate. This pressure losswas calibrated and taken into account in the permeability measurements. A schematicview of the set-up is given in Figure 6.3. For the shut-in step, during which the reactivemass transfer is monitored through the NMR measurements, the cores are taken out ofthe core holder, sealed and put in a second sample holder. In this sample holder, madeof polyvinylchloride (PVC), a fluorocarbon fluid (Galden TM HT135, manufactured bySolvay Solexis) with a regulated temperature is circulated so that the temperature of thesample can be controlled. The fluid is invisible to the NMR set-up and the temperaturecan be controlled between 10 and 65 ◦ C with an accuracy of about 1 degree.6.2.3 NMR apparatus and methodsA 0.95 Tesla NMR scanner was used to perform the NMR experiments. The scanner isequipped to measure both hydrogen, at a frequency of 40.5 MHz, as well as deuterium,at a frequency of 6.21 MHz. The set-up consists of an electromagnet with a vertical,narrow-bore insert with an inner diameter of 31 mm. A single rf coil is used with twodifferent front-end rf circuits for 1 H, respectively 2 H. Switching between the two circuits isautomated and takes less than a second, allowing for a fast sequential NMR measurementof hydrogen and deuterium. The insert is capable of producing a static magnetic gradientup to 0.2 T m −1 in the vertical direction. The position of the core holder and sampleholder is controlled by a stepper motor.The sequences used for the experiments and details about the methods were discussedin Chapter 2. T 1 of the hydrogen content in the oleic phase is measured with a saturationrecovery sequence to determine the TMOS concentration in oil, T 2 of the aqueous phaseis measured with a Carr-Purcell-Meiboom-Gill (CPMG) sequence to monitor the progressof gelation. In this case T 2 is measured for the deuterium content. A 1D static magneticgradient is used. Due to the relatively low signal to noise ratio for deuterium the signal isaveraged 64 times. The acquisition time for a T 2 measurement in a single slice is about 4minutes. The gradient strength was 0.030 T m −1 and 0.015 T m −1 for 1 H, respectively 2 H.In each experiment five equally-spaced slices were considered. The slice positions alongthe vertical direction were: -25 mm, -12.5 mm, 0 mm, 12.5 mm and 25 mm with respectto the center of the cores (see Figure 6.3). The relaxation times were acquired for eachslice by using and averaging the part of the signal profile corresponding to a thickness of3.1 mm. The saturation recovery data were analyzed and fitted with mono-exponentialdecay functions yielding the relaxation times T 1 . The CPMG data were analyzed withthe inversion routine CONTIN [66] to give quasi-continuous T 2 spectra, consisting of one
82 6. Coupled mass transfer and gelation of TMOS in porous materialsTable 6.1: Fluid injection steps in the core experiments.step description final saturation permeabilityparametermain procedure:1 water injection S w = 1 K abs2 primary drainage (oil) S w = S wi k ro3 secondary imbibition (water) S w = 1 − S or k rw4 secondary drainage (oil) S w = S wi k ro5a TMOS/oil injection S w = S wi ′ -5b shut-in6 oil injection S w = Swi ∗ kro∗7 water injection S w = 1 − S or krw∗alternative procedure:1 oil injection S o = 1 K abs2 TMOS/oil injection S o = 1 -3a primary imbibition S o = S or -3b shut-in4 water injection S o = S or -5 oil injection S o = 1 − Swi ∗ -hundred points on a logarithmic T 2 axis (see Chapter 2).6.2.4 Experimental procedureIn each experiment a dry core was saturated under vacuum with normal heavy wateror the buffered solutions, after which it was placed in the core holder. Subsequently,several fluid injection steps were performed during which the differential pressure wasmonitored and the (relative) permeabilities were determined. The steps are summarizedin Table 6.1. In the first four steps the amount of fluids injected varies between 10 and20 pore volumes (PV) per step. The flow rate was adjusted during each step such thatthe differential pressure did not exceed 1500 mbar. The absolute permeability, K abs , ofthe core was determined in step 1. Primary drainage of the core was done in step 2through the injection of pure oil. Stabilization of the differential pressure was alwaysobserved after injection of 10 to 20 PVs, indicating the core was at, or at least closeto irreducible water saturation conditions (S w = S wi ) and the relative permeability, k ro ,was determined. Similarly, water was injected in a secondary imbibition cycle (step 3)and the relative permeability, k rw , at residual oil saturation conditions (S w = 1 − S or )was determined. Secondary drainage was applied in step 4 in order to obtain a state ofirreducible water saturation again and to prepare the initial conditions before injecting theTMOS/oil mixture in step 5a. Between each step the amount of D 2 O in five different slicesand in absence of flow was determined through an NMR T 2 measurement as described inthe previous section. This was done to measure the saturation profiles.
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TWO-PHASE REACTIVE TRANSPORTOF AN O
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2 1. Introductionproducerbarrierlow
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Part ITwo-phase bulk systems7
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144 Appendix Awhere S 0 is a consta
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146 Appendix AThe 0.95 Tesla scanne
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148 Appendix B
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150 Appendix CwhereΩ A (θ) = −2
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152 Appendix C
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154 Appendix D
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156 Appendix Eand equal to zero in
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158 Appendix EAs the saturations, d
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160 Bibliography[12] B. Vinot, R. S
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162 Bibliography[40] M. D. Mantle a
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164 Bibliography[70] F. J. M. van d
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166 Bibliography[97] K. Yoshida, A.
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168 Bibliography[127] G. W. Scherer
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170 Bibliography
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172 Summaryand gelation rates. The
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174 Samenvattingwaterfase. De T 1 v
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176 List of publications
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178 Dankwoordimmer opgewekte stemmi
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