Konstantina Katika

Nuclear magnetic resonance and sound velocity measurements of chalk saturated with magnesium rich brine

The use of low field Nuclear Magnetic Resonance (NMR) to determine petrophysical properties of reservoirs has proved to be a good technique. Together with sonic and electrical resistivity measurements, NMR can contribute to illustrate the changes on chalk elasticity due to different pore water composition. In this study we relate NMR data to changes in P-wave velocity and electrical resistivity. Core plugs from outcrop Stevns chalk, of 44% porosity, were divided into groups of three and saturated with deionized water, calcite equilibrated water, as well as sodium chloride and magnesium chloride solutions of the same ionic strength. Saturation with a solution that contained divalent ions caused a major shift on the distribution of the relaxation time. The changes were probably due to precipitats forming extra internal surface in the sample. Sonic velocities were relatively low in the MgCl2 solution saturated plugs.

Quantification of the Recovered Oil and Water Fractions during Water Flooding Laboratory Experiments

During core flooding experiments where water is injected in residual oil saturated core plugs, the fluids are often produced in small amounts. Oil and water come out of the core and are collected in glass vials using a fraction collector. Quantification of these fluids is often difficult since the volume might be less than a few microliters. In this study, we approach the determination of the oil volumes in flooding effluents using predetermined amounts of the North Sea oil with synthetic seawater. The UV/visible spectroscopy method and low-field NMR spectrometry are compared for this determination, and an account of advantages and disadvantages of each method is given. Both methods are reproducible with high accuracy. The NMR method was capable of direct quantification of both oil and water fractions, while the UV/visible spectroscopy quantifies only the oil fraction using a standard curve.

Nuclear Magnetic Resonance and Elastic Wave Velocity of Chalk Saturated with Brines Containing Divalent Ions

Nuclear magnetic resonance (NMR) has proven a good technique for measuring pore size distribution in reservoir rocks. The use of low field NMR together with sonic and electrical resistivity measurements, can contribute to illustrate the effect of adsorbing ions on chalk elasticity. NMR is useful for the study of the physical and chemical phenomena within saturated cores and sonic velocity is intimately connected to density and elastic constants of the rock. In this study we relate NMR data to changes in P-wave velocity due to ion adsorption. Core plugs from outcrop Stevns chalk, of ~45% porosity, were divided into groups of three and each group was saturated either with deionized water, calcite equilibrated water, or sodium chloride, magnesium chloride and calcium chloride solutions of the same ionic strength. Saturation with solutions that contain divalent ions caused major shifts in the distribution of the relaxation time. Core samples saturated with calcium chloride solution relaxed slower and those saturated with magnesium chloride solution relaxed faster than the rest of the samples. Along with the changes in relaxation the samples experienced smaller velocities of elastic waves when saturated with MgCl2 solution. Rock samples saturated with brines containing salts experienced lower electrical resistivity.

Wettability of quartz surface as observed by NMR transverse relaxation time (T2)

Injection of optimized water composition (smart water) is an advanced water flooding method for Enhanced Oil Recovery (EOR). Low saline waterflooding has proven successful in sandstone reservoirs. However, there is still controversy on the mechanism of smart water flooding. We studied the wettability property of the quartz surface by using Nuclear Magnetic Resonance (NMR) method. The principle of this method is that protons in water relax faster when it comes close to solid surface. We observed that quartz is highly water wet. A layer of water (bound water) forms on the quartz surface when they are mixed. The amount of bound water increases with the second power of specific surface area of particles. Addition of metal ions to the water in some cases increases the amount of bound water for same amount of surface area. We studied the affect of Ca2 , Mg2 and Na ions and observed that among these ions, the Mg2 ion produces the maximum amount of bound water while the Ca2 ion produces the least. The method demonstrated in this study could be used to decide the optimized water composition for waterflooding in sandstone reservoirs.