THE PURPOSE OF THE PROJECT IS TO LINK PROTON MAGNETIC RELAXATION PARAMETERS TO POROUS MEDIUM FLOW PARAMETERS BY 2D AND 3D NMR OBSERVATION IN ORDER TO OBTAIN SATISFACTORY APPROXIMATE VALUES FOR LOCAL FLOW VELOCITIES IN POROUS MEDIUM PHASES.
Nuclear magnetic resonance (NMR) imaging and proton NMR imaging can improve the description of the properties of fluids in porous media because of the wide range of parameters which the can be used to measure simultaneously.
Images of fluids in porous media have already been produced, but their definition was not very good. It was considered to be valuable to determine firstly the most suitable pair (porous media, fluids) for magnetic resonance imaging (MRI). For this, a methodology was devised for the measurement of magnetic parameters which was applied to various pairs (porous media fluids). The relaxation times for 5 fluids saturating 3 porous media were measured using 4 magnetic fields. The results obtained show that the presence of the porous medium reduces the relaxation time of the fluids it contains.
MRI methods were modified for the display of fluids in porous media. A preliminary study was carried out using a medical imaging system. The use of an imaging system of this type is not satisfactory since, in the images obtained of fluids in porous media, the signal/noise ratio was not adequate.
This limitation is due to the fact that the gradient changing time within a Fourier transfer sequence is too high and does not enable signal acquisition early enough. To overcome this problem a filtered back projection method not requiring gradient changing within the pulse sequence was used. This method provides for the direct acquisition of a 3-dimensional volume (x, y, z). A device enabling quick changing of gradients without damaging spectroscopy systems was also needed. The device produced a 3-dimensional volume (x, y, delta) where delta is chemical shift which provides for fluid discrimination. The acquisition of the 3-dimensional (x, y, delta) produced an image for both fluids directly: 1 image in water and 1 in oil.
The images obtained were enhanced by 2-dimensional or 3-dimensional processing. The standard image reconstruction methods, based on acquisi tion by back projection, produce very noisy images. The use of a more suitable reconstruction method enhances them. The acquisition of the 3-dimensional volume (x, y, z) required the development of a 3-dimensional reconstruction method taken from tomography. Using this method, a true 3-dimensional image (x, y, z) can be obtained, for which the 3-dimensions are isotropic.
THE PROJECT CONSISTS IN DEFINING THE NMR DATA ACQUISITION AND PROCESSING METHODS. THE RESULTING INFORMATION SHOULD PROVIDE A GOOD SIGNAL/NOISE RATIO ON 1 MM THICK CORE SLICES, WITH A SPATIAL RESOLUTION OF ABOUT 1 MM.
THE WORK PROGRAMME INCLUDES SIX STAGES:
- THEORETICAL STUDY OF THE PROTON NMR CONTRIBUTION TO THE STUDY OF POROUS MEDIA AND POROUS MEDIUM FLOWS,
- DEVELOPMENT OF METHODS FOR MEASURING THE T1 AND T2 RELAXATION TIMES,
- STUDY OF THE EFFECT OF THE TYPE OF HYDROCARBON, THE POROUS MEDIUM AND THE MAGNETIC FIELD ON THESE PARAMETERS,
- IMPROVEMENT OF THE METHODS FOR DEFINING OBSERVATION ZONES,
- IMPROVEMENT OF ACQUISITION METHODS,
- DEVELOPMENT OF PROCESSING SOFTWARES FOR 2D AND 3D DATA.
THESE WORKS SHOULD MAKE IT POSSIBLE TO MONITOR, IN A FUTURE PROJECT, SATURATION DEVELOPMENT IN A SMALL CORE FORM A POROUS MEDIUM, WITH GOOD SPATIAL RESOLUTION AND A GOOD SIGNAL/NOISE RATIO.