Towards a better understanding of nuclear magnetic resonance (NMR) measurements on well logs and rock cores - biannual report 2009

Object:

To extend and continue the finished project called 'Improved Characterization of Rock Cores Obtained by a Combined Use of Multivariate Analysis Techniques and Magnetic Resonance (NMR)’ and to explore new ideas connected to NMR. One major goal is to extract useful information from NMR logging data. The signal-to-noise ratio in such data is poor and makes data handling and algorithm design a challenge.

Another major goal is to extract information on rock permeability from NMR measurements. Permeability has so far been hard to predict. A possible strategy is to vary the inter-echo spacing. This may shed light on pore geometry. Another possible strategy is to combine different types of NMR experiments, such as T1/T2 measurements and PFG-NMR. If new algorithms and data handeling routines turn out to be successful, then user friendly implementations should result.

Status:

Fitting sums of exponentials and fitting sums of stretched exponentials are two common numerical problems encountered in the analysis of NMR measurements. In this last biannual period, the relationship between these two algorithms has been studiet extensively. There is a relationship between discrete stretched exponentials and distributed non-stretched exponentials that can be calculated and implemented in computer programs. However, to use this approach to fit sums of exponentials proved to be numerically unstable and too sensitive to noise.

Further research is being done on the relationship between the variation of inter-echo spacing and rock core permeability, a relationship which has been strongly indicated through chemometrics. Various approaches have been attempted in order to calculate this relationship in a direct manner. This study is important because rock core permeability is a vital parameter. At present, a good direct permeability estimation method is yet to be found.

Towards the project deadline, efforts will be undertaken to make the work done so far accessible to all the involved parties. The project is accomplished with the close collaboration with Dr. Geir Sørland, Anvendt Teknologi AS.