SCA2003-26: APPLICATION OF NMR DIFFUSION EDITING AS CHLORITE INDICATOR

• Main Authors: M D Hürlimann, A Matteson, J E Massey, D F Allen, E J Fordham, F Antonsen, H G Rueslåtten
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Carr; Norwegian Sea
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1060.2625; http://www.ux.uis.no/%7Es-skj/ipt/Proceedings/SCA.1987-2004/1-SCA2003-26.pdf

ABSTRACT We present a nuclear magnetic resonance (NMR) based study on a series of sandstone cores from a major reservoir in the Norwegian Sea. The cores have varying amounts of chlorite and were prepared in different saturation states. NMR measurements were performed using the standard Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence and the new diffusion editing method that is designed to separate diffusion and relaxation effects. This procedure generally results in more reliable S w values and we demonstrate here that it can also be used to derive an indicator of chlorite content. Since the measurement of diffusion editing can be performed with logging tools, this technique can be used directly in a reservoir for the improved determination of saturation and to estimate the chlorite content, with important implications for the assessment of reservoir quality. When the samples were saturated with a mixture of refined oil and brine it was generally difficult to separate the contributions of the two phases in the CPMG relaxation measurements. The relaxation time of the oil often overlapped significantly with the T 2 distribution of the brine signal. To overcome this problem, we used the technique of diffusing editing to obtain simultaneously diffusion and relaxation information and its correlation. This was achieved by preceding the standard short-echo-spacing CPMG sequence by an editing sequence that attenuates the amplitude of the signal according to diffusion in the applied gradient. In the current work, we implemented the diffusion editing by increasing the first two echo spacings systematically. Relaxation information is obtained from the signal decay after the diffusion encoding. This effectively orthogonalizes the diffusion and relaxation information and allows the extraction of diffusion -relaxation distribution functions. These two-dimensional D -T 2 maps can be used to extract information about important reservoir parameters such as water saturation, oil viscosity, wettability state and ...