Reinvestment in, and the rejuvenation of, aging oil fields are becoming increasingly commonplace. Because the price of oil has stabilized at an equitable value and enhanced oil recovery methods have been proven, previously-depleted oil reservoirs are being revisited to determine their potential for tertiary recovery by means of CO 2 flooding. Accurate determinations of unswept oil and permeability distribution within the reservoir are critical elements in understanding and optimizing the CO 2 flood. This paper presents a pilot study in utilization of NMR logging in the redevelopment of a field that has been waterflooded since 1953.These mature reservoirs pose well-known challenges for formation evaluation. Resistivity-based saturation models are inadequate and uncertain because of previous waterfloods and variable formation water salinity (R w ) values. The variations in grain size and the onlapping of sand bodies cause uncertainty with the use of a porosity-permeability transform to estimate permeability.These challenges must be overcome for optimal well placement, infill drilling, CO 2 flood design, and other reservoir management practices. The standard logging suite for newly-drilled wells, triple combo and nuclear magnetic resonance (NMR), has evolved to address many of these challenges.This paper presents a pilot study that demonstrates the effectiveness of NMR logs for reservoir characterization. These reservoirs were evaluated for estimating formation porosity, bound and moveable fluid volumes, permeability, and remaining oil saturations. The log data were compared and calibrated with X-ray diffraction (XRD), Specialized Core Analysis (SCAL), and Capillary Pressure data from core. Pore-size distribution from NMR has been used to identify facies changes and for geomodeling purposes. Variations in the facies and the distribution of the sand bodies have been correlated to 3D seismic data. This has helped with the accurate mapping of the reservoir units to understand sweep efficiency. Production results are used to validate the log interpretations. A similar method can be used in other aging oil fields and to evaluate the development plan of a CO 2 flood.

A new wireline nuclear magnetic resonance (NMR) logging tool is capable of providing high-resolution logs at a logging speed that is twice that of the typical current MRIL® tool logging speeds. The new sensor features a stronger magnetic gradient to enhance the sensitivity of diffusion-based fluid typing; it also provides a much shorter inter-echo spacing (Te) to increase the data density per echo train. Consequently, the new sensor reduces the requirement of vertical averaging, which enhances the resolution of thin bed formation evaluation. The new NMR sensor addresses industry requirements for reliable porosity, organic vs. intergranular porosity discrimination, and free vs. adsorbed fluid fractions in low porosity, heterogeneous unconventional reservoir evaluations. The paper discusses optimization aspects of the sensor, including antenna aperture, maximized packing density of frequency bandwidth, and multi-frequency short inter-echo spacings. The new NMR sensor is fully combinable with several nuclear, electromagnetic (EM), and acoustic logging instruments with a log vertical resolution that is comparable to that of wireline density logs. Field tests from North American unconventional wells have demonstrated that only minimal stacking is needed to meet the 1 PU porosity repeatability and moderate stacking for reliable fluid typing, even in low porosity unconventional reservoirs. With an optimal number of frequencies used for unconventional reservoir applications, an advantage is realized from the total frequency bandwidth for optimal signal-to-noise ratio (SNR). The optimized SNR, in addition to the short Te, also improves the 1D T2 spectral and 2D map resolution and, consequently, free light hydrocarbon and organic pore fluids. Intergranular fluid signals are also resolved in several wells with porosity as low as ≤ 5 PU.