Abstract
Proper reservoir evaluation in carbonate and sandstone environments has always been a challenge. Petrophysicists are constantly struggling with water salinity uncertainty and Archie's exponents (m and n). These parameters are often not readily available, require time-consuming special core analysis and can vary significantly within and across depositional sequences. A new generation of dielectric technology, which provides reliable measurements that overcomes some of the limitations of the old devices, is used. The enhanced data from the tool improves petrophysical formation evaluation in a variety of borehole environments.
Measurements from dielectric devices have been available via wireline conveyance for more than three decades. Several devices operating with a single-frequency were built in the eighties. Most failed to gain acceptance due to measurement limitations affected by borehole and invasion effects, and moderate accuracy making their interpretation complicated. Based on recent technology developments, a new device measuring both permittivity and conductivity at multiple frequencies has enabled petrophysicists to evaluate the petrophysical properties in various complex environments.
The combination of dielectric with other conventional logging measurements had been utilized in many wells to determine water saturation and remaining hydrocarbon saturation on a regular basis. In addition, the continuous variable Archie's exponent "MN" measurement from dielectric is used to estimate accurately water saturation. The difference in volume of total porosity and the dielectric quantification of water filled porosity (WFP) is used to estimate hydrocarbon saturation. A new approach for identifying and quantifying gas thinly bedded sands is tested with promising results. It combines high resolution dielectric measurements, borehole images and nuclear magnetic resonance (NMR) measurements. Integration of dielectric data to the conventional open-hole logging suites enables rapid and accurate results during the logging operation and allows proper decisions on pressure points to optimize logging time and reduce substantial cost.
Saudi Aramco has been leading the tests of the technology in a diverse range of environments and for various applications. The development and theory behind the dielectric measurements are discussed. Examples highlighting the value of these new measurements for improved formation evaluation in both carbonate and sandstone environments are provided in the paper.
