Using Log-Derived Bulk Volume Water and Nuclear Magnetic Resonance Logs to Indicate Producible Fluids

Mark H. Franklin and Terrilyn M. Olson

The bulk volume water fraction, as expressed by the product of log-derived water saturation and porosity, is useful in evaluating producible fluids. Experience shows that bulk volume water (BVW) is constant for a homogeneous formation above the transition zone, where hydrocarbon is produced water-free. Conversely, BVW is not constant in homogeneous formations within or below the transition zone, where water is producible. Consequently, a comparison of the irreducible bulk volume water (BVW_irr) of a formation and the log-measured BVW enables prediction of producible fluids.

This approach is illustrated using example logs from Hugoton Field, Kansas. The producing interval is the Chase Group, a complex mixture of clastics and carbonates. Lack of homogeneity requires modification of the traditional technique. In this case, regression analysis revealed a linear relationship between BVW_irr and spectral gamma ray measurements. This relationship was determined by comparison of spectral gamma ray measurements with log-derived BVW in gas-producing wells known to be above the transition zone. Nuclear magnetic resonance measurements provided an independent verification of irreducible bulk volume water.

When plotted in depth with porosity, the profile of BVW_irr and log-measured BVW indicates the presence of producible gas, producible water, and irreducible water, providing a powerful reservoir management tool.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California