Michael L. Batzle¹, De-hua Han²
(1) Colorado School of Mines, Golden, CO
(2) Houston Advanced Research Center, The Woodlands

Abstract: Realistic pore fluid properties

Fluid identification and monitoring are the ultimate goals of almost all of our seismic data acquisition and analysis efforts. Seismic attributes such as amplitude versus offset (AVO) are directly dependent on the influence of the pore fluids. To be effective, we must understand the specific properties of our target fluids and how these relate to physical processes involved within reservoirs and with different engineering techniques. During the life of a reservoir, fluids are extracted or replaced. Pressure, temperature, or density changes also occur and can and will compete with the effects due to fluid replacement. Small concentrations of free gas can appear even during liquid or supercritical injection.

The important seismic properties of in situ fluids are systematically dependent on composition. For oils, this involves the oil gravity or density and the gas content (GOR). Lighter components in oils will reduce the modulus and density substantially. Properties vary continuously over the range of compositions, and the distinction between 'gas' or 'liquid' is often not realistic. Phase boundaries also are often encountered under in situ conditions. These boundaries may be critical to the seismic response, as when light gases evolve at low pressure. In contrast, other boundaries are seismically invisible, as when liquids condense below the dew point. Fortunately, many of these fluid effects are predictable and our seismic attribute can be tuned to prevent misinterpretation.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana