Reservoir Characterization Flashcards

What is the significance of the 'Dykstra-Parsons coefficient' (VDP) in reservoir characterization?

Answer: It quantifies vertical permeability heterogeneity; values near 1.0 indicate highly heterogeneous reservoirs

VDP ranges from 0 (homogeneous) to 1 (infinitely heterogeneous) and is derived from the log-normal permeability distribution of core plug data.

In 4D (time-lapse) seismic monitoring, what changes are primarily being tracked over time?

Answer: Changes in fluid saturation and pressure within the reservoir during production

4D seismic detects acoustic impedance changes caused by fluid substitution (e.g., oil replaced by water or gas) and pressure depletion as the reservoir is produced.

Which rock physics model relates changes in pore fluid to seismic velocity, forming the basis for fluid substitution in seismic interpretation?

Answer: Gassmann's equation

Gassmann's equations predict how P-wave velocity changes when one fluid replaces another in the pore space, assuming low-frequency and uniform pore pressure equilibration.

What is the primary limitation of using arithmetic average permeability to characterize a layered reservoir system for flow simulation?

Answer: It over-weights high-permeability layers and overestimates flow capacity in series-flow (vertical) configurations

For series (vertical) flow across layers, the harmonic average is appropriate; arithmetic averaging biases toward high-k layers and overestimates effective permeability.

In natural fracture characterization, which borehole image log is most commonly used to identify fracture orientation and aperture?

Answer: Formation Micro-Imager (FMI) or Fullbore Formation MicroImager

FMI logs use micro-resistivity pads pressed against the borehole wall to create high-resolution 360° images, revealing fracture traces, orientation, and aperture.

What does 'upscaling' refer to in the context of building a reservoir simulation model from a geological model?

Answer: Converting fine-scale geological grid properties to coarser simulation grid cells while preserving flow behavior

Upscaling averages or flow-simulates fine-scale geological properties (porosity, permeability) onto coarser simulation grids to make dynamic simulation computationally feasible.

Which factor most controls the transition zone thickness between free water level and the hydrocarbon-water contact in a reservoir?

Answer: Capillary pressure characteristics governed by pore throat size distribution

The transition zone height is controlled by capillary pressure curves; fine-grained rocks with small pore throats have thick transition zones, while coarse rocks have sharp contacts.