Action Learning Module Information       Close
Flow Unit Determination

Competency Statement:

Establish flow units within the reservoir.

Learning Objective:

Upon completing this Learning Module assignment, the participant should be able to
  • Establish the areal and vertical distribution of zones with similar behavior in agreement with the reservoir model.
  • Identify and delineate the rock volumes with sedimentological, petrophysical and reservoir properties that enable hydraulic communication.

Assignment Instruction:

Most reservoirs are not homogeneous. Rather, they exhibit complex variations in continuity, thickness patterns and other properties, including porosity, permeability and capillary pressure. A reservoir is typically subdivided into zones or areas based upon differences in rock properties. The complexity of reservoir rock imposes a challenge to geoscientists and engineers in applying available technologies and their experience to improving oil and gas recovery.

The purpose of geological mapping is to identify flow units that contain oil and gas, and once they are found, to apply geologic evidence and concepts toward achieving the most efficient development and production of these prospects. However, it is important to remember that these geologic maps are never finished. When new wells are drilled or old wells are re-examined, new information becomes available, and the extent and geometry of flow units must be updated. Original maps may be based upon a few scattered control points. This means that in the early stages of geological work, a careful study of the local area should be made.

Lithofacies maps are quite helpful in defining various reservoir rock types. The correlation of a number of reservoir properties, including porosity and permeability, becomes much more meaningful when applied to a specific rock type.

During the production phase of a reservoir, more information about flow units is obtained by transient well testing and careful monitoring of individual well performance. Reservoir pressure maps are particularly useful for evaluating reservoir continuity. The areal distribution of reservoir pressure in different zones as a function of time can help us to identify pay discontinuities and flow barriers. Vertical pressure profiles are also useful in defining the effect of vertical permeability within a given reservoir section.

History matching of field performance, using a numerical reservoir simulator, can provide great insight into the continuity of flow units and reservoir properties in inter-well areas where there is no measurements. In this process, the geological properties such porosity, permeability and pay continuity are changed in order to match the observed field performance.

Different steps in gathering data for flow unit determination are:

In the geological phase:

  • General reservoir configuration
  • Fluids distribution
  • Continuity and thickness
  • Rock type, porosity and permeability cutoffs
  • Fluid contacts
  • Vertical stratification

During the production phase:

  • Logging
  • Well performance
  • Well testing
  • Relative permeability, capillary pressure and wettability tests
  • Inter-well tracers

In this assignment, you will be taking a short break from your work in the Sucre field, while the geologists on the reservoir management team prepare an analysis of some of the information that has been gathered so far from the upper/middle sands. During this time you will work on identifying the flow units within another reservoir where your company is actively involved in the Nuri formation.