An integrated reservoir study represents the one reservoir modeling technique available to a reservoir management team that incorporates ALL of the information available regarding a petroleum reservoir. As such, the integrated study has the potential to provide the team with the highest resolution most accurate description of their field that is currently available. However, that high resolution comes at the expense of a highly complex, data intensive process. This paper was an attempt to simplify and codify the complex process of performing an integrated reservoir study.

The paper presents an overview of the integrated reservoir modeling process including how that process has changed from the early days of reservoir simulation to the present day. Two models are presented that illustrate the study process for a 1980 time frame multi reservoir study and a 2002 time frame geostatistically based compositional reservoir model.

Emphasis is placed on the changes in workflows from the early models — simple mapping of properties and manual digitization of maps to simulation model grids — to the more complex models of today — with property distributions based on object modeling and geostatistical analysis to distribute reservoir properties.

Through the examples, the paper illustrates the point that reservoir studies have evolved from a time when the geologists and engineers often knew more about their reservoirs than the available modeling tools would allow them to implement in their models - dual porosity and flow across faults, for example - to the point where today we often have the modeling capability to model more complex phenomena than our knowledge of the reservoir may warrant - for example, object modeling with no data on the characteristics of lithofacies in our reservoir, or dual porosity flow models with no data on fracture spacing and distribution.

The Integrated Study Conceptually

Although the term "Integrated Study" only gained widespread use in the 1990's 2,3,4, the conceptual tasks needed to build a model of a reservoir have been identified and performed since the advent of multi-well full field simulation studies. Those tasks — structural interpretation, petrophysical analysis, stratigraphic analysis, fluid PVT analysis, and reservoir simulation - have formed the basis for building models since the 1970's and continue today to be the backbone of the "Integrated Study" concept.

What has changed in the Integrated Study concept is:

  • The switch from the analog to digital form for the data input and analysis results of the "geo-science" tasks of the studies

  • The development of ever more mechanistically sophisticated analysis tools, for example

    • Object modeling in facies identification work

    • Geostatistical methods in distributing petrophysical properties inter-well,

    • Arbitrary connections in simulators to allow modeling of faults and fractures

  • Many orders of magnitude faster computers and greater data storage capacity

As a result of the sophisticated tools and greater computing capacity, the focal point of all of the model building process has moved from the reservoir simulation "dynamic" model in the integrated study concept of the 1980's, Figure 1, to the geologic "static" model today. This movement of the focal point is, we believe, a major reason for the greater interaction between the disciplines and tasks that is the emphasis of the 2003 integrated study concept, Figure 2.

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