Probabilistic Approach to Reservoir Performance Predictions 

Top-down Modeling (TDM) versus Experimental Design or Design of Experiments (DoE) Method


The use of deterministic approach for the assessment of petroleum resources and reservoir performance predictions through different stages of oil & gas field life (acquisition, exploration, appraisal, development, production, and management) is generally in decline as the industry recognizes that the underlying subsurface uncertainties actually govern a range of outcomes and not just a few single-valued assessments.

While probabilistic approach has been widely employed by both majors and independents, especially during exploration and appraisal stages, the challenges that remain ongoing concerns include:

  • Identification of key uncertainties and types of distributions,
  • Determination of ranges and dependencies, and
  • The successful integration of subsurface geological uncertainties with operational and economic uncertainties.

None of these challenges are fully resolved, and these remain ongoing concerns, as these pose great risks in conceptual field development planning (FDP), selection, and thus capital investment.

The Experimental Design or Design of Experiments (DoE) method has proven to be the most popular technique to date, providing a systematic approach based on probabilistic principles resulting in a suitable range of outcomes to be considered by decision makers. The disadvantages of using the the DoE method as an uncertainty analysis tool include:

  • Its use of a proxy model as a substitute for full reservoir simulation,
  • The time and effort required for constructing a relatively large set of discrete reservoir models to set up proxy equations, and finally
  • Its selection of multiple reservoir models to be used for the forecast in the final stage at which point the method really tends to resemble a multi-scenario or multi-deterministic methodology.

Predicting reservoir performance is a critical task in all stages of an oil & gas field life. Due to the complex physics of the subsurface, the reservoir response is typically computed numerically using a numerical simulator. However, since the various input parameters used to build reservoir models contain inherent uncertainties, so do the output model forecasts. Therefore, correctly characterizing these uncertainties and probabilistically evaluating the model response are very important in assisting decision makers in making well-informed business decisions and achieving business goals.

The Top-down Modeling (TDM) tool provides a systematic approach in which reservoir performance is probabilistically evaluated without the use of a proxy model as is required in the Experimental Design or Design of Experiments (DoE) method. The TDM method delivers a fully probabilistic assessment of reservoir performance at considerable time and cost savings compared to the DoE method.

A&A Consulting Team of high-level and seasoned consultants has the expertise and extensive experience in utilizing the TDM tool, as well as the DoE method, resulting in considerable time and cost savings for our clients. 


We can put teams of our high-level and seasoned consultants, with extensive experience in conducting probabilistic reservoir performance predictions, utilizing the TDM tool, or the DoE method, to work on your company’s unconventional (shale) and conventional oil & gas fields, onshore or offshore, projects, whenever requested.

In addition, we will be delighted to conduct customized training workshops on probabalistic reservoir performance predictions, for the benefit of your company’s professionals and managers, at your company’s offices, around the world.

To put our high-level and seasoned consultants, subject matter experts (SME), to work on your company's probabilistic reservoir performance prediction projects, around the world, please contact us.  

Contact: +1-281-359-2674 or send us an e-mail

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