Reservoir Simulation and Reserves Classifications-Guidelines for Reviewing Model History Matches To Help Bridge the Gap Between Evaluators and Simulation Specialists
- Dean Channing Rietz (Ryder Scott Petroleum Consultants) | Adnan H. Usmani (Ryder Scott Company, L.P.)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 9-12 October, Dallas, Texas
- Publication Date
- Document Type
- Conference Paper
- 2005. Society of Petroleum Engineers
- 5.6.9 Production Forecasting, 5.4.1 Waterflooding, 4.3.4 Scale, 6.1.5 Human Resources, Competence and Training, 5.3.1 Flow in Porous Media, 5.5.7 Streamline Simulation, 4.2 Pipelines, Flowlines and Risers, 5.5 Reservoir Simulation, 5.6.4 Drillstem/Well Testing, 5.1.5 Geologic Modeling, 1.2.3 Rock properties, 5.8.8 Gas-condensate reservoirs, 4.6 Natural Gas, 5.5.3 Scaling Methods, 5.7.6 Reserves Classification, 3.3.6 Integrated Modeling, 5.5.8 History Matching, 5.2 Reservoir Fluid Dynamics
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As the scrutiny on oil and gas reserves continues to increase, the subject of evaluating reservoir simulation models has come to the forefront.Regulatory bodies, such as the U.S. Securities and Exchange Commission, do not provide detailed criteria on the use of reservoir simulation models in the reserves estimation process, other than their stated position that the model must have a "good history match".A great deal of high quality, highly technical research has been conducted in the field of history matching and of late in "automatic" history matching, and the paper reviews some of this research.While much of this research is useful, it is not clear that any particular quantitative assessment can be made of history match quality, or if such a method really helps to understand the applicability of the history matched model.It is easy to understand why reservoir simulation specialists and reserves estimators may be at odds as to the use and utility of a particular model.It is well recognized that, in general, only a limited amount of time is available to review models; thus, only a fraction of the time devoted to the original model construction can usually be devoted to the review process.
The authors have been on both sides of this dilemma, and this paper is intended to provide some suggestions for a systematic review of models (for whatever ultimate use) and start a dialogue to discuss how history matches should be evaluated with respect to reserves.It is noted that, for the most part, model reviews do not need to address whether a model is "perfect" overall, rather a review should address whether a model is fit for a particular purpose.The authors propose that the applicability of the model, and the quality of the history match can always be qualitatively assessed if one views the model as an analogy for a particular property.Therefore, the "analogy" approach suggested by the authors provides a specific methodology for incorporating simulation model results in the reserves estimation process.
Reservoir simulation continues to become more common as a tool to aid oil and gas professionals in the exploitation of hydrocarbon assets.Reservoir simulation quite simply is a mathematical (numerical rather than analytical) representation of a petroleum reservoir.Models are history matched so that under production constraints analogous to the production constraints imposed on the actual wells, the model behaves in a fashion similar to the actual wells.The assumption is that once the model reacts under the historical constraints as did the actual wells, then it will behave the same as the actual wells under future constraints.This is often incorrect, and one of the focuses of this paper is on validating this assumption.It seems obvious, but it is important to remember that the model is not the reservoir itself - it is really only a representation of, or an analogy to the reservoir.Thus the model can be used only as long as the analogy holds.
Once the model is built, history matched, and verified, it can be used for many purposes.Among these purposes is to test various alternative development scenarios for a field or reservoir, in order to attempt to optimize either recovery or economic returns."Attempt" is used here since in reality no one really ever knows what the optimum depletion scenario is.We can only compare, from a relative standpoint, how well a particular reservoir is performing.This is where the model can help - if we have a representative model of the reservoir and a desired development or economic objective, we can find the optimum development scenario for the model (from a specific series of cases) and from this we infer that the reservoir will be best developed using the same plan.
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