Best Practice Reservoir Characterization for the Alberta Oilsands

Abstract Numerical modeling of Alberta's oil sands deposits is important for optimum resource management in mining and insitu extraction projects. The heterogeneous distribution of structural, lithological, and petrophysical properties coupled with limited samples leads to unavoidable geological and production uncertainty. Geostatistics is used to reduce these uncertainties fairly. Nevertheless, uncertainty always remains and operators are faced with making decisions in the presence of uncertainty. This presentation summarizes a workflow of current best practice geostatistical modeling techniques. A framework for making decisions in the face of uncertainty is also presented. Introduction Investment in the Alberta heavy oilsands is increasing while conventional oil production declines and offshore development remains costly. There are predictions that 75% of Canadian oil production will come from the Alberta oilsands by 2015. The Athabasca oilsands represent 144 billion barrels of crude reserves. Of this, however, only 15% is economically recoverable using surface mining extraction techniques. The remaining 85% is accessible by in-situ techniques such as steam-assisted-gravity-drainage (SAGD). Figure 1 illustrates the major considerations involved in a typical geostatistical workflow:geological background,data collection and cleaning,representative statistics,2D mapping,structural modeling,gridding,lithofacies modeling, andpetrophysical property modeling. A transfer function is used to convert geological uncertainty to production uncertainty. For mining, this function is often a calculation of recoverable reserves; for in-situ the function is often SAGD flow simulation. The main objective of using geostatistics is to provide realistic models of variability and a fair assessment ofuncertainty in production performance due to geological uncertainty. Best practice geostatistical techniques appropriate for the Alberta oilsands are assembled from the diverse library of available methods. However, even these recommended techniques cannot remove uncertainty. One is always faced with decision making in the face of uncertainty. Characterization of Alberta's oilsands is unquestionably important. The author's have undertaken a number of projects and have been assembling a handbook on how to model the McMurray formation. The first edition [1] published a number of years ago was quite popular. The second edition will be available by the end of 2006; contact the authors for more information. Geological Uncertainty Geological uncertainty is quantified with geostatistical techniques. The main steps and recommended techniques for a standard geostatistical workflow within a typical Alberta oilsands deposit are as follows. Geological Background The models of geological heterogeneity must be consistent with the most basic geological interpretations. A sequence stratigraphic approach can be considered [2]. A satisfactory understanding of the overall geological setting is necessary for subsequent geostatistical modeling steps such as making decisions of stationarity (how to pool data), modeling spatial correlation, and estimating petrophysical properties with trend models. Data Collection and Cleaning There are numerous types of geological data including hard core interpretations and soft well log profiles, seismic, and analogue outcrops. These are collected at the beginning of the study. The different data types represent different volume supports, have different quality, and may contain errors or be inconsistent in measuring the same geological p

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