Uncertainty analysis of fluvial outcrop data for stochastic reservoir modelling

Abstract

Uncertainty analysis and reduction is a crucial part of stochastic reservoir modelling and fluid flow simulation studies. Outcrop analogue studies are often employed to define reservoir model parameters but the analysis of uncertainties associated with sedimentological information is often neglected. In order to define uncertainty inherent in outcrop data more accurately, this paper presents geometrical and dimensional data from individual point bars and braid bars, from part of the low net:gross outcropping Tortóla fluvial system (Spain) that has been subjected to a quantitative and qualitative assessment. Four types of primary outcrop uncertainties are discussed: (1) the definition of the conceptual depositional model; (2) the number of observations on sandstone body dimensions; (3) the accuracy and representativeness of observed three-dimensional (3D) sandstone body size data; and (4) sandstone body orientation. Uncertainties related to the depositional model are the most difficult to quantify but can be appreciated qualitatively if processes of deposition related to scales of time and the general lack of information are considered. Application of the N 0 measure is suggested to assess quantitatively whether a statistically sufficient number of dimensional observations is obtained to reduce uncertainty to an acceptable level. The third type of uncertainty is evaluated in a qualitative sense and determined by accurate facies analysis. The orientation of sandstone bodies is shown to influence spatial connectivity. As a result, an insufficient number or quality of observations may have important consequences for estimated connected volumes. This study will give improved estimations for reservoir modelling.

Predicting the impact of sedimentological heterogeneity on gas–oil and water–oil displacements: fluvio-deltaic Pereriv Suite Reservoir, Azeri–Chirag–Gunashli Oilfield, South Caspian Basin

“…Channel orientation and the range of channel orientations may influence connectivity, particularly in low NTG reservoirs (Larue & Friedmann 2005;Martinius & Naess 2005;Larue & Hovadik 2006). Moreover, we hypothesize that on the north flank of the Azeri structure, injected gas may follow the channel orientation and thus flow obliquely down the flank rather than directly towards the nearest producer.…”

The application of outcrop analogues in geological modelling: a review, present status and future outlook

“…From an outcrop data acquisition point of view, uncertainty in the dataset is introduced if either: (i) the number of observations is insufficient and the natural variability is not appropriately captured; and/or (ii) the data accuracy and/or representativeness of a particular variable is insufficient (Martinius & Naess 2005). Therefore, natural variability within a depositional system has to be more prominently included in outcrop data acquisition and uncertainty analysis for reservoir modelling purposes.…”

Data capture for multiscale modelling of the Lourinhã Formation, Lusitanian Basin, Portugal: an outcrop analogue for the Statfjord Group, Norwegian North Sea

“…Statistical analysis of quantitative outcrop data enables us to better predict the distribution of fluvial sandstone bodies and their associated heterogeneities in the subsurface (Reynolds 1999;Martinius & Naess 2005;Fabuel-Perez et al 2010). Extraction of quantitative geometrical and geological data from outcrop allows us to create a database that can aid in the prediction of the 3D nature of fluvial sandstone bodies and their multiscale heterogeneities in the subsurface.…”

“…Understanding the distribution and geometries of these heterogeneities from subsurface data alone is often challenging. The use of outcrop analogues to supplement subsurface datasets has long been recognized as an important part of the exploration and early field development workflow (Bryant & Flint 1993;Dreyer et al 1993;Hodgetts et al 2004;Brandsaeter et al 2005;Martinius & Naess 2005;Enge et al 2007;Cabello et al 2011). As fields on the Norwegian Continental Shelf begin to enter their latelife phase, focus on increased oil recovery (IOR) related techniques becomes more important.…”