Optimum and robust 3D facies interpolation strategies in a heterogeneous coal zone (Tertiary As Pontes basin, NW Spain)

Abstract

Abstract:Coal exploration and mining in extensively drilled and sampled coal seams can benefit from 3D statistical facies interpolation. Starting from closely spaced core descriptions, and using interpolation methods, a 3D optimum and robust facies distribution model was obtained for a thick, heterogeneous coal seam zone deposited in the non-marine As Pontes basin (Oligocene-Early Miocene, NW Spain). Several grid layering styles, interpolation methods (truncated inverse squared distance weighting, truncated kriging, truncated kriging with an areal trend, indicator inverse squared distance weighting, indicator kriging, and indicator kriging with an areal trend) and searching conditions were experimented and the results compared. Facies interpolation strategies were evaluated using visual comparison and cross validation. Moreover, robustness of the resultant facies distribution with respect to variations in interpolation method input parameters was verified by taking into account several scenarios of uncertainty. The resultant 3D facies reconstruction improves the understanding of areal distribution and geometry of the coal facies. Furthermore, since some coal quality properties (e.g. calorific value or sulphur percentage) display a good statistical correspondence with facies, predicting the distribution of these properties using the Abstract:Coal exploration and mining in extensively drilled and sampled coal seams can benefit from 3D statistical facies interpolation. Starting from closely spaced core descriptions, and using interpolation methods, a 3D optimum and robust facies 2 correspondence with facies, predicting the distribution of these properties using the reconstructed facies distribution as a template proved to be a powerful approach, yielding more accurate and realistic reconstructions of these properties in the coal seam zone.

Geostatistical modeling of the gas emission zone and its in-place gas content for Pittsburgh-seam mines using sequential Gaussian simulation

“…Hindistan et al (2010) used kriging as a tool to predict and control coal quality during longwall mining so that produced coal would comply with certain product specifications. Falivene et al (2007) used geostatistical techniques to develop optimum and robust interpolation strategies in a heterogeneous coal zone in Spain. They concluded that optimum gridding, spatial correlation, and modeling can generate more accurate and realistic fades and coal property reconstructions.…”

Forecasting coal resources and reserves in heterogeneous coal zones using 3D facies models (As Pontes Basin, NW Spain)

“…These have been widely used to reconstruct or simulate facies distributions in the subsurface, mostly in relation to hydrocarbon reservoirs or aquifers (for example: Johnson and Dreisss, 1989;Langlais and Doyle, 1993;Gotway and Rutherford, 1994;de Marsily et al, 1998 andLee et al, 2007). However, examples of their application to coal zones are limited (Falivene et al, 2007b;Heriawan and Koike, 2008b;Deutsch and Wilde, 2013). …”

“…And the south-western passive margin recorded progressive onlap and expansion of the depositional areas of the basin, reaching 2.5km 2 during its late depositional stages (Figure 2B and C, Ferrús, 1998;Santanach et al, 2005). Coal deposition in 6AW took place in well-developed marshes and swamps; where tropical terrestrial and aquatic plant communities (Cavagnetto, 2002;Martin-Closas, 2003) were bordered by short radius alluvial fine-grained fans (Bacelar et al, 1988;Cabrera et al, 1995Cabrera et al, , 1996Ferrús, 1998;Sáez and Cabrera, 2002;Sáez et al, 2003;Falivene et al, 2007b). The deposits of the 6AW zone average 30m in thickness, and are affected by post-depositional tilting towards the northern and eastern basin margin and gentle folding (Santanach et al, 2005).…”

“…An hybrid approach is used: a) proportional layering between top and base in the centre of the basin and its northern and eastern active basin margins to reproduce post-depositional folded stratification and account for the near isochronous nature of the limits of the coal zone, and b) parallel to top layering for the southern passive margin to reproduce onlap of expansive intervals such as this one onto the basement (Cabrera et al, 1995;Ferrús, 1998;Santanach et al, 2005;Figure 5). This corresponds to the "geological layering" described in Falivene et al (2007b). Vertical grid spacing is set to approximately 0.15 m following the resolution of core descriptions.…”

“…Deterministic facies interpolations are obtained with indicator kriging (IK; Johnson and Dreiss, 1989;Deutsch and Journel, 1998;Falivene et al, 2007b; Figure 8A and 9A). IK yields a unique and smooth solution aiming at local accuracy (Isaaks and Srivastava, 1989;Journel et al, 2000) with the most probable facies category at each grid node (Yamamoto et al, 2012).…”