Changes

Elements of interwell scale heterogeneity include lateral bedding geometries, styles, and continuity; systematic lateral and vertical textural patterns; and resultant variations in [[reservoir quality]]. This scale of heterogeneity is probably the most difficult to quantify because wellbore data of the type previously described must be extrapolated to the interwell region. In many instances, between well correlations are difficult because lithofacies may not be continuous at interwell spacings. Thus, interpretation must be guided by an understanding of depositional environments and facies, interpreted from core analysis and compared with modern environments or outcrop analogs where actual observations and measurements have been made.

Elements of interwell scale heterogeneity include lateral bedding geometries, styles, and continuity; systematic lateral and vertical textural patterns; and resultant variations in [[reservoir quality]]. This scale of heterogeneity is probably the most difficult to quantify because wellbore data of the type previously described must be extrapolated to the interwell region. In many instances, between well correlations are difficult because lithofacies may not be continuous at interwell spacings. Thus, interpretation must be guided by an understanding of depositional environments and facies, interpreted from core analysis and compared with modern environments or outcrop analogs where actual observations and measurements have been made.

Relatively few reliable quantitative studies of depositional environments and facies have been published, and those that have suggest considerable variability in interwell scale heterogeneities among different depositional systems, as well as within any one system. Excellent examples include Scheihing and Gaynor<ref name=pt06r38>Gaynor, G. C., Scheihing, M. H., 1988, Shelf depositional environments and reservoir characteristics of the Kuparuk River Formation (Lower Cretaceous), Kuparuk field, North Slope, Alaska, in Lomando, A. J., Harris, P. M., eds., Giant oil and gas fields—A core workshop: Society of Economic Paleontologists and Mineralogists Core Workshop 12, p. 333–389.</ref> and Krause et al.<ref name=pt06r67>Krause, F. F., Collins, H. N., Nelson, D. A., Mochemer, S. D., French, P. R., 1987, Multiscale anatomy of a reservoir— geological characterization of Pembina-Cardium pool, west-central Alberta, Canada: AAPG Bulletin, v. 71, p. 1233–2260.</ref> for shelf sandstones; van de Graaff and Ealey<ref name=pt06r144 /> for fluviodeltaic sequences ([[:file:geological-heterogeneities_fig3.png|Figure 3]]); and Jordan and Pryor<ref name=pt06r61>Jordan, D. W., Pryor, W. A., 1992, Hierarchical levels of heterogeneity in a Mississippi River meander belt and application to reservoir systems: AAPG Bulletin, v. 76, p. 1601–1624.</ref> for fluvial sands.

Relatively few reliable quantitative studies of depositional environments and facies have been published, and those that have suggest considerable variability in interwell scale heterogeneities among different depositional systems, as well as within any one system. Excellent examples include Scheihing and Gaynor<ref name=pt06r38>Gaynor, G. C., Scheihing, M. H., 1988, Shelf depositional environments and reservoir characteristics of the Kuparuk River Formation (Lower Cretaceous), Kuparuk field, North Slope, Alaska, in Lomando, A. J., Harris, P. M., eds., Giant oil and gas fields—A core workshop: Society of Economic Paleontologists and Mineralogists Core Workshop 12, p. 333–389.</ref> and Krause et al.<ref name=pt06r67>Krause, F. F., Collins, H. N., Nelson, D. A., Mochemer, S. D., French, P. R., 1987, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0071/0010/1200/1233.htm Multiscale anatomy of a reservoir— geological characterization of Pembina-Cardium pool, west-central Alberta, Canada]: AAPG Bulletin, v. 71, p. 1233–2260.</ref> for shelf sandstones; van de Graaff and Ealey<ref name=pt06r144 /> for fluviodeltaic sequences ([[:file:geological-heterogeneities_fig3.png|Figure 3]]); and Jordan and Pryor<ref name=pt06r61>Jordan, D. W., Pryor, W. A., 1992, Hierarchical levels of heterogeneity in a Mississippi River meander belt and application to reservoir systems: AAPG Bulletin, v. 76, p. 1601–1624.</ref> for fluvial sands.

[[file:geological-heterogeneities_fig4.png|thumb|{{figure number|4}}Synthetic reservoir cross section showing the vertical and lateral distribution of shales (black) within a sandstone (white) sequence. (Modified from <ref name=pt06r44 />.)]]

[[file:geological-heterogeneities_fig4.png|thumb|{{figure number|4}}Synthetic reservoir cross section showing the vertical and lateral distribution of shales (black) within a sandstone (white) sequence. (Modified from <ref name=pt06r44 />.)]]