Changes

[[file:geological-heterogeneities_fig5.png|thumb|{{figure number|5}}Architectural elements of a barrier island sand body. (From <ref name=pt06r35>Galloway, W. E., Cheng, E. S. S., 1985, Reservoir facies architecture in a microtidal barrier system—Frio Formation, Texas Gulf Coast: The University of Texas Bureau of Economic Geology, Report of Investigations, v. 144, 36 p.</ref>.)]]

[[file:geological-heterogeneities_fig5.png|thumb|{{figure number|5}}Architectural elements of a barrier island sand body. (From <ref name=pt06r35>Galloway, W. E., Cheng, E. S. S., 1985, Reservoir facies architecture in a microtidal barrier system—Frio Formation, Texas Gulf Coast: The University of Texas Bureau of Economic Geology, Report of Investigations, v. 144, 36 p.</ref>.)]]

Elements of fieldwide variability include reservoir thickness, facies geometries and continuity, and bulk reservoir properties. Like interwell heterogeneity, heterogeneities at this scale are difficult to assess because information derived at smaller scales must be scaled up and generalized. Depositional models, determined by geological description at the smaller scales, provide the main basis for interpreting fieldwide reservoir architecture. (For more on depositional models, see [[Lithofacies and environmental analysis of clastic depositional systems]] and [[Carbonate reservoir models: facies, diagenesis, and flow characterization]].) It is very important to describe the reservoir at this scale adequately because reservoirs, being complex depositional systems, are often compartmentalized ([[:file:geological-heterogeneities_fig5.png|Figure 5]]), and separate compartments may not be in communication (see [[Evaluating stratigraphically complex fields]]).

Elements of fieldwide variability include reservoir thickness, facies geometries and continuity, and bulk reservoir properties. Like interwell heterogeneity, heterogeneities at this scale are difficult to assess because information derived at smaller scales must be scaled up and generalized. Depositional models, determined by geological description at the smaller scales, provide the main basis for interpreting fieldwide reservoir architecture. (For more on depositional models, see [[Lithofacies and environmental analysis of clastic depositional systems]] and [[Carbonate reservoir models: facies, diagenesis, and flow characterization#]].) It is very important to describe the reservoir at this scale adequately because reservoirs, being complex depositional systems, are often compartmentalized ([[:file:geological-heterogeneities_fig5.png|Figure 5]]), and separate compartments may not be in communication (see [[Evaluating stratigraphically complex fields]]).

Compartmentalization gives rise to regional patterns of variability in reservoir characteristics and production performance that directly reflect variability in facies distributions or, more precisely, geological flow units (see [[Flow units for reservoir characterization]]). Unfortunately, it is not always possible to uniquely define the depositional environment and facies distribution because the reservoir, and the geographic distribution of the database from which to formulate an interpretation, may be smaller than the entire depositional system from which the reservoir originates (see <ref name=pt06r139>Tillman, R. W., Jordan, D. W., 1987, Sedimentology and subsurface geology of deltaic forces, Admire GSO Sandstone, El Dorado field, Kansas, in Tillman, R. W., Weber, K. J., eds., Reservoir Sedimentology: SEPM Special Publication 40, p. 221–292.</ref> and <ref name=pt06r122>Slatt, R. M., Phillips, S., Boak, J. M., Lagoe, M. B., 1993, Scales of geological heterogeneity of a deep-water sand giant oil field, Long Beach unit, Wilmington field, California, in Rhodes, E. G., Moslow, T. F., eds., Marine Clastic Reservoirs—Examples and Analogs: New York, Springer-Verlag.</ref> for examples).

Compartmentalization gives rise to regional patterns of variability in reservoir characteristics and production performance that directly reflect variability in facies distributions or, more precisely, geological flow units (see [[Flow units for reservoir characterization]]). Unfortunately, it is not always possible to uniquely define the depositional environment and facies distribution because the reservoir, and the geographic distribution of the database from which to formulate an interpretation, may be smaller than the entire depositional system from which the reservoir originates (see <ref name=pt06r139>Tillman, R. W., Jordan, D. W., 1987, Sedimentology and subsurface geology of deltaic forces, Admire GSO Sandstone, El Dorado field, Kansas, in Tillman, R. W., Weber, K. J., eds., Reservoir Sedimentology: SEPM Special Publication 40, p. 221–292.</ref> and <ref name=pt06r122>Slatt, R. M., Phillips, S., Boak, J. M., Lagoe, M. B., 1993, Scales of geological heterogeneity of a deep-water sand giant oil field, Long Beach unit, Wilmington field, California, in Rhodes, E. G., Moslow, T. F., eds., Marine Clastic Reservoirs—Examples and Analogs: New York, Springer-Verlag.</ref> for examples).