Changes

[[File:M91FG192.JPG|thumb|300px|{{figure number|7}}Generalized map and cross sections showing major environments and facies associations of a barrier island-lagoonal system (from McCubbin<ref name=McCubbin />). Reprinted with permission from the AAPG.]]

[[File:M91FG192.JPG|thumb|300px|{{figure number|7}}Generalized map and cross sections showing major environments and facies associations of a barrier island-lagoonal system (from McCubbin<ref name=McCubbin />). Reprinted with permission from the AAPG.]]

Barrier islands form thick, well-sorted sand bodies with a tabular geometry ([[:File:M91FG192.JPG|Figure 7]]). They typically comprise a composite of beach, dune, and upper shoreface sandstones.<ref name=Galloway1986>Galloway, W. E., 1986, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0070/0007/0750/0787.htm Reservoir facies architecture of microtidal barrier systems]: AAPG Bulletin, v. 70, no. 7, p. 787–808.</ref> Barrier islands can be continuous for tens of kilometers along strike but may only be a few kilometers wide. Local heterogeneity can be provided by tidal channel inlet deposits. These form crosscutting lenticular pods, disrupting the layer-cake continuity of the barrier island body. Recent barrier island sediments on the South Carolina coast provide a modern analog and are described in detail by Sexton and Hayes (1996).

Barrier islands form thick, well-sorted sand bodies with a tabular geometry ([[:File:M91FG192.JPG|Figure 7]]). They typically comprise a composite of beach, dune, and upper shoreface sandstones.<ref name=Galloway1986>Galloway, W. E., 1986, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0070/0007/0750/0787.htm Reservoir facies architecture of microtidal barrier systems]: AAPG Bulletin, v. 70, no. 7, p. 787–808.</ref> Barrier islands can be continuous for tens of kilometers along strike but may only be a few kilometers wide. Local heterogeneity can be provided by tidal channel inlet deposits. These form crosscutting lenticular pods, disrupting the layer-cake continuity of the barrier island body. Recent barrier island sediments on the South Carolina coast provide a modern analog and are described in detail by Sexton and Hayes.<ref>Sexton, W. J., and M. O. Hayes, 1996, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0080/0006/0800/0831.htm Holocene deposits of reservoir-quality sand along the central South Carolina coastline]: AAPG Bulletin, v. 80, no. 6, p. 831–854.</ref>

Ambrose et al. (1997) gave an example from an oil field in Venezuela where sweep has resulted from preferential water encroachment along the sandstone-rich core of the barrier island depositional axis with bypassed oil remaining along the landward pinch-out edge.

Ambrose et al.<ref>Ambrose, W. A., F. P. Wang, M. S. Akhter, and J. Skolnakorn, 1997, Geologic controls on remaining oil in Miocene transgressive-barrier, coastal-plain, and mixed-load fluvial systems in the Miocene Norte area, Lake Maracaibo, Venezuela: Presented at the Society of Petroleum Engineers Annual Technical Conference and Exhibition, October 5–8, San Antonio, Texas, SPE Paper 38662, 10 p.</ref> gave an example from an oil field in Venezuela where sweep has resulted from preferential water encroachment along the sandstone-rich core of the barrier island depositional axis with bypassed oil remaining along the landward pinch-out edge.

Richardson et al. (1988b) noted that severe problems can arise where barrier islands show a jigsaw-puzzle arrangement with poorer quality and discontinuous macroforms. Displacing fluids are channeled through the barrier island sandstones and bypass the other units. Efforts should be made to target the poorer quality intervals for this reason. Ambrose et al. (1991) described a relatively low-permeability tidal inlet channel within the high-permeability barrier island facies association of the West Ranch reservoir of the Frio barrier-strand-plain play of Texas. Unswept oil is commonly found within the tidal inlet sand bodies or along the permeability contrast marking the boundary between the tidal inlet sediments and the enclosing barrier island sandstones.

Richardson et al.<ref>Richardson, J. G., J. B. Sangree, and R. M. Sneider, 1988, Coastal barrier reservoirs: Journal of Petroleum Technology, v. 40, no. 9, p. 1127–1128.</ref> noted that severe problems can arise where barrier islands show a jigsaw-puzzle arrangement with poorer quality and discontinuous macroforms. Displacing fluids are channeled through the barrier island sandstones and bypass the other units. Efforts should be made to target the poorer quality intervals for this reason. Ambrose et al.<ref>Ambrose, W. A., N. Tyler, and M. J. Parsley, 1991, Facies heterogeneity, pay continuity, and infill potential in barrier-island, fluvial, and submarine-fan reservoirs: Examples from the Texas Gulf Coast and Midland Basin, in A. D. Miall and N. Tyler, eds., The three-dimensional facies architecture of terrigenous clastic sediments and its implication for hydrocarbon discovery and recovery: SEPM Concepts in Sedimentology and Paleontology 3, p. 13–21.</ref> described a relatively low-permeability tidal inlet channel within the high-permeability barrier island facies association of the West Ranch reservoir of the Frio barrier-strand-plain play of Texas. Unswept oil is commonly found within the tidal inlet sand bodies or along the permeability contrast marking the boundary between the tidal inlet sediments and the enclosing barrier island sandstones.

==Back-barrier environments==

==Back-barrier environments==