Changes

Nevertheless, it probably does not take much for the connectivity between the various sand bodies in a meander belt to be disrupted. The connections between the various macroforms are likely to be through apertures of limited cross-sectional area such as erosional windows, crossovers, and crevasse splay-point bar intersections. Carbonate cementation of the basal lag by circulating groundwater can create permeability barriers at the base of individual point bars. Precipitation of carbonate cement may be accentuated where calcrete fragments form part of the basal lag.<ref name=Mckieandaudretsch_2005>Mckie, T., and P. Audretsch, 2005, Depositional and structural controls on Triassic reservoir performance in the Heron cluster, ETAP, central North Sea, in A. G. Dore and B. A. Vining, eds., Petroleum geology: Northwest Europe and global perspectives: Proceedings of the 6th Petroleum Geology Conference, Geological Society (London), p. 285–297.</ref>

Nevertheless, it probably does not take much for the connectivity between the various sand bodies in a meander belt to be disrupted. The connections between the various macroforms are likely to be through apertures of limited cross-sectional area such as erosional windows, crossovers, and crevasse splay-point bar intersections. Carbonate cementation of the basal lag by circulating groundwater can create permeability barriers at the base of individual point bars. Precipitation of carbonate cement may be accentuated where calcrete fragments form part of the basal lag.<ref name=Mckieandaudretsch_2005>Mckie, T., and P. Audretsch, 2005, Depositional and structural controls on Triassic reservoir performance in the Heron cluster, ETAP, central North Sea, in A. G. Dore and B. A. Vining, eds., Petroleum geology: Northwest Europe and global perspectives: Proceedings of the 6th Petroleum Geology Conference, Geological Society (London), p. 285–297.</ref>

Abundant mud chips caked along the base of point bars have the potential to attenuate communication. For example, Chapin and Mayer<ref name=Chapinandmayer_1991 /> found that the vertical connectivity between stacked point bars was severely impeded by mudstone-rich lags at the base of individual point bars in the reservoir of the Peoria field in Colorado. Doyle and Sweet<ref name=Doyleandsweet_1995> Doyle, J. D., and M. L. Sweet, 1995, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0079/0001/0050/0070.htm Three-dimensional distribution of lithofacies, bounding surfaces, porosity, and permeability in a fluvial sandstone—Gypsy Sandstone of northern Oklahoma]: AAPG Bulletin, v. 79, no. 1, p. 70–95.</ref> found that mudclast lags at the base of point bar sandstones have a patchy distribution in the Gypsy Sandstone of Northern Oklahoma. They consider them more likely to form baffles to flow instead of continuous barriers. Shanley<ref name=Shanley_2004 /> noted that where basal lags contain abundant mudclasts, they can be mistaken for shales on the gamma-ray log. Caution should be taken where a shale-like wireline log response is seen within thick multistory fluvial sandstones.

Abundant mud chips caked along the base of point bars have the potential to attenuate communication. For example, Chapin and Mayer<ref name=Chapinandmayer_1991 /> found that the vertical connectivity between stacked point bars was severely impeded by [[mudstone]]-rich lags at the base of individual point bars in the reservoir of the Peoria field in Colorado. Doyle and Sweet<ref name=Doyleandsweet_1995> Doyle, J. D., and M. L. Sweet, 1995, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0079/0001/0050/0070.htm Three-dimensional distribution of lithofacies, bounding surfaces, porosity, and permeability in a fluvial sandstone—Gypsy Sandstone of northern Oklahoma]: AAPG Bulletin, v. 79, no. 1, p. 70–95.</ref> found that mudclast lags at the base of point bar sandstones have a patchy distribution in the Gypsy Sandstone of Northern Oklahoma. They consider them more likely to form baffles to flow instead of continuous barriers. Shanley<ref name=Shanley_2004 /> noted that where basal lags contain abundant mudclasts, they can be mistaken for shales on the gamma-ray log. Caution should be taken where a shale-like wireline log response is seen within thick multistory fluvial sandstones.

[[Coal]]s commonly act as significant flow barriers where they occur in more humid fluvial systems. The precursor [[peat]] deposits to coal occur as thick mats of flexible and intertwined plant material and these can withstand strong erosive forces to stay substantially intact.

[[Coal]]s commonly act as significant flow barriers where they occur in more humid fluvial systems. The precursor [[peat]] deposits to coal occur as thick mats of flexible and intertwined plant material and these can withstand strong erosive forces to stay substantially intact.