Changes

[[file:M91FG179.JPG|thumb|300px|{{figure number|8}}Net sand isochore map of the Q reservoir in the Little Creek field in Mississippi. The reservoir comprises three connected point bar sandstones in a background of floodplain mudstones and siltstones. Just to the north is the Sweetwater field, which produces from a depositionally isolated point bar in the same meander belt system (from Werren et al., 1990). Reprinted with permission from, and © by, Springer Ltd.]]

[[file:M91FG179.JPG|thumb|300px|{{figure number|8}}Net sand isochore map of the Q reservoir in the Little Creek field in Mississippi. The reservoir comprises three connected point bar sandstones in a background of floodplain mudstones and siltstones. Just to the north is the Sweetwater field, which produces from a depositionally isolated point bar in the same meander belt system (from Werren et al., 1990). Reprinted with permission from, and © by, Springer Ltd.]]

Technical papers indicate that connectivity in meander belt sediments can be highly variable and prone to chance factors. An example of this is the Little Creek field in Mississippi.<ref name=Werrenetal_1990 /> The lower reservoir unit comprises three connected point bar sandstones ([[:file:M91FG179.JPG|Figure 8]]). The Sweetwater field immediately to the north is believed to form part of the same fluvial system and produces from a fourth point bar sand body along the same trend. Nevertheless, the Sweetwater field is isolated from the Little Creek field on the evidence of a 24-m (79-ft) higher oil-water contact. The two fields are thought to be separated by a shale plug or an area with relatively high capillary displacement pressure. A similar observation was made by Carter<ref name=Carter_2003 /> for a meander belt reservoir in the Widuri field in the Java Sea. Following the depletion of a well on the updip side of a 100-m (328-ft)-wide abandoned channel, a second well was drilled on the opposite site of the clay plug. A full oil column was found in the new well, unaffected by production from the previous well. In the Saddle Lake area of Alberta, Canada, oil and gas pools are restricted to point bars completely surrounded by clay plugs.<ref name=Edieandandrichuk_2003>Edie, R. W., and J. M. Andrichuk, 2003, [http://bcpg.geoscienceworld.org/content/51/3/253.short Meander belt entrapment of hydrocarbons at Saddle Lake, Alberta and an untested in situ combustion scheme for recovery of heavy oil]: Bulletin of Canadian Petroleum Geology, v. 51, no. 3, p. 253–274.</ref>

Technical papers indicate that connectivity in meander belt sediments can be highly variable and prone to chance factors. An example of this is the Little Creek field in Mississippi.<ref name=Werrenetal_1990 /> The lower reservoir unit comprises three connected point bar sandstones ([[:file:M91FG179.JPG|Figure 8]]). The Sweetwater field immediately to the north is believed to form part of the same fluvial system and produces from a fourth point bar sand body along the same trend. Nevertheless, the Sweetwater field is isolated from the Little Creek field on the evidence of a 24-m (79-ft) higher oil-water contact. The two fields are thought to be separated by a shale plug or an area with relatively high capillary [[displacement pressure]]. A similar observation was made by Carter<ref name=Carter_2003 /> for a meander belt reservoir in the Widuri field in the Java Sea. Following the depletion of a well on the updip side of a 100-m (328-ft)-wide abandoned channel, a second well was drilled on the opposite site of the clay plug. A full oil column was found in the new well, unaffected by production from the previous well. In the Saddle Lake area of Alberta, Canada, oil and gas pools are restricted to point bars completely surrounded by clay plugs.<ref name=Edieandandrichuk_2003>Edie, R. W., and J. M. Andrichuk, 2003, [http://bcpg.geoscienceworld.org/content/51/3/253.short Meander belt entrapment of hydrocarbons at Saddle Lake, Alberta and an untested in situ combustion scheme for recovery of heavy oil]: Bulletin of Canadian Petroleum Geology, v. 51, no. 3, p. 253–274.</ref>

It seems from these case examples that clay plugs can be an important element limiting horizontal connectivity in meander belt sediments ([[:file:M91FG176.JPG|Figure 5d]]). Some point bars show flow connectivity with each other, others do not. Connectivity may be effective where the clay plug does not totally separate two point bars areally. Richardson et al.<ref name=Richardsonetal_1987>Richardson, J. G., J. B. Sangree, and R. M. Sneider, 1987, Meandering stream reservoirs: Journal of Petroleum Technology, v. 39, no. 12, p. 1501–1502.</ref> noted that there is commonly some sand or gravel underneath clay plugs that can allow communication. Similar observations have been made by Donselaar and Overeem.<ref name=Donselaarandovereem_2008>Donselaar, M. E., and I. Overeem, 2008, [http://archives.datapages.com/data/bulletns/2008/09sep/BLTN07079/BLTN07079.HTM Connectivity of fluvial point bar deposits: An example from the Miocene Huesca fluvial fan, Ebro basin, Spain]: AAPG Bulletin, v. 92, no. 9, p. 1109–1129.</ref> Clay plugs occur at the same level of the point bar that it partially encloses. If vertical connectivity is effective between incised point bars, the clay plug obstruction can be bypassed above and below. If no effective vertical communication occurs, then clay plugs are more likely to act as lateral flow barriers ([[:file:M91FG176.JPG|Figure 5e]]).

It seems from these case examples that clay plugs can be an important element limiting horizontal connectivity in meander belt sediments ([[:file:M91FG176.JPG|Figure 5d]]). Some point bars show flow connectivity with each other, others do not. Connectivity may be effective where the clay plug does not totally separate two point bars areally. Richardson et al.<ref name=Richardsonetal_1987>Richardson, J. G., J. B. Sangree, and R. M. Sneider, 1987, Meandering stream reservoirs: Journal of Petroleum Technology, v. 39, no. 12, p. 1501–1502.</ref> noted that there is commonly some sand or gravel underneath clay plugs that can allow communication. Similar observations have been made by Donselaar and Overeem.<ref name=Donselaarandovereem_2008>Donselaar, M. E., and I. Overeem, 2008, [http://archives.datapages.com/data/bulletns/2008/09sep/BLTN07079/BLTN07079.HTM Connectivity of fluvial point bar deposits: An example from the Miocene Huesca fluvial fan, Ebro basin, Spain]: AAPG Bulletin, v. 92, no. 9, p. 1109–1129.</ref> Clay plugs occur at the same level of the point bar that it partially encloses. If vertical connectivity is effective between incised point bars, the clay plug obstruction can be bypassed above and below. If no effective vertical communication occurs, then clay plugs are more likely to act as lateral flow barriers ([[:file:M91FG176.JPG|Figure 5e]]).