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Line 15: − Youlumne is a giant oil field in the San Joaquin Basin, California ([[:file:Mth14ch02f01.jpg|Figure 1]]), that has produced, through December 2000, more than 17.2 million m<sup>3</sup> (108 million bbl) of oil and 2.7 billion m<sup>3</sup> (94 billion ft<sup>3</sup>) of gas from upper Miocene, deep-water sandstones known as the Stevens ([[:file:Mth14ch02f01.jpg|Figure 1]]). + Line 22:
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Yowlumne is a giant oil field in the San Joaquin Basin, California ([[:file:Mth14ch02f01.jpg|Figure 1]]), that has produced, through December 2000, more than 17.2 million m<sup>3</sup> (108 million bbl) of oil and 2.7 billion m<sup>3</sup> (94 billion ft<sup>3</sup>) of gas from upper Miocene, deep-water sandstones known as the Stevens ([[:file:Mth14ch02f01.jpg|Figure 1]]).
These sandstones, which represent classic facies of organic-rich shales in the Monterey Formation ([[:file:Mthch02f02.jpg|Figure 2]]), are some of the most prolific reservoirs in the basin and have contributed about 15% of more than 1.9 billion m<sup>3</sup> (12.3 billion bbl) of oil produced in the area since 1864. Because Stevens oils derive from Monterey Shale source rocks, Yowlumne is part of a Monterey-Stevens petroleum system (Graham and Williams).<ref name=Grahamandwilliams_1985>Graham, S. A., and L. A. Williams, 1985, [http://archives.datapages.com/data/bulletns/1984-85/data/pg/0069/0003/0350/0385.htm Tectonic, depositional, and diagenetic history of Monterey Formation (Miocene), central San Juaquin Basin, California]: AAPG Bulletin, v. 69, p. 385-411.</ref>
These sandstones, which represent classic facies of organic-rich shales in the Monterey Formation ([[:file:Mthch02f02.jpg|Figure 2]]), are some of the most prolific reservoirs in the basin and have contributed about 15% of more than 1.9 billion m<sup>3</sup> (12.3 billion bbl) of oil produced in the area since 1864. Because Stevens oils derive from Monterey Shale source rocks, Yowlumne is part of a Monterey-Stevens petroleum system (Graham and Williams).<ref name=Grahamandwilliams_1985>Graham, S. A., and L. A. Williams, 1985, [http://archives.datapages.com/data/bulletns/1984-85/data/pg/0069/0003/0350/0385.htm Tectonic, depositional, and diagenetic history of Monterey Formation (Miocene), central San Juaquin Basin, California]: AAPG Bulletin, v. 69, p. 385-411.</ref>
==Structure==
==Structure==
The oil accumulation at Yowlumne is controlled in part by an anticlinal closure formed during Miocene-Pliocene deformation of the south basin margin. Yowlumne Unit A was created to waterflood the area of structural closure, but subsequent drilling established production in a stratigraphic accumulation on the north-dipping flank of the anticline also ([[:file:Mth14ch02f01.jpg|Figure 1]]). Consequently, Yowlumne Unit B was created to flood the flank accumulation (Burzlaff,<ref name=Burzlaff_1983>Burzlaff,</ref> Metz and Whitworth<ref name=Metzandwhitworth_1984>Metz,</ref>). Thus, the field is a combination structural-stratigraphic trap.
The oil accumulation at Yowlumne is controlled in part by an anticlinal closure formed during Miocene-Pliocene deformation of the south basin margin. Yowlumne Unit A was created to waterflood the area of structural closure, but subsequent drilling established production in a stratigraphic accumulation on the north-dipping flank of the anticline also ([[:file:Mth14ch02f01.jpg|Figure 1]]). Consequently, Yowlumne Unit B was created to flood the flank accumulation (Burzlaff,<ref name=Burzlaff_1983>Burzlaff, A. A., 1983, Unitizing and waterflooding the California Yowlumne oil field: Society of Petroleum Engineers, SPE 11685, p. 187-194.</ref> Metz and Whitworth<ref name=Metzandwhitworth_1984>Metz, R. T., and J. L. Whitworth, 1984, Yowlumne oil field, ''in'' G. W. Kendall and S. C. Kiser, eds., Selected papers presented to San Joaquin Geological Society, v. 6, p. 3-23.</ref>). Thus, the field is a combination structural-stratigraphic trap.
<gallery mode=packed heights=300px widths=300px>
<gallery mode=packed heights=300px widths=300px>
file:mth14ch02f03.jpg|{{figure number|3}}Type log for Yowlumne field with reservoir statistics and rock properties of the Yowlumne Sandstone. Reservoir quality decreases from the axis of the fan eastward toward the fan margin.
file:mth14ch02f03.jpg|{{figure number|3}}Type log for Yowlumne field with reservoir statistics and rock properties of the Yowlumne Sandstone. Reservoir quality decreases from the axis of the fan eastward toward the fan margin.
file:Mth14ch02f04.jpg|{{figure number|4}}Seismic line and cross section A-A' showing left-stepping geometries and cross-sectional lens shape of the Yowlumne fan. The line and section transect the fan from west to east, perpendicular to the direction of sediment transport.
file:Mth14ch02f04.jpg|{{figure number|4}}Seismic line and cross section A-A' showing left-stepping geometries and cross-sectional lens shape of the Yowlumne fan. The line and section transect the fan from west to east, perpendicular to the direction of sediment transport.
file:Mth14ch02f05.jpg|{{figure number|5}} Map with cross sections X-Z and Y-Z showing basinward-stepping geometries exhibited by lobe-shaped sand bodies that make up the Yowlumne Sandstone. Note 660 m (2100 ft) of structural relief between oil-water contacts in the lobes of Units A and B.
</gallery>
</gallery>
Thin shales divide the fan into lobe-shaped reservoir layers ([[:file:Mth14ch02f04.jpg|Figure 4]]). Five of these—the A, B, C, D, and E sands—produce oil from Unit B. The W sand is a basal sixth layer that is wet and isolated by pressure from over-lying sandstones. Layers A through E merge into homogenous, clean sandstone on the west margin of the fan, yet contain interbedded shale on the east. For example, the 16x-4 [[horizontal well]] on the west side ([[:file:Mth14ch02f01.jpg|Figure 1]]) penetrates a thick interval of clean sandstone (Marino and Schultz<ref name=Marinoandschultz_1992>Marino,</ref>). By contrast, the 73x-3 well on the east side ([[:file:Mth14ch02f01.jpg|Figure 1]]) penetrates shale layers, some of which are two or more meters thick, interbedded with the reservoir sandstones.
Thin shales divide the fan into lobe-shaped reservoir layers ([[:file:Mth14ch02f04.jpg|Figure 4]]). Five of these—the A, B, C, D, and E sands—produce oil from Unit B. The W sand is a basal sixth layer that is wet and isolated by pressure from over-lying sandstones. Layers A through E merge into homogenous, clean sandstone on the west margin of the fan, yet contain interbedded shale on the east. For example, the 16x-4 [[horizontal well]] on the west side ([[:file:Mth14ch02f01.jpg|Figure 1]]) penetrates a thick interval of clean sandstone (Marino and Schultz<ref name=Marinoandschultz_1992>Marino, A. W., and S. M. Schultz, 1992, Case study of Stevens sand horizontal well: Society of Petroleum Engineers, SPE 24910, p. 549-563.</ref>). By contrast, the 73x-3 well on the east side ([[:file:Mth14ch02f01.jpg|Figure 1]]) penetrates shale layers, some of which are two or more meters thick, interbedded with the reservoir sandstones.
Well-log
Well-log correlations and 3-D seismic data indicate downlap within the fan, with basinward progradation to the north and lateral progradation to the west ([[:file:M14ch02f04.jpg|Figure 4]], [[:file:M14ch02f05.jpg|Figure 5]]). In other words, lobe-shaped, shale-bounded reservoir layers in Unit B step to the left when facing basinward, in the direction of sediment transport (Jessup and Kamerling<ref name=Jessupandkamerling_1991>Jessup,</ref>
==References==
==References==