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Line 34: − 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. Line 40:
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file:Mth14ch02f01.jpg|{{figure number|1}}Structure map of Yowlumne field drawn on the N-point marker, a regional correlation horizon that marks the approximate top of the Stevens Sandstone. Note the fanlike shape of the Yowlumne Sandstone and the relationship of Yowlumne Units A and B to the anticlinal closure.
file:Mth14ch02f01.jpg|{{figure number|1}}Structure map of Yowlumne field drawn on the N-point marker, a regional correlation horizon that marks the approximate top of the Stevens Sandstone. Note the fanlike shape of the Yowlumne Sandstone and the relationship of Yowlumne Units A and B to the anticlinal closure.
file:Mthch02f02.jpg|{{figure number|2}}Stratigraphic section showing nomenclature for the Yowlumne field area. The Stevens is an informal unit that represents a deep-marine, clastic facies of the Monterey Formation, an organic-rich shale that is considered to be the main source rock for most of the oil produced from the basin.
file:Mthch02f02.jpg|{{figure number|2}}Stratigraphic section showing nomenclature for the Yowlumne field area. The Stevens is an informal unit that represents a deep-marine, clastic facies of the Monterey Formation, an organic-rich shale that is considered to be the main source rock for most of the oil produced from the basin.
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.
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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.
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.
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.
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 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>
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:Mth14ch02f04.jpg|Figure 4]], [[:file:Mth14ch02f05.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, D. D., and M. Kamerling, 1991, [http://www.searchanddiscovery.com/abstracts/html/1991/pacific/abstracts/0368b.htm Depositional style of the Yowlumne sands, Yowlumne oil field, southern San Joaquin Basin, California] (abs.): AAPG Bulletin, v. 75, p. 368.</ref> Clark et al.<ref name=Clarketal_1996b>Clark, M. S., J. Melvin, and M. Kamerling, 1996, [http://www.searchanddiscovery.com/abstracts/html/1996/annual/abstracts/0027.htm Growth patterns of a Miocene turbidite complex in an active-margin basin, Yowlumne field, San Joaquin Basin, California] (abs.): AAPG Annual Convention Official Program, San Diego, 1996, v. 5, p. A27.</ref>). Thus, the basal productive layer (sand E) is thickest on the right (east) side of the fan, whereas the top layer (sand A) is thickest on the left (west).
Variations in reservoir pressures and injection of radioactive tracers indicate weak compartmentalization of the reservoir, which results in separate permeability pathways along which fluids flow at different rates (Metz and Whitworth, their figure 9;<ref name=Metzandwhitworth_1984>Metz,</ref> Berg and Royo<ref name=Bergandroyo_1990>Berg,</ref>). Most likely, these pathways represent different flow units that, for the most part, are in pressure communication over geologic time. Consequently, these compartments, which correlate to the shale-bounded, lobe-shaped reservoir layers already discussed, develop the same [[oil-water contact]] over thousands of years yet acquire slightly different pressures as the field is rapidly produced over tens of years.
==References==
==References==