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[[File:BasinCenteredGasFig14.jpg|thumb|300px|{{figure number|4}}Thermal maturity map of the Denver basin, Colorado, showing the large thermal maturity anomaly in the Cretaceous Muddy ("J") Sandstone in the Wattenburg field (modified from Higley et al.<ref name=Higleyetal_1992 />). The field is nearly coincident with the 0.9% isoreflectance [[contour]].<ref name=Higleyetal_1992 /> The location of the anomaly is also coincident with the basinward projection of the Colorado Mineral Belt (CMB).]]

[[File:BasinCenteredGasFig14.jpg|thumb|300px|{{figure number|4}}Thermal maturity map of the Denver basin, Colorado, showing the large thermal maturity anomaly in the Cretaceous Muddy ("J") Sandstone in the Wattenburg field (modified from Higley et al.<ref name=Higleyetal_1992 />). The field is nearly coincident with the 0.9% isoreflectance [[contour]].<ref name=Higleyetal_1992 /> The location of the anomaly is also coincident with the basinward projection of the Colorado Mineral Belt (CMB).]]

A good example of a thermal maturity anomaly associated with a sweet spot is the Lower Cretaceous Muddy ("J") Sandstone in the Denver basin of Colorado. Regional thermal maturity mapping in the Denver basin of Colorado<ref name=Higleyetal_1992>Higley, D. K., D. L. Gautier, and M. J. Pawlewicz, 1992, Influence of regional heat flow variation on thermal maturity of the Lower Cretaceous Muddy ("J") Sandstone, Denver basin, Colorado, ''in'' The petroleum system-status of research and methods, 1992: U.S. Geological Survey Bulletin 2007, p. 66-69.</ref> shows the presence of an anomaly associated with a BCGA ([[:file:BasinCenteredGasFig14.jpg|Figure 4]]). The anomaly, defined by reflectance values greater than 0.9% R_o, is nearly coincident with the field boundaries of production from the Muddy Sandstone in the Wattenburg field. The anomaly is located north of the structurally deepest part of the basin and is coincident with the northeast projection of the Colorado Mineral Belt. The field is also coincident with a temperature anomaly mapped by Meyer and McGee.<ref name=Meyerandmcgee_1985>Meyer, H. J., and H. W. McGee, 1985, [http://archives.datapages.com/data/bulletns/1984-85/data/pg/0069/0006/0900/0933.htm Oil and gas fields accompanied by geothermal anomalies in the Rocky Mountain region]: AAPG Bulletin, v. 69, p. 933-945.</ref>

A good example of a thermal maturity anomaly associated with a sweet spot is the Lower Cretaceous Muddy ("J") Sandstone in the Denver basin of Colorado. Regional thermal maturity mapping in the Denver basin of Colorado<ref name=Higleyetal_1992>Higley, D. K., D. L. Gautier, and M. J. Pawlewicz, 1992, Influence of regional heat flow variation on thermal maturity of the Lower Cretaceous Muddy ("J") Sandstone, Denver basin, Colorado, ''in'' The petroleum system-status of research and methods, 1992: U.S. Geological Survey Bulletin 2007, p. 66-69.</ref> shows the presence of an anomaly associated with a BCGA ([[:file:BasinCenteredGasFig14.jpg|Figure 4]]). The anomaly, defined by reflectance values greater than 0.9% R_o (for better understanding of reflectance values correlation you can look at [http://thetermpapers.net thetermpapers.net]), is nearly coincident with the field boundaries of production from the Muddy Sandstone in the Wattenburg field. The anomaly is located north of the structurally deepest part of the basin and is coincident with the northeast projection of the Colorado Mineral Belt. The field is also coincident with a temperature anomaly mapped by Meyer and McGee.<ref name=Meyerandmcgee_1985>Meyer, H. J., and H. W. McGee, 1985, [http://archives.datapages.com/data/bulletns/1984-85/data/pg/0069/0006/0900/0933.htm Oil and gas fields accompanied by geothermal anomalies in the Rocky Mountain region]: AAPG Bulletin, v. 69, p. 933-945.</ref>

Because the top of a BCGA is determined, in part, by permeability variations and the ease with which gas may move through reservoirs, measured levels of thermal maturity at the top of a BCGA may provide indirect evidence of the presence of a sweet spot; relatively low values of thermal maturity (<0.8% R_o) at the top of an overpressured BCGA are indicative of a potential sweet spot, whereas relatively high values of thermal maturity (>0.8% R_o) are indicative of very low permeability in an overpressured BCGA. Based on vitrinite reflectance profiles from two wells within the Jonah field,<ref name=Warner_1998 /> the level of thermal maturity at the top of overpressured, gas-saturated reservoirs is less than 0.7% R_o, compared to 0.8% R_o outside the field. Thermal maturity indices, however, cannot be used to identify potential sweet spots in underpressured BCGAs. The level of thermal maturity at the top of an underpressured BCGA most likely is higher than the level of thermal maturity at the top of an overpressured BCGA because the dimensions, or size, of a BCGA are reduced during the transition from overpressure to underpressure. Consequently, the level of thermal maturity at the top of an underpressured BCGA reflects that size constriction.

Because the top of a BCGA is determined, in part, by permeability variations and the ease with which gas may move through reservoirs, measured levels of thermal maturity at the top of a BCGA may provide indirect evidence of the presence of a sweet spot; relatively low values of thermal maturity (<0.8% R_o) at the top of an overpressured BCGA are indicative of a potential sweet spot, whereas relatively high values of thermal maturity (>0.8% R_o) are indicative of very low permeability in an overpressured BCGA. Based on vitrinite reflectance profiles from two wells within the Jonah field,<ref name=Warner_1998 /> the level of thermal maturity at the top of overpressured, gas-saturated reservoirs is less than 0.7% R_o, compared to 0.8% R_o outside the field. Thermal maturity indices, however, cannot be used to identify potential sweet spots in underpressured BCGAs. The level of thermal maturity at the top of an underpressured BCGA most likely is higher than the level of thermal maturity at the top of an overpressured BCGA because the dimensions, or size, of a BCGA are reduced during the transition from overpressure to underpressure. Consequently, the level of thermal maturity at the top of an underpressured BCGA reflects that size constriction.