Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Predicting reservoir system quality and performance

  | chapter = Predicting reservoir system quality and performance

  | frompg  = 9-1

  | frompg  = 9-131

  | topg    = 9-156

  | topg    = 9-134

  | author  = Dan J. Hartmann, Edward A. Beaumont

  | author  = Dan J. Hartmann, Edward A. Beaumont

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm

==Well 11 flow units==

==Well 11 flow units==

[[file:predicting-reservoir-system-quality-and-performance_fig9-90.png|thumb|{{figure number|1}}. Copyright: Hartmann and Coalson, 1990; courtesy RMAG.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-90.png|300px|thumb|{{figure number|1}}From Hartmann and Coalson.<ref name=Hartmannandcoalson_1990>Hartmann, D. J., and E. B. Coalson, 1990, Evaluation of the Morrow sandstone in Sorrento field, Cheyenne County, Colorado, ''in'' S. A. Sonnenberg, L. T. Shannon, K. Rader, W. F. von Drehle, and G.W. Martin, eds., Morrow Sandstones of Southeast Colorado and Adjacent Areas: RMAG Symposium, p. 91-100.</ref> Courtesy Rocky Mountain Association of Geologists.]]

Flow units were determined in well 11 by plotting and grouping routine core data. The top and bottom of the Morrow (flow units A and 5) are microporous, low-[[permeability]] sandstones that are wet but too tight to produce. Between these are [[length::30 ft]] [[depth::(8.5 m]]) of mesoto macroporous sandstone (flow units 1-4).

Flow units were determined in well 11 by plotting and grouping routine [[Overview of routine core analysis|core data]]. The top and bottom of the Morrow (flow units A and 5) are microporous, low-[[permeability]] sandstones that are wet but too tight to produce. Between these are [[length::30 ft]] [[depth::(8.5 m]]) of mesoto macroporous sandstone (flow units 1-4).

All pertinent petrophysical data for well 11 are summarized on [[:file:predicting-reservoir-system-quality-and-performance_fig9-90.png|Figure 1]]. Sandstone descriptors found on [[porosity]] logs are as follows:

All pertinent petrophysical data for well 11 are summarized on [[:file:predicting-reservoir-system-quality-and-performance_fig9-90.png|Figure 1]]. Sandstone descriptors found on [[porosity]] logs are as follows:

==Well 11 water saturations==

==Well 11 water saturations==

[[file:predicting-reservoir-system-quality-and-performance_fig9-91.png|thumb|{{figure number|2}}. Copyright: Hartmann and Coalson, 1990; courtesy RMAG.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-91.png|300px|thumb|{{figure number|2}}From Hartmann and Coalson.<ref name=Hartmannandcoalson_1990 /> Courtesy Rocky Mountain Association of Geologists.]]

Flow unit 4 is macroporous but wet (S_w = 100%); this indicates an oil-water contact. Flow unit 3 is macroporous and has intermediate water saturation (S_w = 70%). This looks like a transition zone. Flow units 2 and 1 are mesoporous and are at immobile water saturation (S_w = 45%). This is verified by the well testing about 100 bo/d and 300 Mcfg/d (16 m³ oil and 8,500 m³gas per day) with no water from perforations in these flow units and by a bulk-volume-water plot following. This lack of water production is remarkable, considering that the well lies only about [[length::25 ft]] (7 m) above the [[free water level]].

Flow unit 4 is macroporous but wet (S_w = 100%); this indicates an [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=oil-water%20contact oil-water contact]. Flow unit 3 is macroporous and has intermediate water saturation (S_w = 70%). This looks like a transition zone. Flow units 2 and 1 are [[Wikipedia:Mesoporous material|mesoporous]] and are at immobile water saturation (S_w = 45%). This is verified by the well testing about 100 bo/d and 300 Mcfg/d (16 m³ oil and 8,500 m³gas per day) with no water from perforations in these flow units and by a bulk-volume-water plot following. This lack of water production is remarkable, considering that the well lies only about [[length::25 ft]] (7 m) above the [[free water level]].

[[:file:predicting-reservoir-system-quality-and-performance_fig9-91.png|Figure 2]] is the bulk-volume-water (Buckles) plot for well 11.

[[:file:predicting-reservoir-system-quality-and-performance_fig9-91.png|Figure 2]] is the bulk-volume-water ([[Buckles plot|Buckles]]) plot for well 11.

==Well 4==

==Well 4==

[[file:predicting-reservoir-system-quality-and-performance_fig9-92.png|thumb|{{figure number|3}}. Copyright: Hartmann and Coalson, 1990; courtesy RMAG.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-92.png|300px|thumb|{{figure number|3}}From Hartmann and Coalson.<ref name=Hartmannandcoalson_1990 /> Courtesy Rocky Mountain Association of Geologists.]]

Well 4 hit the Morrow near the top of the oil column. It had the lowest saturations and best flow rates of all the wells studied, even though it had the thinnest reservoir. This is because it contained rock with large pore throats (r₃₅ up to 50μ) that was fully saturated with oil (S_w = 25-30%). The well tested 230 bo/d and 387 Mcfg/d (37 m³ oil and 11,000 m³ gas per day). Initial production was 51 bo/d and 411 Mcfg/d (8 m³ oil and 12,000 m³ gas per day). The difference could be due to a loss of reservoir thickness near the well bore, judging from the thinness of the reservoir.

Well 4 hit the Morrow near the top of the oil column. It had the lowest saturations and best flow rates of all the wells studied, even though it had the thinnest reservoir. This is because it contained rock with large pore throats ([[Characterizing_rock_quality#What_is_r35.3F|r₃₅]] up to 50μ) that was fully saturated with oil (S_w = 25-30%). The well tested 230 bo/d and 387 Mcfg/d (37 m³ oil and 11,000 m³ gas per day). Initial production was 51 bo/d and 411 Mcfg/d (8 m³ oil and 12,000 m³ gas per day). The difference could be due to a loss of reservoir thickness near the well bore, judging from the thinness of the reservoir.

[[:file:predicting-reservoir-system-quality-and-performance_fig9-92.png|Figure 3]] summarizes the petrophysical characteristics of well 4.

[[:file:predicting-reservoir-system-quality-and-performance_fig9-92.png|Figure 3]] summarizes the petrophysical characteristics of well 4.

==Well 8==

==Well 8==

[[file:predicting-reservoir-system-quality-and-performance_fig9-93.png|thumb|{{figure number|4}}. Copyright: Hartmann and Coalson, 1990; courtesy RMAG.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-93.png|thumb|300px|{{figure number|4}}From Hartmann and Coalson.<ref name=Hartmannandcoalson_1990 /> Courtesy Rocky Mountain Association of Geologists.]]

Wells 8 and 1 both are interpreted as encountering transition zones, based on porosity types and log-calculated saturations. Well 8 encountered the Morrow just above the water level. Pore throats are meso- to macroporous. The two upper flow units probably are close to immobile water saturation. However, the two basal zones (3 and 4) have high saturations of mobile water. This explains why the well cut water on initial potential testing. This water production should increase with time as the water leg rises.

Wells 8 and 1 both are interpreted as encountering transition zones, based on porosity types and log-calculated saturations. Well 8 encountered the Morrow just above the water level. Pore throats are meso- to macroporous. The two upper flow units probably are close to immobile water saturation. However, the two basal zones (3 and 4) have high saturations of mobile water. This explains why the well cut water on initial potential testing. This water production should increase with time as the water leg rises.

==Well 1==

==Well 1==

Well 1 is similar to well 8, except that flow unit 2 of well 1 shows an anomalous low resistivity. The interval tested 32 bo/d and 15 Mcfg/d (5 m³ oil and 425 m³ gas per day) with no water. Therefore, the zone by definition is at immobile water saturation (S_wi = 40%). The discrepancy suggests that the log resistivity was too low due to bed resolution problems. If true resistivity is 9 ohm-m²/m (used for the calculation), then the true water saturation is less than 40%.

Well 1 is similar to well 8, except that flow unit 2 of well 1 shows an anomalous low resistivity. The interval tested 32 bo/d and 15 Mcfg/d (5 m³ oil and 425 m³ gas per day) with no water. Therefore, the zone by definition is at immobile water saturation (S_wi = 40%). The discrepancy suggests that the log resistivity was too low due to bed resolution problems. If true resistivity is 9 ohm-m²/m (used for the calculation), then the true water saturation is less than 40%.

==Caveat==

==Caveat==

While these petrophysical methods of analyzing wells are reliable and widely applicable in water-wet reservoirs, there is at least one source of potential error: the assumption that there are no lithologic changes that affect log-calculation parameters without affecting permeability-porosity relationships. Examples include vuggy or fracture porosity and variable shale effects. If such changes occur, then we must modify the relationships between calculated saturations and producibility.

While these petrophysical methods of analyzing wells are reliable and widely applicable in water-wet reservoirs, there is at least one source of potential error: the assumption that there are no lithologic changes that affect log-calculation parameters without affecting permeability-porosity relationships. Examples include vuggy or [[fracture]] porosity and variable shale effects. If such changes occur, then we must modify the relationships between calculated saturations and producibility.

==See also==

==See also==

* [[Sorrento water saturation calculations]]

* [[Sorrento water saturation calculations]]

* [[Water saturation profile for Sorrento field]]

* [[Water saturation profile for Sorrento field]]

==External links==

==External links==

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting reservoir system quality and performance]]

[[Category:Predicting reservoir system quality and performance]]