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  = 9-40

  | topg    = 9-156

  | topg    = 9-43

  | 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

==Why k_ro or k_rg is less than k_ab==

==Why k_ro or k_rg is less than k_ab==

[[file:predicting-reservoir-system-quality-and-performance_fig9-26.png|thumb|{{figure number|1}}See text for explanation.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-26.png|300px|thumb|{{figure number|1}}When a sample contains oil or gas and water (where water wets the grain surface), the pore throat size (B) for oil or gas flow is less than the absolute pore throat size (A). The thickness of the water layer coating the grains is proportional to the S_w of the rock. In other words, as [[buoyancy pressure]] increases, S_w decreases and the effective size of the pore throat for oil or gas flow (B) increases.]]

A pore system saturated 100% with any fluid transmits that fluid at a rate relative to the pore throat size and the pressure differential. In the drawing in [[:file:predicting-reservoir-system-quality-and-performance_fig9-26.png|Figure 1]], the absolute pore throat size (A) is noted as the distance between grain surfaces. When a sample contains oil or gas and water (where water wets the grain surface), the pore throat size (B) for oil or gas flow is less than the absolute pore throat size (A). The thickness of the water layer coating the grains is proportional to the S_w of the rock. In other words, as [[buoyancy pressure]] increases, S_w decreases and the effective size of the pore throat for oil or gas flow (B) increases.

A pore system saturated 100% with any fluid transmits that fluid at a rate relative to the pore throat size and the pressure differential. In the drawing in [[:file:predicting-reservoir-system-quality-and-performance_fig9-26.png|Figure 1]], the absolute pore throat size (A) is noted as the distance between grain surfaces. When a sample contains oil or gas and water (where water wets the grain surface), the pore throat size (B) for oil or gas flow is less than the absolute pore throat size (A). The thickness of the water layer coating the grains is proportional to the S_w of the rock. In other words, as [[buoyancy pressure]] increases, S_w decreases and the effective size of the pore throat for oil or gas flow (B) increases.

==Interpreting a relative permeability curve==

==Interpreting a relative permeability curve==

[[file:predicting-reservoir-system-quality-and-performance_fig9-27.png|thumb|{{figure number|2}} Modified.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-27.png|300px|thumb|{{figure number|2}}Three relative permeability curves. Modified from Arps.<ref name=Arps_1964>Arps, J. J. 1964, [http://archives.datapages.com/data/bulletns/1961-64/data/pg/0048/0002/0150/0157.htm Engineering concepts useful in oil finding]: AAPG Bulletin, v. 48, no. 2, p. 943-961.</ref>]]

The diagram in [[:file:predicting-reservoir-system-quality-and-performance_fig9-27.png|Figure 2]] shows relationships between relative permeability curves (drainage and imbibition), [[capillary pressure]], and fluid distribution in a homogeneous section of a reservoir system. The reservoir system rock has a [[porosity]] of 30% and a permeability of 10 md (r₃₅ = 1.1μ). Laboratory single-phase air permeability is typically used to represent absolute permeability (K_a when determining relative permeability to oil or water at a specific S_w.

The diagram in [[:file:predicting-reservoir-system-quality-and-performance_fig9-27.png|Figure 2]] shows relationships between relative permeability curves (drainage and imbibition), [[capillary pressure]], and fluid distribution in a homogeneous section of a reservoir system. The reservoir system rock has a [[porosity]] of 30% and a permeability of 10 md ([[Characterizing_rock_quality#What_is_r35.3F|r₃₅]] = 1.1μ). Laboratory single-phase air permeability is typically used to represent absolute permeability (K_a when determining relative permeability to oil or water at a specific S_w.

[[: [[:file:predicting-reservoir-system-quality-and-performance_fig9-27.png|Figure 2]] depicts three relative permeability curves:

[[:file:predicting-reservoir-system-quality-and-performance_fig9-27.png|Figure 2]] depicts three relative permeability curves:

* Water (K_rw)—similar for both drainage and imbibition tests

* Water (K_rw)—similar for both drainage and imbibition tests

Consider points A–D below. Point A, at S_w = 100%, is the original condition of the sample. Here K_rw ≈ K_a (10 md). At point B (S_w ≈ 90%, S₀ = 10%), oil breaks through the sample, representing the [[migration]] saturation of the sample; K_ro = 1.0. At point C (S_w ≈ 50%, S_o ≈ 10%), K_rw is less than 1% of K_a and water, now confined to only the smallest ports, ceases to flow while oil flow approaches its maximum. At point D on the K_ro-D curve (S_w ≈ 20%, S_o ≈ 80%), relative permeability is approaching 1.0 (~ 10 md).

Consider points A–D below. Point A, at S_w = 100%, is the original condition of the sample. Here K_rw ≈ K_a (10 md). At point B (S_w ≈ 90%, S₀ = 10%), oil breaks through the sample, representing the [[migration]] saturation of the sample; K_ro = 1.0. At point C (S_w ≈ 50%, S_o ≈ 10%), K_rw is less than 1% of K_a and water, now confined to only the smallest ports, ceases to flow while oil flow approaches its maximum. At point D on the K_ro-D curve (S_w ≈ 20%, S_o ≈ 80%), relative permeability is approaching 1.0 (~ 10 md).

[[:file:predicting-reservoir-system-quality-and-performance_fig9-27.png|Figure 2]] is an example of “drainage” relative permeability of a water-wet reservoir. It shows changes in K_ro and K_rw as S_w decreases, as in a water-drive reservoir during hydrocarbon fill-up. “Imbibition” K_ro and K_rw have a different aspect, being measured while S_w increases, as it does during production in a reservoir with a water drive.

[[:file:predicting-reservoir-system-quality-and-performance_fig9-27.png|Figure 2]] is an example of “drainage” relative permeability of a water-wet reservoir. It shows changes in K_ro and K_rw as S_w decreases, as in a water-drive reservoir during hydrocarbon fill-up. “Imbibition” K_ro and K_rw have a different aspect, being measured while S_w increases, as it does during production in a reservoir with a water drive.

==Drainage vs. imbibition curves==

==Drainage vs. imbibition curves==

==Pore throat size and k_r==

==Pore throat size and k_r==

Every pore type has a unique relative permeability signature. Consider the hypothetical drainage relative permeability type curves shown below. Curves A, B, and C represent the relative permeability relationships for rocks with different port types: macro, meso, and micro, respectively. Curve A represents a rock with greater performance capability than B or C. Note how critical water saturation decreases as pore throat size increases. Also note the changing position of K_ro–K_rw crossover with changes in pore throat size.

 

 

Every pore type has a unique relative permeability signature. Consider the hypothetical drainage relative permeability type curves shown in [[:file:predicting-reservoir-system-quality-and-performance_fig9-28.png|Figure 3]]. Curves A, B, and C represent the relative permeability relationships for rocks with different pore types: macro, [[Wikipedia:Mesoporous material|meso]], and micro, respectively. Curve A represents a rock with greater performance capability than B or C. Note how critical water saturation decreases as pore throat size increases. Also note the changing position of K_ro–K_rw crossover with changes in pore throat size.

==Critical water saturation==

==Critical water saturation==

==Critical water saturation==

==Critical water saturation==

The critical S_w value is different for each port type. Curve A in Figure 9-28 represents rocks with macroporosity. It has a critical S_w less than 20%. Curve B represents a rock (continued) with [[Wikipedia:Mesoporous material|mesoporosity]]. Mesoporous rocks have a critical S_w of 20–60%. Curve C represents rocks with microporosity. They have a critical S_w of 60–80%.

 

The critical S_w value is different for each port type. Curve A in Figure 9-28 represents rocks with macroporosity. It has a critical S_w less than 20%. Curve B represents a rock (continued) with mesoporosity. Mesoporous rocks have a critical S_w of 20–60%. Curve C represents rocks with microporosity. They have a critical S_w of 60–80%.

The table below summarizes representative critical S_w values for macro-, meso-, and micropore types that correspond to A, B, and C, respectively, in [[:file:predicting-reservoir-system-quality-and-performance_fig9-28.png|Figure 3]].

The table below summarizes representative critical S_w values for macro-, meso-, and micropore types that correspond to A, B, and C, respectively, in [[:file:predicting-reservoir-system-quality-and-performance_fig9-28.png|Figure 3]].

==See also==

==See also==

* [[Pore–fluid interaction]]

* [[Pore-fluid interaction]]

* [[Hydrocarbon expulsion, migration, and accumulation]]

* [[Hydrocarbon expulsion, migration, and accumulation]]

* [[Characterizing rock quality]]

* [[Characterizing rock quality]]

* [[Converting Pc curves to buoyancy, height, and pore throat radius]]

* [[Converting Pc curves to buoyancy, height, and pore throat radius]]

* [[What is permeability?]]

* [[What is permeability?]]

==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]]