10,370
edits
Changes
Jump to navigation
Jump to search
Line 15:
Line 15: − + Line 112:
Line 112: − + + + − − [[file:fluid-contacts_fig2.png|thumb|{{figure number|2}}Geometries of fluid contacts. (a) Horizontal contacts indicative of hydrostatic conditions in homogeneous reservoir rock. (b) Tilted, flat contacts resulting from hydrodynamic conditions. (c) Contact elevation is constant for each lithology type, but pool contact is irregular due to reservoir heterogeneity. (d) Irregular contacts due to semipermeable barrier in an otherwise homogeneous reservoir.]]
no edit summary
Positions of initial fluid contacts are critical for field reserve estimates and for field development. Typically, the position of fluid contacts are first determined within control wells and then extrapolated to other parts of the field.
Positions of initial fluid contacts are critical for field reserve estimates and for field development. Typically, the position of fluid contacts are first determined within control wells and then extrapolated to other parts of the field.
Definitions of fluid contacts are based on comparison to [[capillary pressure]] curves (Figure 1) (see [[Capillary pressure]]). The ''free water surface'' is the highest elevation at which the pressure of the hydrocarbon phase is the same as that of water. The ''hydrocarbon-water'' (''oil-water'' or ''gas-water'') ''contact'' is the lowest elevation at which mobile hydrocarbons occur. The ''transition zone'' is the elevation range in which water is coproduced with hydrocarbons. The ''gas-oil contact'' is the elevation above which gas is the produced hydrocarbon phase.
Definitions of fluid contacts are based on comparison to [[capillary pressure]] curves ([[:file:fluid-contacts_fig1.png|Figure 1]]) (see [[Capillary pressure]]). The ''free water surface'' is the highest elevation at which the pressure of the hydrocarbon phase is the same as that of water. The ''hydrocarbon-water'' (''oil-water'' or ''gas-water'') ''contact'' is the lowest elevation at which mobile hydrocarbons occur. The ''transition zone'' is the elevation range in which water is coproduced with hydrocarbons. The ''gas-oil contact'' is the elevation above which gas is the produced hydrocarbon phase.
[[file:fluid-contacts_fig1.png|thumb|{{figure number|1}}Contact definitions and relationship of contacts in a pool (right) to reservoir capillary pressure and fluid production curves (left). The free water surface is the highest elevation with the same oil and water pressure (zero capillary pressure). The oil-water contact corresponds to the displacement pressure (DP) on the capillary pressure curve. The transition zone is the interval with co-production of water and hydrocarbons. The fraction of co-produced water is shown by the dashed line on the left. The gas-oil contact is controlled by the volume of gas in the trap, not the capillary properties.]]
[[file:fluid-contacts_fig1.png|thumb|{{figure number|1}}Contact definitions and relationship of contacts in a pool (right) to reservoir capillary pressure and fluid production curves (left). The free water surface is the highest elevation with the same oil and water pressure (zero capillary pressure). The oil-water contact corresponds to the displacement pressure (DP) on the capillary pressure curve. The transition zone is the interval with co-production of water and hydrocarbons. The fraction of co-produced water is shown by the dashed line on the left. The gas-oil contact is controlled by the volume of gas in the trap, not the capillary properties.]]
|}
|}
Some reservoirs have irregular or tilted fluid contacts (Figure 2). Reasons for differences in contact elevation in different control wells must first be determined to properly extrapolate nonhorizontal fluid contacts to untested parts of a reservoir. Excluding interpretation or mechanical problems, the most common reasons for tilted fluid contacts are the following:
[[file:fluid-contacts_fig2.png|thumb|{{figure number|2}}Geometries of fluid contacts. (a) Horizontal contacts indicative of hydrostatic conditions in homogeneous reservoir rock. (b) Tilted, flat contacts resulting from hydrodynamic conditions. (c) Contact elevation is constant for each lithology type, but pool contact is irregular due to reservoir heterogeneity. (d) Irregular contacts due to semipermeable barrier in an otherwise homogeneous reservoir.]]
Some reservoirs have irregular or tilted fluid contacts ([[:file:fluid-contacts_fig2.png|Figure 2]]). Reasons for differences in contact elevation in different control wells must first be determined to properly extrapolate nonhorizontal fluid contacts to untested parts of a reservoir. Excluding interpretation or mechanical problems, the most common reasons for tilted fluid contacts are the following:
* Hydrodynamic gradients
* Hydrodynamic gradients
* Reservoir heterogeneity (see [[Geological heterogeneities]])
* Reservoir heterogeneity (see [[Geological heterogeneities]])
* Semipermeable barriers
* Semipermeable barriers
Situations can usually be distinguished because they are associated with different geological settings and result in different fluid contact characteristics (Table 2).
Situations can usually be distinguished because they are associated with different geological settings and result in different fluid contact characteristics (Table 2).