Changes

* Pay versus nonpay

* Pay versus nonpay

* Expected fluid saturations

* Expected fluid saturations

* Seal capacity (thickness of hydrocarbon column a seal can hold before it leaks)

* Seal capacity (thickness of [[hydrocarbon column]] a seal can hold before it leaks)

* Depth of the reservoir [[fluid contacts]]

* Depth of the reservoir [[fluid contacts]]

* Thickness of the transition zone

* Thickness of the transition zone

These equations show that capillary pressure increases with greater height above the free surface and with smaller capillary size.

These equations show that capillary pressure increases with greater height above the free surface and with smaller capillary size.

The importance of capillary pressure in reservoir studies is that many reservoir rocks can be approximated by a bundle of capillaries, with formation water being the wetting phase and hydrocarbons the nonwetting phase. As hydrocarbons begin to migrate into a rock, displacing the pore water, the hydrocarbons first enter the pores with the largest pore throats (capillaries), leaving the wetting phase (water) in the pores with smaller throats or in small nooks and crannies (surface roughness). As the hydrocarbon column increases, the height above the surface where ''P''_c = 0, called the free surface or ''free water level'' (FWL), becomes greater and the capillary pressure increases, allowing hydrocarbons to enter pores with smaller and smaller throats. This process continues until one of several things occurs:

The importance of capillary pressure in reservoir studies is that many reservoir rocks can be approximated by a bundle of capillaries, with formation water being the wetting phase and hydrocarbons the nonwetting phase. As hydrocarbons begin to migrate into a rock, displacing the pore water, the hydrocarbons first enter the pores with the largest pore throats (capillaries), leaving the wetting phase (water) in the pores with smaller throats or in small nooks and crannies (surface roughness). As the hydrocarbon column increases, the height above the surface where ''P''_c = 0, called the free surface or ''[[free water level]]'' (FWL), becomes greater and the capillary pressure increases, allowing hydrocarbons to enter pores with smaller and smaller throats. This process continues until one of several things occurs:

# [[Petroleum generation|generation]] or migration ends,

# [[Petroleum generation|generation]] or migration ends,

# the trap reaches its spill point, or

# the trap reaches its spill point, or

| [[Crude oil]]–water || 0° || 35

| [[Crude oil]]–water || 0° || 35

|}

|}

''<small>* Contact angle is measured on a quartz plane during drainage</small>''

''<small>* Contact angle is measured on a [[quartz]] plane during drainage</small>''

{| class="wikitable"

{| class="wikitable"

[[Category:Laboratory methods]]

[[Category:Laboratory methods]]