Subsurface Waters
Types of subsurface water by their mode of occurrence
1. FREE WATER
Free to move in and out of pores to response a pressure differential.
2. INTERSTITIAL WATER
Water which can’t be removed during the production of oil and gas from a reservoir.
Types of subsurface water by genesis
1. METEORIC WATERS
Meteoric waters are caused by the infiltration of rainwater and occur near the earth’s surface.
2. CONNATE WATERS
Connate waters are interstitial water existing in the reservoir rock prior to disturbance by drilling and waters which have been buried in a closed hydraulic system and have not formed part of the hydraulic cycle for a long time.
3. JUVENILE WATERS
Juvenile waters are of primary magmatic origin.
4. MIXED WATERS
Mixed waters may be caused by the confluence of juvenile, connate, or meteoric waters.
Subsurface Temperatures
Reference: http://blogs.discovermagazine.com
Subsurface temperature increases from the Earth's surface toward its center.
Bottom hole temperatures can be recorded from wells or other test data.
Geothermal gradients can be calculated from Bottom hole temperatures.
Global average geothermal gradient is 2.6°C/100 m.
Heat flow equals geothermal gradient times thermal conductivity of rock.
Rocks of differing compositions have different thermal conductivities.
Bottom hole temperatures can be recorded from wells or other test data.
Geothermal gradients can be calculated from Bottom hole temperatures.
Global average geothermal gradient is 2.6°C/100 m.
Heat flow equals geothermal gradient times thermal conductivity of rock.
Rocks of differing compositions have different thermal conductivities.
Subsurface Pressures
Subsurface pressures can be calculated by many methods
1. Measured from SEISMIC DATA
Reference: www.sub-surfrocks.co.uk
2. Measured from DRILL STEM TESTS or REPEAT FORMATION TESTS
3. DETECTED WHILE DRILLING A WELL by one of the following
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1) Rapid increase in the rate of penetration.
2) Rapid increase in temperature of the drilling mud. 3) Decrease in density of shale cuttings. |
Subsurface pressures can be classifies as
1. LITHOSTATIC PRESSURE
Caused by the pressure of the rock and transmitted through the subsurface by grain-to-grain contacts.
2. FLUID PRESSURE
Caused by the fluids within the pore space.
Subsurface Fluid Dynamics
Pressure and temperature affect petroleum fluids in the subsurface.
A pure fluid may exist in liquid or gaseous state.
Pressure–temperature phase diagrams can be constructed for petroleum mixtures.
A pure fluid may exist in liquid or gaseous state.
Pressure–temperature phase diagrams can be constructed for petroleum mixtures.
EXAMPLE OF PHASE DIAGRAMS
Reference: https://s3.amazonaws.com
VOLATILE OIL PHASE DIAGRAM
WET GAS PHASE DIAGRAM
PRIMARY MIGRATION
Occurred from movement of hydrocarbons from the source rock into permeable carrier beds.
SECONDARY MIGRATION
Occurred from the movement of hydrocarbons from the carrier beds to the reservoir trap.
Dynamics of fluid flow in basins evolves with time from youth to senility (mature basins).
In young basins, hydrocarbons and connate water migrate from the basin center toward the shallow margins of the basin.
In senile basins, possible slow deep connate convection cells may be present.
In young basins, hydrocarbons and connate water migrate from the basin center toward the shallow margins of the basin.
In senile basins, possible slow deep connate convection cells may be present.
