Possible Modes of Primary Migration

Ø  Continuous Oil Phase

Ø  Colloidal or Micellar Solution

Ø  Droplet/Bubbles

Ø  Molecular Solution

Ø  Microfractures

1.Continuous Oil Phase

Movement of petroleum is in continuous oil phase during primary migration.

Oil saturated in pore spaces in mature source rock upto 50%, in terms of pore-fluids and assumed that rest of the pore spaces are covered with structured water

If some of the interior surfaces are oil-wet rather than water wet then oil will move as continuous phase.

Deeply buried source rock, at maximum phase of oil formation, with high degree of compaction offer greater opportunity to primary migration as continuous oil phase

Driving force under such condition could be pressure gradient.

2.Colloidal and Micellar Solution

Colloid: size range; 1-10,00 nm (10-10,000 Ao)

Micelle: an aggregate of surfactant (which lower the surface tension) molecules dispersed in a liquid colloid, may be hydrophilic or hydrophobic.

The transport of petroleum compounds through pores in source rocks as colloidal and micellar solution is proposed by Baker and Meinschain (1959).

Organic compound (colloidal compounds) act as polar organic compound, with hydrophilic part outside and hydrophobic part inside the molecule as micelle.

It has been reported that sediments and crude oil act as polar surface (Lousi, 1967; Seifer and Howells, 1969 and Seifer, 1975)

This might be the only way to solubilize practically water-insoluble petroleum hydrocarbons in aqueous solution in relatively low temperature.

All in all, solubilization of H/Cs and its transportation thorough micellar solution does not seam to be likely process.

if micellar process were responsible for petroleum migration oil should also be enriched in N-S-O polar compounds, which more likely to form micellar solution, but crude oil are depleted in these polar compounds, only certain shallow oil are rich in such compounds.

3.Droplet/Bubbles

Transportation of oil and gas in form of individual droplet/bubbles through narrow, water saturated pores by phenomenon of Capillary pressure.

If droplet; small or same size with pore spaces there will be no restriction for movement of petroleum.

If droplet; larger than pore spaces, the capillary pressure will overcome and oil will move in form of bubbles.

> Capillary pressure is higher for small pore spaces.

4.Molecular Solution

Another way of transporting mechanism, during primary migration.

There is solubility of different petroleum compounds within the water.

In general; low molecular weight H/Cs are more soluble in water than high molecular weight H/Cs, e.g., benzene and toluene are among most soluble common petroleum hydrocarbons.

Solubility of oil range from 10ppm below 100 oC and 100ppm below 100-200 oC.

Solubility increases; with increasing in temperature

Solubility decreases; with increasing C number.

With increase in P there should be increase in Solubility among lighter H/Cs, when subsequently pressure decreases the H/Cs released from the solution (within reservoir).

5.Microfractures

When pressure increase on source rock, decreases the porosity, thus creates minute fractures, cracks or fissure within source rocks (This will allow petroleum to migrate).

Tissot (1971), Snarsky (1962), and pelet (1971) pointed out that rock fractures in dense, deeply buried shale; either by over pressure of enclosed fluids or due to creation small pockets of over pressure gas formed during petroleum generation.

Snarsky (1962), pointed, if mechanical strength of rock exceeds, fracture will occur in rocks (this is subsequent release in pressure), which promote migration.