Page 75 - Petrophysics

MIGRATION AND ACCUMULATION OF PETROLEUM 49

BO
-

2,000- IO0
-
4,000-
-.
6,000- -
8.000 - I50 -
-
- 10.000- - v
IL
W
4 200 g
= 12.000-
I - a
t W
14,000- TEMPERATURE P
- RANGE FOR
16,000 - OIL a GAS
-
18.000 - GENERATION 250
-
20,000 -
-
22,000 - ,300

D
POROSITY (%)
Figure 2.8. Average relationship between porosity and depth of burial for shales, and
the temperatures and depths for the genesis of oil and gas 1151.

MIGRATION AND ACCUMULATION OF PETROLEUM

The genesis of petroleum occurs in compacted clay and shale beds,
which are essentially impermeable to fluid flow. Therefore, the processes
by which hydrocarbons migrate from the source rock to a porous,
permeable reservoir (called primary migration) are not completely
understood. Numerous theories have been advanced to explain the
processes. Possibly, several different mechanisms may be operative
under different environmental and geological conditions. Some of
these are:

a. Transport in colloidal solutions as micelles.
b. Transport as a continuous hydrocarbon phase.
c. Buoyant movement of individual droplets.
d. Solution of hydrocarbons in water moving out of the source rock.
e. Transport by mechanical forces during clay diagenesis.
f. Movement through microfractures in the source rock.