In order to adress the question of oil-induced microfracturing, we pro
pose under specific assumptions (plane circular kerogen flake surround
ed by an homogeneous microfractured porous medium) an analytical metho
d for the determination of the oil pressure increase. It is based on a
mechanical modelling of the kerogen-oil-rock interaction at the ''mic
roscopic'' scale of a kerogen particle. It is shown that the oil press
ure tends towards an asymptotic value when the chemical transformation
of kerogen is completed. The effect of the macroscopic stress variati
on during oil formation process proves to be negligible. However, this
effect must be taken into account for describing the evolution of oil
pressure at earlier stages of oil formation process. The increase in
burial depth induces an increase of oil pressure as well as a variatio
n of the macroscopic stress which both determine the microscopic stres
s field. The possibility of microfracturing depends on the position of
the microscopic stress state with respect to the fracture criterion.
If the duration of the oil formation process is short enough, so that
the macroscopic stress change associated with the corresponding (small
) burial depth increase can be neglected, it is found that microfractu
ring is likely for the usual values of rock tensile strength. However,
in the general case, neglecting the macroscopic stress change can sig
nificantly overestimate the possibility of fracture initiation due to
oil-pressure increase. Considering now the ''macroscopic'' scale of th
e source bed, the evolution equation of the oil pressure are derived w
ithin the framework of Blot's poroelasticity theory. The oil pressure
rate proves to be the sum of a diffusion term which accounts for oil m
igration within the source bed, and of two source terms respectively a
ssociated with the volume expansion tendency of the kerogen --> oil tr
ansformation and the overburden pressure increase.