MORETTI, ISABELLE
Institut
Francais du Petrole, Rueil Malmaison, France
Abstract: Abnormal Pressures And
Fluid Migration
In Foreland
Thrust emplacement induces the fast arrival
of consolidated rocks at the top of foredeep deposits which may be very
recent and still poorly compacted. Often, the thrust sheet consists of
deep pre-compressional series which have already a low porosity due to
formal burial compaction. In addition, the decollement level usually has
a very low transverse permeability. The pressure field in the forelan is
thus strongly influenced by the thrusting since the formation water can
not escape vertically. Using numerical modeling we quantify the variation
in the pressure field induced by the thrusting, and the resulting hydrocarbon
migration
pathways in the foreland.
A large number of forelands are continental, as
all the American ones from the Andes to the Rocky mountains. In addition
when some parts remain marine as in the Apennines, the internal part emerges
and then is affected by infiltration of meteoric water. To take into account
the variations induced by this water circulation, the potential hydrodynamism
has been computed and the resulting abnormal pressure compared to well
data in the Andean foreland. Competition between downward migration
of
the water and upward
migration
of the HC induces potential hydrodynamic
traps. The resulting water pathway is compared to the one deduced from
chemical and isotopes studies of samples of springs leaking near the thrusts
in the Bolivian Sub Andean Zone.
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas