Abstract: On the Use of Multilayer Secondary Migration Modelling to Elucidate Complex Filling Patterns in Stacked Reservoirs.
SYLTA, OYVIND, IKU Petroleum Research
Abstract
The distribution of trapped hydrocarbons sometimes show strange
patterns that are not easily explained by the existing knowledge of
source and migration. These patterns may include gas trapped below
under-saturated oil, with a thin seal in-between, and dry reservoir
units in-between hydrocarbon filled units. For the first case it is
often tempting to propose e.g. a new (deeper) source for the deeper
gas simply because it is the most natural explanation. Such a
solution
to the hydrocarbon trapping distribution may, however,
lead to new exploration plays in mature areas, and significant
amounts of capital may be spent investigating the “new
play” with sourcing from an e.g. older, more mature, source
rock.
Before a decision to interpret the complex vertical
trapping in
such a manner is made, an alternative is to investigate whether the
trapping pattern may be explained by a complex migration route
through e.g. a series of fault compartments. Here we discuss how
such an analysis sometimes can explain migration from a source rock
above the carrier and reservoir rock, through a series of fault
blocks, into older flow units. Gas will ususally be generated
further away from the trap (deeper in the basin) than the oil, and
this may result in cross-fault migration into older flow units for
the gas. Using numerical experiments, we can study the criteria for
fault throw distribution, carrier and seal thickness etc. needed
for migrating gas below oil into traps.
The problem described here is a 3 dimensional hydrocarbon flow
problem, and a solution
requires a complex geological description.
We use a multi-layer ray-tracing technique to trace the
hydrocarbons from source to trap through complex migration
pathways. The secondary migration process is suitable for parallel
processing, with each flow unit represented by one process in the
computer(s). Thus we can quickly assess whether a geological
scenario is likely to or not likely to cause trapping of e.g. gas
below oil.
AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah