Quantifying the Spatial Geometry and Interior Complexity of Paleocave Carbonate Reservoirs in the Tarim Basin, China
Collapsed paleocave reservoirs, developed in Lower and
Middle Ordovician limestone in the Tarim oil field, China, are products of near
surface karst processes and diagenesis. Integration of geometric attributes
with seismic reflection
facies can construct three-dimensional architecture of
the paleocave systems which consist of collapsed paleocave brecciated bodies
and seismic chaotic
reflection
facies. The former are characterized by seismic
amplitude bright strings, which can be identified and located with amplitude
gradient attribute. The latter describe chaotic
reflection
patterns and are
defined on the basis of degree of brecciation. Brecciated bodies are encircled
by the paleocave facies. The three-dimensional architecture of the paleocave
systems defines the major trends of paleocave systems, which are attributed to
solution enhancement (cave development) of northeast- and northwest-trending
joint systems. The collapse-related faults are circular or cylindrical. Most
are normal faults and have
small
displacement. The vertical heterogeneities of paleocave reservoirs are quantified by the integration of logging data and
production data. Log electrofacies analysis and calibration with core data and
borehole imaging logs lead to the definition of reservoir rock types at wells.
These rock types define porosity types which are associated with reservoir
quality. The quantified vertical permeability barriers are characterized with
high resistivity and separate reservoirs into different flow units. Constrained
with three-dimensional architecture of the paleocave systems, seismic impedance
attribute and rock type logs, paleocave reservoir rock type and porosity models
are simulated. The spatial geometry and interior complexity are assessed by
integrating these models with reservoir production data. Our results show that
reservoir architecture combined with reservoir property models can have
important implications for hydrocarbon prospectivity and reservoir development.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California