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