3-D Static and Dynamic Modeling of a Carbonate Reservoir: The Lower Cretaceous La Tosca Unit (Huitrín Formation, Neuquén Basin, Argentina)

The Lower Cretaceous Huitrín formation of the Neuquén Basin (Argentina) consists of mixed clastic-carbonate-evaporite sediments of shallow marine to continental settings. The unit is subdivided into three lithostratigraphic members Chorreado, Troncoso and La Tosca, all of which are hydrocarbon bearing in varying locations of the basin. This work presents the integrated 3D static and dynamic reservoir characterization and modeling of La Tosca unit. The main structure in the area is an East-verging basement anticline with ElPichanal, PataMora and PuestoMolina fields all being located on its western flank. Both a High Resolution Sequence Stratigraphic model and a Discrete Fracture Network model, were built through the integration of seismic, core, well cuttings, borehole imaging and log data, and validated by well tests and dynamic simulations. La Tosca depositional sequence consists of a third order transgressive-regressive 30m-thick cycle accumulated on a shallow carbonate platform. Main deposits comprise low- to high-energy subtidal to intertidal facies including skeletal banks, ooid-skeletal shoals, peloidal platform interior, algal mats and sabkha deposits. The facies stacking pattern allows further subdivision of the unit into possible fourth and fifth order accommodation cycles. Fourth order cycles show evident facies partitioning, with overall argillaceous-carbonates dominating transgressive hemicycles and clean carbonates (ranging from skeletal and oolitic grainstones to algal-mat boundstones) dominating regressive hemicycles. Fifth order cycles also show similar facies partitioning, with transgressive hemicycles bearing argillaceous limestones and regressive cycles characterized by oomoldic and skeletal grainstones. Two types of fractures,diagenetic and tectonic, were identified, with diagenetic fractures showing preferential occurrence within the regressive portions of the 5th order cycles mainly in oomoldic grainstones due to enhanced cementation and in algal mats due to desiccation. Tectonic fractures are ubiquitous and their intensity is related to fault distance. We propose a model of dual porosity where matrix acts as hydrocarbon storage and fractures provide production mechanism. The best matrix reservoir intervals occur within 5th order regressive hemicycles where permeability of oomoldic and algal mat facies is enhanced by a network of centimeter-scale diagenetic fractures.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California