Facies Architecture Analysis and Modelling of the Sandy Slope Channel Fills at San Clemente, California

Abstract

Sandy slope channel fills can form important hydrocarbon reservoirs, but significant uncertainties exist concerning reservoir architecture. The outcrop of the Miocene-Pliocene Capistrano Formation at San Clemente exposes a ca. 800 m long, 15 m-thick succession of sand dominated slope channel fills. This provides a good case study for us to reconstruct and model facies and associated reservoir architecture based on paleocurrent data, sedimentary logs and large-scale photomosaics collected in the field. The succession at San Clemente represents an oblique section through a large slope channel system composed of 10 channel fills. The laterally relatively continuous exposure reveals channel axis (thick bedded coarse sand and/or gravels), off-axis (thick/medium bedded coarse sand alternating with thin bedded turbidites) and channel margin (thin bedded turbidites and/or siltstone drapes) sub-environments from different channels. Because these sub-environments represent deeper, intermediate and shallower parts of these channels respectively, channel lateral and vertical migration history and resultant overall architecture can be reconstructed using exposed sub-environments within each channel based on the assumption that the 10 channels are similar in their dimensions and facies distribution from channel axis to channel margin. It is believed that the outcrop observed at San Clemente is a result of channel lateral migration and vertical aggradation and degradation rather than just lateral migration or vertical aggradation, and is partly comparable to the modern Lucia Chica channel system, offshore California. Building on this conceptual model, the probabilities of different facies transitions can be modelled and then used to predict the facies architecture at bed, bedset and channel scale. The results show that we can reasonably reproduce the facies architecture observed in outcrop with vertical conditioning data (sedimentary logs or well logs calibrated to core). The transition statistics and conceptual model used in this study can therefore be used as constraints for facies and reservoir architecture modelling in comparable slope channel systems in the subsurface.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015