Sand-rich fairways in deep-water clastic reservoirs: Genetic units, capturing uncertainty, and, a new approach to reservoir modeling

Correlation in sand-rich deep-water elastic reservoirs using sedimentary ch aracteristics is examined using well-exposed outcrop data. Individual bed t hickness, or the sedimentary characteristics of single beds, and packages o f beds when viewed in one dimension are found to give an inadequate basis f or interwell correlation over distances greater than 100 m. Offset stacking of beds is the main control over bed thickness variations with scouring pl aying a minor role. Composite units are identified that can be traced over kilometer-scale distances. These units are potentially identifiable on seis mic data and are valuable for interwell-scale reservoir modeling. Pinch-out of sand units is characterized in two end-member styles, onlap and infill. Onlap and infill indicate the influence of paleotopography on deposition, reflecting deposition onto low and high relief, respectively. Onlap is char acterized by gradual deterioration of reservoir quality toward the pinch-ou t, whereas infill maintains good reservoir quality without significant dete rioration close to the pinch-out. Prediction of the proximity of 1-D (one-d imensional) sections to termination of reservoir units at a pinch-out is pr oblematic for both styles. Although 1-D sections provide invaluable data fo r reservoir characterization prediction of 3-D (three-dimensional) sand bod y geometry from bore-hole sections is problematic. Commonly cited channeliz ed and lobate sandstone body geometry does not have diagnostic sedimentary features and recognition of alternative sand body geometry is needed. The d ifficulty in selecting key small-scale sedimentary features that, in turn, are diagnostic of larger scale geometric features limits their value in the up-scaling of reservoir characteristics. A new approach to reservoir model ing of sand-rich deep-water elastic reservoirs is proposed that involves do wn-scaling from mapping of seismically detectable, interwell-scale packages of beds and die paleotopography on which they lie. Once these features are constrained smaller scale characteristics are modeled.