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Integration between Mechanical Stratigraphy & High Resolution Sequence Stratigraphy; The story Continues Layaan Al Kharusi Dr. Gregor Eberli, Dr. Gene Rankey Comparative Sedimentology Laboratory, RSMAS University of Miami Introduction • Reservoirs are complex and influenced by many factors. • Better understanding of lateral heterogeneities in the reservoir and prediction of flow units and an insight into fracture pattern is the key to more successful reservoir development. • Hence – The aim of this project is to characterize fracture distribution, connectivity and intensity. Goals of Study To identify a relationship between mechanical stratigraphy and high resolution sequence stratigraphy To predict fracture patterns from stratigraphic information SEQUENCE STRATIGRAPHY Genetic Units Onset of flooding Regressive Hemicycle Transgressive Hemicycle Decreasing Accommodation Space Increasing Accommodation Space Onset of flooding The stratigraphic record of one cycle of creation of accommodation space. MECHANICAL STRATIGRAPHY Mechanical Stratigraphy The partitioning of different rock layers based on their mechanical behavior • A Mechanical Unit is defined by a unique combination of type, density or orientation of fractures distinct from over and underlying units. It can be composed of one or more lithologic beds. • A surface where a statistically significant number of fractures terminate is identified as a Mechanical Boundary. Variables 1 • • • • Bed Thickness Lithology Stress Regime Bed bounding surfaces – Shale partitioning • Internal bed forms • Diagenesis • Porosity Why are we concerned with sequence stratigraphy when looking at Mechanical Stratigraphy? • Sequence stratigraphy determines facies and their distribution (lithology control) • Sequence stratigraphy determines diagenesis (cement control) • Facies and diagenesis determine type of pores and porosity • Sequence stratigraphy determines bounding surfaces (erosional, mfs…) thus determining bed contacts • Facies, diagenesis and porosity control rock strength and rheology St. Louis, Missouri Lower Carboniferous (Visean) Carbonates Two types of heterogeneity Bed-scale lateral heterogeneity (e.g. mud lens, pinch out, thickening or thinning of beds, channels) Intrabed-scale heterogeneity; bed forms, cross bedding, complex compartmentalization of individual units SEQ STRAT LITHOLOGY MECHANICAL UNITS FRACTURE DENSITY PLOT (No. of Fract./m) M.U.9 1.1 15m M.U.8 3.4 M.U.7 M.U.6 M.U.5 1.3 M.U.4 M.U.3 M.U.2 M.U.1 M P G 1.9 1.5 Gravois Section Gravois Section M.U.10 SEQ STRAT LITHOLOGY MECHANICAL UNITS FRACTURE DENSITY PLOT (No. of Fract./m) 2.8 M.U.15 M.U.14 2.4 M.U.12 M.U.11 18m M.U.10 M.U.9 M.U.8 1.8 M.U.7 M.U.6 M.U.5 M.U.4 M.U.2 M.U.1 M W 0.7 1.1 1.4 M.U.10 FRACTURE DENSITY PLOT (No. of Fract./m) 1.3 M.U.9 M.U.8 M.U.7 20m Cardinal Quarry Section SEQ STRAT LITHOLOGY MECHANICAL UNITS 1.3 1.3 3.27 M.U.6 M.U.5 M.U.4 1.27 M.U.3 M.U.2 M.U.1 2.4 3.27 Highly Fractured Grainstones When thin bedded • Complex compartmentalization and heterogeneity • Continued Stress producing fracture infilling 0.5m Sheep Mountain Anticline, Wyoming Mississippian Carbonates Sequence Hierarchy (from 5th order bed scales to 3rd composite beds) 0.5m 5th Order Transgressive and Regressive Hemicycles 0.5m Fracture Hierarchy in Sheep Mountain Anticline 10m Graph of Fracture Density versus Bed Thickness & Lithology in Sheep Mountain Anticline Bed Thickness vs. Fracture Density Packstones to Wackestones 400 Bed Thickness (cm) 350 300 Grainstones 250 200 Mudstones 150 100 50 0 0 5 10 15 20 Fracture Density (No. of fractures per 100cm) 25 30 35 In Summary • These results show that fracture distribution within mechanical units are predictable within a framework of sequence stratigraphy, depositional and diagenetic history. • Fractures are influenced by variability at scales from bed form to composite sequences. Future Directions • Predictive modeling of mechanical units and boundaries with their fracture patterns is the next wave of this study.