Linda M. Bonnell,1 I. Toenne,2 Robert H. Lander,1 and R. E. Larese3
Petrofacies are classifications of sandstones based on textural and compositional characteristics that lead to similar petrophysical properties for a given burial history. Petrofacies may or may not be directly linked to lithofacies types and are useful for reservoir quality prediction and comparison. In this study we used the petrofacies concept together with a sequence stratigraphic framework and gross depositional environments (GDE) to predict the reservoir quality in four Jurassic reservoir units in Blocks 6406/5, 6 and 9 on the Norwegian continental shelf using the approach described by Lander & Walderhaug, 1999. Reservoir quality predictions for 7 pseudo-well locations were based on calibration of the model parameters to analog samples from 12 nearby wells that span a wide range of GDEs, reservoir depth, quality and fluid pressure conditions.
The results of 1000 Monte Carlo realizations for petrofacies types at the 7 pseudo-well locations suggest that grain-coat coverage and grain-size exert the most influence over reservoir quality variations in the area. We have defined means of 7% intergranular porosity and 1mD permeability as benchmark values for evaluating whether a petrofacies type will be a good gas/condensate reservoir. Although, there is some variability between the pseudo-wells, we can generalize that only medium and coarse-grained sandstones with high grain-coat coverage will have reservoir quality above the benchmark means for reservoirs in the prospect region at burial depths greater than 4300 meters. These types of sandstones are associated with wave-dominated shoreface, tidally-influenced lower coastal plain and incised valley fill deposits in the study region.
1Geocosm, Austin, Texas; e-mail: firstname.lastname@example.org, email@example.com; Visiting Scientists, Bureau of Economic Geology, The University of Texas at Austin, University Station Box X, Austin, Texas 78713.
2Phillips Petroleum Company Norway, P.O. Box 220, Tananger, 4056, Norway.
3Fluid Inclusion Technologies, 2217 N. Yellowood Ave, Broken Arrow, OK 74012.