The Use of Detailed Reservoir Modelling in the Development of a Low Permeability Aeolian Reservoir: Hyde Field, Southern North Sea

M. L. Sweet, A. M. Carter, C. J. Blewden

Hyde Field is a 150 BCF gas field in the UK Southern North Sea. The reservoir, the Permian Rotliegendes Group, contains aeolian, fluvial and sabkha facies. The aeolian facies constitute the dominant flow units. Illite cementation results in low reservoir quality, in the aeolian facies permeability averages 2.5 mD and rarely exceeds 10 mD. To maximize recovery from this field, with its thin gas column and low reservoir quality, Hyde has been developed with 2 long-reach horizontal wells.

A reservoir model that could accurately predict future production had to include large and small-scale heterogeneities. At the scale of individual sets of aeolian cross-strata, it was found that permeability of the coarser grained toes of sets was significantly higher than in the finer grained tops of sets. To simulate flow through cross bedding a model of individual trough sets was constructed and populated with permeability values typical of those seen in core. On a larger scale, models of the spatial distribution of aeolian, fluvial and sabkha facies over the entire field were created using geostatistical indicator simulation techniques. These models were conditioned by data from 8 wells. By careful definition of the model's layering scheme, strongly deterministic elements were inc rporated where facies trends were influenced by laterally extensive stratigraphic surfaces. Average permeability values were assigned to the poorest quality fluvial and muddy sabkha facies. Permeability values for the aeolian and sandy sabkha facies were determined by upscaling models of their internal permeability structure. The resulting distribution of permeabilities across the field, present in a multi-million cell model, was upscaled into a coarser grid suitable for ECLIPSE simulation of the full field.

This new model produced a significantly better match to production data than did our earlier simple layer ECLIPSE model. Our results suggest that in low permeability reservoirs heterogeneity on the bedform scale can have a big impact on well performance.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995