Abstract A significant contribution to the natural gas production is delivered from massive reservoirs with bottom water of several unique fields of Western Siberia, confined to highly productive Cenomanian formation. Most of them are brownfields at low reservoir pressures.
Despite the high permeability of the reservoirs, a strong heterogeneity in the distribution of reservoir pressure and elevation of the gas-water contact (GWC) is observed, which is not reproduced by full-scale flow simulation models.
The purpose of this study was a comprehensive analysis of permeability data from various sources for one of such objects to explain the observed features of field development. The analysis of areal and vertical permeability distribution includes the results of well log interpretation (WLIR) by three methods in 81 wells over more than 250 m of reservoir thickness, and several tens of pressure build-up curves (PBU). The analysis made it possible to identify the main causes of the uneven distribution of pressure, GWC elevation, drainage of gas volumes associated with a multi-fold difference in the average permeability between the drilled central (dome) part of the site and on its periphery.
As the gas is produced and the GWC shifts upward, the contrast in permeability of the drilled and un-drilled zones increases, and the most permeable intervals pass to the area below the GWC. It is for the first time for the long-developed highly productive gas reservoirs with bottom water in the Cenomanian formation that complex analysis of well logging data, field development control data, and 3D reservoir models has been used to justify interrelation between the inhomogeneity of gas drainage, reservoir pressure distribution and GWC advance and the distribution of permeability within the reservoir. The need for detailed geological analysis is shown for constructing a model of the reservoir properties distribution in the inter-well space to help localizing and activating the remaining gas volumes, which are greater than 440 billion m for the Medvezhye field alone.