Shell plc confirmed gas in its 48/8b-3Z discovery well at the Selene prospect in the UK Southern North Sea, said license partner Deltic Energy PLC (25%) in an Oct. 31 release.
The well, in the P2437 license area, was spudded on July 30 and reached its total depth of 3,540 m TVDSS on Oct. 17 (OGJ Online, Oct. 21, 2024). The well proved a 160-m thick section of Leman Sandstone which had elevated mud gas readings, confirming the presence of gas throughout the reservoir interval and into the underlying Carboniferous basement.
Subsequent wireline logging and fluid sampling confirmed a live gas column above a gas-water contact at about 3,370 m, which is in the middle of the B-Sand, the key producing interval within the overall Leman Sandstone section. Updated post-well structural maps of the Selene prospect point towards a maximum gas column of about 100 m. Initial indications suggest high-quality dry gas, typical of production from adjacent fields, with no reported H2S.
Based on preliminary information available from the wellsite, an updated Deltic Energy volumetric model estimates that Selene contains gross P50 estimated ultimate recoverable resources of 131 bcf (P90-P10 of 95-176 bcf) which is at the lower end of pre-drill estimates.
The bulk of the recoverable resources are concentrated in the higher quality B-Sand up-dip from the 48/8b-3Z well location, and these should support a simpler and cheaper development option with greater gas production per well than was envisaged pre-discovery, Deltic said.
The combination of a deeper structural crest and a shallower gas water contact has resulted in reduced gas column heights across the structure. The base of the B-Sand and most of the underlying C-Sand are believed to be in the water leg across the south-eastern part of the structure, with the deeper gas readings from the well now interpreted as residual gas rather than a live gas column.
The well confirmed that the B-Sand reservoir properties at the well location were towards the high end of the ranges predicted pre-drill. The B-Sand encountered in the well was 53 m thick (pre-drill P50 of 47 m) with an average porosity of 12.1% (up from 11% P50 pre-drill) and a gas saturation in-line with pre-drill expectations.
These improved reservoir characteristics are supported by a downhole test, which recovered gas samples and indicated 1-5 md permeability above the gas-water contact. These porosity and permeability attributes support the use of more favorable recovery factors for the B-Sand in the updated volumetric model.
As previously indicated, the well was not designed to accommodate a conventional surface flow test, and all the reservoir data required to support a potential future development plan and investment decision has been successfully acquired through this well.
Following demobilization of the rig, which is expected towards the end of next week, there will be a period of detailed analysis of wireline data, core samples, fluid samples, and pressure testing data which will further refine the geological model, volumetric estimates and the proposed development plan.
