3.3 North Sydney F-24

The Shell-Murphy et al. North Sydney F-24 well (1976) was the second of two wells drilled in the offshore Sydney Basin. The operators’ rationale for drilling the well was to “test the deliverability of the sandstones encountered in the first [P-05] well.” (Shell, 1976). The sandstones encountered in P-05 had generally fair to good porosities and were gas-charged but generally have low to modest permeabilities. None of these zones were flow tested, thus their deliverability potential was unknown. Nevertheless, a significant number of mud-gas shows were present over a 750 m thick interval, with defined log pay mostly within the South Bar Formation (and the remainder in the Sydney Mines Formation) .

Prior to drilling there were rumors the Hudson’s Bay Oil & Gas East Point E-49 well in the Magdalen Basin to the west tested significant gas. This well was drilled in mid-1970 and re-entered in early 1974 to test three previously encountered gas-bearing fluvial sandstones. The rumor was subsequently confirmed with E-49 flowing 5.3 MMcf/d gas but from a younger (latest Stephanian) sandstone (COGLA, 1990). Another driver to test the P-05 sandstones was the large areal extent of the structure’s closure, then-estimated to be about 187 km².  However, beyond the original seismic programs (Murphy 1971a, b), no additional data to refine the structural interpretation was collected.

The F-24 well was located 5.6 km west-southwest of P-05 on the crest of the structure and drilled in 60.3 m water.  The stratigraphic succession penetrated was near identical to that of the P-05 well though with modest variations in formation thicknesses. Its formation tops and related information are shown graphically in Figure 3.1 and tabulated in Table A. The ages defined in the well’s later biostratigraphic analysis (Dolby and LaBorde, 1976) reasonably equated with the later revision of P-05’s ages by Williams et al. (1990). It was most recently re-assessed by Weston et al. (2017).

Numerous mud-gas shows were present throughout the Mabou and Morien group sediments in concentrations similar to those in the P-05 well. The gas was overwhelmingly methane and the shows increased with depth.  New log analysis reconfirms most shows are related to coals and coaly intervals and sandstone reservoirs have modest porosity. Four conventional cores were recovered from reservoir sands within the Waddens Cove (cores 1 and 2) and South Bar (cores 3 & 4; channel sandstones) formations that confirmed the expected reservoir characteristics (Table B). As detailed in Table C, the two intervals selected for testing had no flow to surface, even following acidizing and fracturing.  It should be noted, that the intervals selected for testing had limited net pay. Had some of the other more porous intervals been tested the test results may have been more favourable. After the testing concluded, the well was plugged and abandoned.