3.3 North Sydney F-24

Figures

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.

STRATIGRAPHY

DEPTH (MD)

THICKNESS

Group

Formation

Approx.Seismic Marker

Metres

Feet

Metres

Feet

Top

Base

Top

Base

KB

n/a

 

29.9

-

98

-

-

-

WD

n/a

 

62.8

-

206

-

-

-

Casing Shoe

n/a

 

289.5

-

950

-

-

-

Pictou

 

P300

289.5

521.8

950

1712

232.0+

762+

 

Undivided

 

289.8

521.8

950

1712

232.0+

762+

Morien

 

 

521.8

1436.1

1712

4712

914.3

3000

 

Sydney Mines

C303

521.8

946.4

1712

3105

424.6

1393

 

Waddens Cove

 

946.4

1085.0

3105

3560

138.6

455

Westphalian C/B Unconformity

 

NP

NP

 

 

 

South Bar

C308

1085.0

1436.1

3560

4712

351.1

1152

Westphalian B/A Unconformity

 

NP

NP

 

 

Riversdale

 

 

NP

 

NP

 

 

 

Westphalian-Namurian Unconformity

 

1436.1

4712

 

 

Mabou

 

 

1436.1

1600.1

4712

5250

164.0

538

 

Point Edward

 

1436.1

1487.4

4712

4880

51.3

168

Intra-Namurian A Unconformity

 

NDE

NDE

 

 

 

Cape Dauphin

 

NDE

 

NDE

 

 

 

Table A. Formation tops for the Shell et al. North Sydney F-24 well based on lithostratigraphy as defined by Boehner and Giles (2008), Canstrat lithology log (1976), F-24 well history report (Shell, 1976), and biostratigraphic analyses from Dolby and LaBorde (1976), Williams et al. (1990), and Weston et al., 2017b.

 

 

Core No.

Unit

Interval

m (ft)

Recovery

m (ft)

Lithologies

Comments

1

Sydney Mines Fm. (Morien Gp.)

954.0-962.8 (3130-3159)

8.8 (29)

97%

Shale (67%): medium grey, calcareous to non-calcareous, silty, occ. coal fragments. Sandstone (30%): lt. grey, fine-med. grain, occ. silty, abdt. coal fragments, micaceous. Siltstone (3%): lt. grey, v. micaceous, argillaceous, shale interbeds

Sandstones have poor to fair (5-10%) to occ. good (15%) porosity, no fluorescence, good light yellow cuts, gassy.

2

Sydney Mines Fm. (Morien Gp.)

963.1-972.1 (3160-3189.4)

9.0 (29.4)

98%

Sandstone (70%): very fine to fine grain, occ. med.-coarse, sub-ang. to sub-rd., micaceous, carbonaceous, argillaceous, occ. coaly. Shale (18%): grey, silty, coaly, micaceous. Siltstone (4%): lt. grey, sandy, micaceous, carbonaceous. Coal (7%): black, bituminous, tr. shale.

Sandstones variably poor to fair porosity (5-10%), occ. fluorescence, weak to good light yellow cuts, gassy odour

3

South Bar Fm.

(Morien Gp.)

1100.2-1118.9 (3610-3671.2)

18.7 (61.2)

100%

Sandstone (100%): fine-medium grain, well sorted, var. calcareous and argillaceous, var. carbonaceous and coaly, tr. pyrite, var. micaceous, rare bituminous material.

Porosities: Range from 5-10%, rarely 10-20%. Shows: thin, minor yellow to blue cut, fluorescence.

Gas: Tr. 0.13-0.51%, peak 1.12-1.48%.

4

South Bar Fm. (Morien Gp.)

1356.0-1370.5 (4449-4496.7)

14.3 (46.8)

97%

Conglomerate (10%): fine grain, quartzose, pyritic, calcareous,

Sandstone (90%): fine-coarse grain, var. sorted, var. calcareous and argillaceous, tr.-common. pyrite, tr. carbonaceous, var. micaceous

Porosities: Range from 0-10%, rarely 10-20%. Shows: thin, minor yellow to blue cut, fluorescence.

Gas: Tr. to 0.15-0.55%.

Table B. Conventional cores recovered from the Shell et al. North Sydney F-24 well (Shell, 1976).

 

 

DST No.

Unit

Lithology

Test Interval

m (ft)

Perf Intervals

m (ft)

Recovery

Comments

1

Point Edward Fm. (Mabou Gp.)

Porous (?%), fine grain, siliceous sandstone

1511.7-1519.0 (4960-4984)

1511.7-1519.0 (4960-4984)

None

No gas flow after perforation. Zone acidized. No flow.

2

South Bar Fm. (Morien Gp.)

Porous (?%), medium grain, siliceous sandstone

1242.0-1306.0 (4075-4285)

1242.0-1251.8 1263.3-1275.5 1292.3-1304.5 (4077-4107)

(4145-4185) (4240-4280)

None

No gas flow after perforation. Zone acidized and sand fracked. No flow.

Table C. Formation tests in the Shell et al. North Sydney F-24 well (Shell, 1976).

 

 

Figures