Open Ground - The Clarence-Moreton Gas Story

The NSW portion of the Clarence-Moreton Basin — the Casino Trough and its flanking structures at Hogarth, Clifden and Grafton — is one of the very few onshore basins in eastern Australia where gas has flowed to surface from multiple wells, on multiple structures, across multiple stratigraphic levels, and where the ground today sits open. This is not frontier acreage resting on a geochemical anomaly. Gas blew out of Grafton No. 1 in the early 1900s. Clifden No. 2 recovered gas at 388,000 cf/d. Hogarth No. 2 tested gas at 500,000 cf/d on drill stem test in 1970 and was completed as a shut-in gas well producing 94% methane — described by the operator as requiring "very little if any treatment... before using as town gas supply." Thirty years later, Cedar Point-1 drilled 300+ metres of near-continuous strong gas shows through an overpressured coal-bearing section in the Casino Trough.

The scale question is answered by the stratigraphy, not by any single well. The basin stacks a conventional sandstone play (the Koukandowie/Marburg "White Sandstone", a stratigraphic equivalent of the Precipice Sandstone — the pay zone of the Moonie and Roma fields), a coal seam gas play (Walloon Coal Measures plus deeper Ipswich, Raceview and Nymboida coals, with seams up to 9 m thick intersected in Kyogle-1), and a largely undrilled Triassic infrabasin interpreted on seismic to reach ~1,300 m thick. The 1981 palynology places the section in the wet gas and condensate window (Ro ≈ 1.2%) — a thermally mature source kitchen, not a marginal one. Around 1,000 km of 1980s seismic exists over the NSW basin.

Why revisit it? Because in roughly a dozen wells over almost seventy years, no operator ever placed a modern, undamaged completion across the proven pay. Every campaign ended for mechanical, financial or political reasons — never because the gas wasn't there. A partner picking this up today inherits a proven petroleum system, a documented flow-rate baseline, an existing seismic library, and no incumbent — at the cost of desktop work and a modern appraisal well, in a state actively short of gas.

Exploration history

• 1898–1902 — NSW Government / private syndicates — Grafton Racecourse. Model: shallow structural gas near Grafton. Grafton No. 1 drilled to 3,698 ft; gas blew out at an unrecorded rate from ~3,100 ft (a sandstone section at 2,945–3,183 ft, later correlated to the Marburg/Koukandowie). Grafton No. 2 followed nearby to 4,582 ft. In 1918, bore water and sediment analysed by the Department of Mines yielded traces of oil "smelling of kerosene." Departure: pre-modern technology — no logging, no testing capability, no gas market. The blowout horizon was never flow-tested.

• 1955 — NSW University of Technology (Prof. D.W. Phillips) — Grafton Racecourse redrill. Model: stratigraphic investigation of the Jurassic section. Cored and described 400–2,600 ft; confirmed carbonaceous, gas-prone Jurassic section; fluorescence tests negative for liquids. Departure: academic program, completed and closed.

• 1958–1962 — Clarence River Basin Oil Exploration Co. N.L., then B.O.C. of Australia — Clifden Dome (five bores). Model: anticlinal gas trap, targeting the Grafton No. 1 gas horizon at a predicted 1,450–1,500 ft. Clifden No. 1 (1958–59, diamond core rig) hit gas at 606 ft and ~880 ft — the ~880 ft zone built 8 psi at surface and the gas caught fire at the wellhead — but was abandoned at 1,290 ft, above target, after the hole caved and deflected. Clifden No. 2 (1961) recovered gas at 388,000 cf/d from 1,943 ft or higher; BMR core analysis showed porosity of 12.3–16.5% but permeability below 0.1 md at the sampled (shallow) levels. Clifden No. 3 (1962) was B.O.C.'s first well in Australia — "It has been quite a shock to us" — plagued by severe deviation through 65° dips on the dome flank; drilled beyond 3,496 ft. Departure: mechanical defeat (caving, deviation, tight shallow cores) and small-company exhaustion; the deeper target sandstone under the dome was never validly tested.

• 1968–1974 — Clarence River Basin Oil / Clarence Oil & Minerals Co. N.L. (Commonwealth-subsidised, PEL 66) — Hogarth Dome (four wells). Model: initially anticlinal closure (350 ft of closure at base Grafton Formation), evolving after Hogarth 2 into a facies-controlled permeability trap in the Precipice-equivalent "White Sandstone." Hogarth 1 (1968, TD 3,995 ft): full Schlumberger log suite indicated hydrocarbons at ~2,125, 2,924–2,928, 3,078–3,090, 3,106–3,113 and 3,515 ft, with core porosity to ~14% and permeability to 24 md — but all four DSTs failed ("packer failed to seat") and the well was abandoned without ever testing the log-indicated zones. Hogarth 2 (1970, TD 3,653 ft): DST 6 over 2,975–3,060 ft flowed gas to surface in 7 minutes at 0.5 MMcf/d; completed as a cased gas well, flowing 246 Mcf/d post-acid and stabilising at ~120 Mcf/d, shut-in pressure building to 1,200 psi; gas analysis 94.1% methane. Reservoir engineering showed k = 4.5 md, kh = 73 md-ft, skin = +18.75, flow efficiency 0.51 — more than 50% formation damage from the drilling and completion itself. Hogarth 3 stepped out ~2,500 ft and found the sandstone tight (abandoned at 3,140 ft), confirming facies control. Hogarth 4 (1973–74) was drilled with a modified Longyear mineral core rig — nine months to reach 3,843 ft — and its results were never properly written up (the Geological Survey logged the core in 1978). Departure: liquidation. The company collapsed with Hogarth 2 shut in behind a padlocked fence; the NSW Government finally plugged the well in 1986 using derelict-lands rehabilitation funds.

• 1980s — Endeavour Resources and others — basin-wide conventional campaign. Model: modern seismic-led structural/stratigraphic exploration. ~1,000 km of seismic acquired; three wells drilled (Kyogle 1, Sextonville 1, Pillar Valley 1); commissioned re-analyses of the Hogarth logs (Crocker, 1981) concluded gas is present above 3,116 ft in Hogarth 1 with average porosity 17.8%, and that the 2,530–2,540 ft zone was likely oil-bearing and "should be tested." Palynology established the wet gas/condensate maturity window. Departure: 1980s oil-price collapse and corporate priorities; the recommended re-tests were never drilled.

• 2001 — Suncor Energy Developments / Earth Resources Australia on Metgasco's PEL 16 — Casino Trough CBM program. Model: coal seam methane in the Walloon and deeper coal measures. Three slimholes: North Casino 1, Cedar Point 1, Casino South 1. Cedar Point-1 (TD 840 m) logged near-continuous mud-gas readings of 50–90% LEL from 515 m to TD, intersected multiple coaly horizons, and returned a permeability test (0.17 md at 679–694 m) that terminated when the packer ruptured in a stressed, overpressured hole — reservoir pressure 6,850 kPa, an artesian head ~14 m above ground. Departure: corporate portfolio retreat, then the NSW CSG policy era — Metgasco's Northern Rivers licences were ultimately bought back by the NSW Government under the 2014–15 NSW Gas Plan (this last point is from public record, not the data package — verify current tenure status before publishing).

Why the grade is still available

The gas is still there because nothing that happened in this basin ever disproved it. Every exit was mechanical, financial or political:

• The tests failed; the rocks didn't. All four Hogarth 1 DSTs failed on packer seat — its best log zones (porosity 13–21%, Sw as low as 33%) were never flowed. Clifden 1 was abandoned 200 ft above its target after hole collapse. Clifden 3 was lost to deviation. Cedar Point-1's only permeability test ended with a ruptured packer.

• The one real completion was crippled and still flowed. Hogarth 2 delivered 0.5 MMcf/d on DST through a packer that wouldn't hold, then stabilised at 120 Mcf/d behind quantified >50% formation damage (skin +18.75). Undamaged, the same reservoir supports a multiple of that rate — and its own operator's engineers said so at the time.

• The play concept was solved and then orphaned. By 1973 the operator understood this is a permeability/facies trap play requiring seismic-led stratigraphic exploration — "further exploration should aim at detecting permeability traps rather than anticlinal structures" — and then went into liquidation before drilling it. The 1980s seismic that could do this was acquired by others and never combined with the Hogarth well control.

• Departures were corporate, not geological: a liquidation (Clarence Oil & Minerals), a contractor's shock first Australian well (B.O.C.), an oil-price collapse (1980s), a portfolio retreat (Suncor), and a government buyback (Metgasco). No operator ever left because a valid test came up dry.

• The modern toolkit has never touched it. No well in the basin has ever been drilled with inhibited mud designed for its kaolinitic sandstones, completed with modern stimulation, or tested with modern downhole equipment. The 1981 log reviewer's caveat still stands: the existing data "correspond to obsolete tools."

"The miss, precisely"

Across nearly seventy years and a dozen wells, no operator ever placed a modern, undamaged completion across proven pay. Hogarth 2 flowed half a million cubic feet a day through a packer that wouldn't seat and stabilised at 120 Mcf/d behind measured 50% formation damage; Hogarth 1's best log zones were never tested because all four packers failed; Clifden 1 was abandoned 200 feet short of its target when the hole caved; Cedar Point-1's only permeability test ended when the packer burst inside 300 metres of continuous gas shows. This basin has never once been asked the commercial question with tools capable of answering it.

The most significant results the system has produced

Well (year)	Result	Why it matters
Grafton No. 1 (1898–1902)	Gas blew out from ~3,100 ft; rate unrecorded	First proof of a charged, pressured system; the blowout horizon (Marburg/Koukandowie equivalent) has never been validly tested
Clifden No. 2 (1961)	Gas recovered at 388,000 cf/d from 1,943 ft or higher	A second structure, 60+ km from Hogarth, flowing gas from the same broad stratigraphic level — this is a system, not a one-off
Hogarth No. 1 (1968)	Log-indicated gas zones 2,924–3,113 ft; φ 13–21%, Sw 33–66%; core perm to 24 md	Quantified porous, gas-saturated reservoir — and none of it was ever flow-tested (all DSTs failed mechanically)
Hogarth No. 2 DST 6 (1970)	Gas to surface in 7 minutes; 0.5 MMcf/d from 2,975–3,060 ft*	The basin's best measured flow — achieved despite packer trouble during the test
Hogarth No. 2 completion (1970)	Stabilised 120 Mcf/d; shut-in pressure to 1,200 psi; 94.1% methane, sales-quality; k 4.5 md, kh 73 md-ft, skin +18.75	A real, produced gas well. The rate was throttled by quantified completion damage (flow efficiency 0.51), not by the reservoir
Hogarth No. 1 zone 2,530–2,540 ft (1981 re-analysis)	φ 21.2%, hydrocarbon saturation 57%, interpreted oil-bearing — "should be tested"	Untested potential oil leg identified by independent review; still untested today
Cedar Point-1 (2001)	Near-continuous mud gas 50–90% LEL from 515 m to TD 840 m; reservoir pressure 6,850 kPa (artesian, +14 m head)	Demonstrates a gas-saturated, overpressured coal-bearing section in the Casino Trough — a second, unconventional play beneath the conventional one
Basin palynology (1981)	Vitrinite reflectance ≈ 1.2%; wet gas/condensate window	Thermal maturity confirmed — the kitchen works

* The source report quotes this interval as both 2,975–3,060 ft and 2,979–3,064 ft in different sections; the flow rate is quoted as both "0.5 MMCFD" and "500,000 CFD" (consistent).

Geological setting

The Clarence-Moreton Basin is a broad Mesozoic intracratonic basin overlying the New England Fold Belt, extending from the Kumbarilla Ridge in Queensland to the east coast. Its NSW depocentre is the Casino Trough, northwest of Casino. The productive section, top down: Grafton Formation (150–250 m, regional seal-prone fluvio-lacustrine unit), Kangaroo Creek Sandstone (200–?500 m quartzose braided-stream sands), Walloon Coal Measures (30–400 m; coal, gas and minor oil; the "Mallanganee Coal Measures" of the old reports), and the Bundamba Group — Koukandowie Formation (?50–400 m; the "Marburg Formation" of the Hogarth wells and host of the gas-bearing White Sandstone, a Precipice Sandstone equivalent) over the Gatton Sandstone (200–600 m of stacked channel sands, largely untested). Beneath lies a Triassic infrabasin — Ipswich Coal Measures, Chillingham Volcanics, Nymboida Coal Measures (interpreted at 500–1,300 m thick on seismic at Pillar Valley) — effectively unexplored. Late Cretaceous compression generated the drilled structures (Hogarth Dome with 350 ft of mapped closure, Clifden Dome, and thrust-related anticlines), while the Hogarth results show charge is ultimately facies-controlled: the exploration problem is finding permeability fairways within a regionally gas-charged section. Source rocks are the coal measures themselves plus Marburg siltstones, sitting in the wet gas/condensate window. The practical drilling hazards are known and mappable: Tertiary dolerite/basalt sills (intersected in Hogarth 1, 2, 4, Clifden 1 and Cedar Point-1), artesian water flows, and high horizontal stresses at depth in the trough.

Top three targets

1. Hogarth Dome re-entry/twin — convert a historic gas well into a modern deliverability test. Twin Hogarth 2 (or drill the updip location its own dipmeter data recommended) with inhibited mud, modern logs and a properly stimulated completion across the 2,960–3,023 ft White Sandstone, plus the untested 2,530–2,540 ft possible oil zone in Hogarth 1. What it achieves: the single cheapest, highest-confidence demonstration in eastern NSW that this basin flows commercial gas — removing the skin-damaged 120 Mcf/d figure as the basin's headline number and anchoring any resource booking. All the well control, log re-analyses and reservoir engineering to design this well already exist.

2. Casino Trough coal/tight-gas fairway — quantify what Cedar Point-1 only glimpsed. A cored slimhole program through the 515–840 m gas-saturated section at Cedar Point, with gas content/desorption testing (never done — the 2001 program measured permeability only, and only once), gas composition analysis and modern stress characterisation. What it achieves: a certifiable gas-in-place number for the unconventional play, in an overpressured setting where the 2001 data already prove saturation and artesian pressure support.

3. The Grafton–Clifden structure — finally reach the horizon that blew out in 1902. A single modern well on the Clifden Dome through the full Bundamba section to the Grafton No. 1 blowout equivalent (~3,100 ft) and into the Gatton Sandstone, preceded by reprocessing of the 1980s seismic to map the dome at target depth (the old wells prove surface mapping doesn't project to depth here). What it achieves: opens a second production hub, tests the deeper untouched Gatton play, and converts the basin story from "one dome that flowed" to "a multi-structure fairway" — the difference between a project and a province.

Closing statement:

• Not a JORC-compliant statement; historical results reported from open-file sources and not verified by a Competent Person.

• All data sourced from publicly available NSW DIGS open-file records and public ASX disclosures.

• This article is general information only and not investment advice

• Full technical synthesis, intercept overview, drill plan and source register available on request.