O.D.N.L. Penola No. 1 Well, located in the north-east corner of Section 500, Hundred of Penola, South Australia, was drilled by Oil Development N.L. under a "farm-out" agreement with General Exploration Company of Australia Limited to a total depth of 4985 feet. Drilling was commenced on 7th February, 1961, and the well was abondoned as a dry hole on 5th May, 1961. The drilling contractor was Australian Tube Wells Pty Ltd, and the rig used was a Failing 2500 - Holemaster. The operation provided for a programme of electric and mud logging, testing and coring.
The Penola Well was designed to test the petroleum potentialities of the Coonawarra subsurface structure, which was first detected by a single reconnaissance seismic reflection traverse made through the Penola area. Beneath a thin Pleistocene cover Penola No. 1 penetrated a sequence of marine and paralic Tertiary, and marine and non-marine Mesozoic rocks, ranging in age from Oligocene to probable Upper Jurassic. The Tertiary sediments consisted of 215 feet of Gambier Limestone (Oligocene); 160 feet of Compton Conglomerate (Oligocene); followed by about 630 feet of paralic sands and grits of the Knight Group (middle to upper Eocene).
There is a marked discontinuity at l040 feet where the well passed abruptly from the Eocene to Cretaceous arkosic sandstones and siltstones of the Merino Group. The Upper Member of the Runnymede Formation of Albian to (?) Cenomanian age was 2380 feet thick, and of marine origin in at least the lower 800 feet, between 2586 and 3420 feet. The lower nonmarine member of the Runnymede Formation (? Aptian) was represented between 3420 and 4300 feet. A slight angular unconformity is interpreted at about 4300 feet, below which the well is considered to have entered non-marine mudstones and sandstones of the Mocamboro Member of probable Upper Jurassic age.
Minor showings of gas were encountered at Penola No. 1, none being of commerial significance. No signs of live oil were observed in the well.
