Athabasca Project -- History
The Alberta bituminous sands terrane in the Fort McMurray area is one of the regions studied by C. Warren Hunt in developing his ideas respecting deep-Earth sources for hydrocarbons. This is thoroughly discussed in his book "Expanding Geospheres" for those who wish to pursue the matter completely (www.polarpublishing.com). For the purposes of this report the writer will attempt to summarize the pertinent features.
The Athabasca Tar Sands deposit is one of the largest accumulations of petroleum on earth, some 1.3 trillion barrels, and covers an area of 28,000 square kilometers. It is situated on the western side of the Athabasca sand debouchment, which was deposited during middle Proterozoic time some 1.3 billion years ago and it covers an area of some 75,000 square kilometers. It is thought that these quartz sands were deposited as an extrusion from the Carswell crater when effusing silanes encountered near surface water to form the silica sand that was convulsively exhaled from the vent. This would have been an eruption of unheard of proportions by modern day standards. The crater is some 20 km. in diameter. The flow of silica material was to the east of the crater and the shear weight of the deposit (some 50000 cubic kms.) caused a subsidence or bowing in the underlying Precambrian granitic crust to form a bowl 1200 metres deep west of a dome with its crest in the general area of Ft. McMurray. From there the basement rocks dip to the west. It is believed that a huge amount of hydrocarbon material was released during this event but that a significant amount would have been trapped beneath the area west of the Carswell crater as a result of the trap or dip reversal that was created by the subsidence of the basement to the east.
Now fast forwarding to Cretaceous Mannville time which commenced 180 million years ago, we have the deposition of a sand shale sequence taking place and subsequent leakage through fractures in the underlying basement rocks of the hydrocarbons trapped at the time of the Carswell event. The crest of the dome in the Fort McMurray area is known to be fractured, and is defined by a trough or graben that runs through the area. Escapement of hydrocarbons through the fractures below the graben into the McMurray sands, and subsequent biodegradation has resulted in the huge 1.3 trillion barrel oil deposit now being exploited by industry. However, this still leaves the underlying source hydrocarbons that have been leaking toward the surface through the granite basement rocks and the potential for oil accumulations trapped in the granite material in fracture reservoirs. Hence, the Athabasca Oil Prospect is born.
A seismic line run across the granite dome identified a number of fracture systems that appear to be quite thick, the shallowest of which is at around 2150 meters. In Sept. 1994 a group put together by C. Warren Hunt commenced the drilling of a well aimed at finding hydrocarbons in the basement granite rocks, which commence at 550m. Licensed as AOC Granite 7-32-89-10W4, the well was situated 4 km. west of Fort McMurray, Alberta over the crest of the seismically reflective zone at 2150 meters or 7050 feet.
The granite was encountered at 543 meters and during drilling from 803m-837m high gravity crude oil shows were collected on 5 separate occasions from the drilling mud. A drill stem test was run from 800m to the bottom of the hole at 837m but failed to indicate the presence of a reservoir. Subsequent logging of the hole indicated the presence of a 4m fracture zone between 790m and 794m which was above the test interval. The oil shows can be attributed to this zone. The well was taken down to 1649m where a gas show was encountered. At this point on Oct. 8, 1994, some 36 days after commencing drilling, the well had to be suspended due to a lack of investor funds. A suite of logs was run identifying additional fracture zones at 865-900m., 1410-1479m.and at 1647m. The bottom zone also coincided with a transition from granite rocks to gabbro. The lack of funding resulted in the failure to reach the seismic event at 2150m.as originally envisioned.
One of the logs that were run, an FMI log, presents a visual picture of the well bore and the fracture patterns mentioned above can be clearly seen. This log allows one to make measurements to determine the dip and strike of the fracture and/or fault patterns encountered in the well. Analysis shows the fractures to be steeply dipping, in fact at as high as an 84° angle to the well bore, which is the case of the fractures at 790-794m. If these fractures extend for any distance from the well bore, there is a good possibility that they are connected to the seismically interpreted major fracture pattern at the 2150m level or deeper ones. In this event the steeply dipping fractures intersected by drilling would provide an excellent conduit for oil and/or gas into the well bore. Validating this possibility is precisely what is proposed as the first step in evaluating the 7-32 well.
The drill cuttings that were collected from the well exhibited oil staining across each of the fracture zones. Recently the cuttings were subjected to a Fluid Inclusion analysis and hydrocarbon inclusions were present in all of the drill cuttings collected across the fracture zones and their proximal capping tight granites, but not in the cuttings taken from the remainder of the "tight" granite section from 543m to TD. These results add strong support to the probability that hydrocarbons are present. |
