CA2397574A1 - Method of barge mining tar sands - Google Patents

Abstract

Tar sands are flooded and then dredge mined via barges. The process ensures the tar sands do not freeze, making excavation easier during the winter months, and reducing slowdowns due to frost lumps. The process also eliminates the need to use trucks in the mining pits, resulting in an overall reduction in costs.

Description

METHOD OF BARGE MINING TAR SANDS
Field of the Invention This invention relates to the mining of tar sands for the purpose of extracting oil therefrom.
Background of the Invention The Athabasca tar sands consist of vast areas of sand infused with bitumen.
The sand is often overlain by various types of overburden such as muskeg, clay, sand, gravel, fill and lean tar sand. Limestone bedrock typically lies underneath the tar-sand, but sometimes coal is the underlying material.
Where possible, the tar sand deposits are harvested by open-pit mining. The overburden is stripped off and used for various purposes. Muskeg is often stockpiled separately for future land reclamation, some materials are used to construct haul roads or dykes for tailing ponds, and the remaining materials are placed in waste dumps.
Following the stripping, the tar sands are excavated and delivered to sizers that break down any large lumps. The ore is then conveyed to a coarse ore stockpile, or surge.
It is fed from the surge via a reclaim conveyer to the preparation plant, where it blended with hot water and agitated to form a slurry. The slurry is pumped to an extraction plant. In older operations, the surge may be eliminated; the sized material is fed directly to the preparation plant via a conveyer.
At the extraction plant, bitumen is separated from the sand. The bitumen is then pumped to an upgrader for processing, while the sand and water are pumped back to tailing ponds, usually mined-out pits.

The mining of tar sands and extraction of bitumen is a very costly process.
Four reasons for the high costs are the use of trucks, the use of ground-engaging tools, the need for ripping and blasting during the winter, and the blocking of the conveyances by frozen lumps of sand.
Tar sands are difficult to drive on once disturbed, since it has little shear strength and tends to become badly rutted. Trucks have trouble getting through it even in good weather, and in wet weather they often become stuck. Sand and limestone are often used to strengthen frequently-travelled areas; this is not only costly, but has only limited success.
Tar sands are very abrasive, and tightly packed. Digging is therefore very costly, as ground-engaging tools must be frequently replaced.
During the winter, most of the tar sands are frozen, necessitating expensive ripping, drilling and/or blasting. In addition, the coarse ore piles downstream of the sizers frequently become plugged with frost lumps. The sizer must then be stopped, and the surge piles excavated. Older feed systems without surges have continual spillage of rocks and frost lumps, causing costly clean-up year-round, and especially during the winter.
A less costly method of mining tar sands is required.
Summary of the Invention An object of the present invention is to provide a reduced-cost method for mining tar sands.
The tar sand pits are flooded with water and mined in a series of cells with dredging barges rather than trucks. The overburden may be stripped prior to the flooding by traditional methods, or after flooding, by dredging. The low permeability of tar sand minimizes leakage and reduces the likelihood of environmental damage. If necessary, permeable areas can be sealed with membranes, grout or even bitumen.

The barges are fitted with conventional dredging equipment, such as a cutter-head system for loosening tightly packed material. The excavation proceeds in horizontal layers at the bottom of the pond, the water level being regulated by pumping water back and forth between the mining pond and tailing ponds.
With the use of barges, the need for trucks to drive on unstable tar sands for excavation purposes is eliminated or reduced. This translates into savings in cost.
Once each cell has been mined down to the bedrock level, it is reflooded to allow the barge to navigate into the next cell and begin excavation. A number of cells may operate concurrently at various stages of completion, with one or more dredges operating in each.
In this way, ore grade may be controlled by adjusting and blending flows from different depths, and throughput can be maintained by having spare capacity to handle moves, breakdowns and refits.
Berms left between cells may be mined later by truck and shovel or by dredge.
Completed cells are used for tailings and waste disposal. Discharge pipes from the dredges are floated in the ponds during the summer months, and carried by the ice during the winter.
Once extracted, the ore is pumped to the mixing plant for further processing, or directly to the extraction plant via a pipeline downstream of the mixing plant.
A distinct cost advantage of this process is the delivery of warm material during the winter.
The ore being mined will be kept flooded with water, so that its temperature will never be lower than 0°C. This may make a difference of up to 30 or 40°C
compared to current practices.
The recent practice of pumping the tar sand in warm slurry to the extraction plant has the advantage of causing a partial separation of sand and oil particles in the pipeline en route to the extraction plant. The dredge mining method enhances this effect by increasing the distance of slurry travel from the pit itself all the way to the extraction plant.
In order to increase slurry temperature, the mined slurry may have to be partially dewatered at the preparation plant, with surplus water being returned to the pit and additional hot water being added to the sand for the journey to the extractor. Alternatively, warm tailings water may be piped directly to the cutter head, or a reduced-scale heating and mixing system may be installed on the barge. In any case, there is a reduction in energy costs due to the higher average ore temperature.
Further savings are realized through a lowering of ore cut-off grade. Since the cost of mining is significantly reduced with this method, it becomes cost-effective to mine a lower grade of ore. Accordingly, more of the lean tar sand may be classified as ore, thus enlarging the reserve and lowering the amount of stripping required.
Overall, significant cost reductions in the order of $2.00 per barrel are anticipated.
Brief Description of the Figures Figure 1 is a flow chart illustrating the traditional open-pit mining method (prior art).
Figure 2 is a flow chart illustrating the flooded-pit dredging mining method.
Detailed Description of the Figures In Figure 1, the pit (1 ) is excavated with heavy-duty ground-engaging equipment (2). Ore is transported by trucks (3) to a sizer (4) for breakage of large ore lumps.
The ore is conveyed to a surge (5), and then is conveyed to a preparation plant (6) where it is mixed with water to form a slurry. The slurry is pumped to an extraction plant (7), where sand and bitumen are separated. Bitumen is pumped to an upgrader for processing, while sand and water are pumped to tailing ponds.
In Figure 2, the pit (1 ) is filled with water (8) and excavated with a dredge (9). The ore, along with some water, is conveyed directly to a preparation plant (6), where the cooler water may be replaced with hot water. The slurry is pumped to an extraction plant (7), where sand and bitumen are separated. Bitumen is pumped to an upgraderfor processing, while sand and water are pumped to tailing ponds.

Claims (4)

1. A method for mining tar sand from an underground tar sand deposit comprising:
a) removing ground materials above said underground tar sand deposit to form a pit;
b) filling said pit with water;
c) extracting said tar sand from said pit by means of a dredge; and d) transporting said extracted tar sand out from said pit for further processing.

2. A method for mining tar sand as claimed in claim 1, wherein said extracted tar sand is transported out from said pit to an extraction plant in the form of a slurry.

3. A method for mining tar sand as claimed in claim 2, wherein said slurry is at a temperature higher than the temperature of the water in said pit.

4. A method for mining tar sand as claimed in claim 1, wherein steps a) and b) are performed concurrently.