It is known to extract high-viscosity and bitumen-like crude oils (e.g., oil sands) by strip mining. This method is frequently put into practice in regions where such deposits have been developed or are covered by less than 75 meters of sediment.
For underground deposits, starting from a depth of about 75 meters, use is frequently made of “in situ” methods. With this technique, the oil sand (e.g., the sand and the rock with the oil contained therein) remains in place within the original formation. The oil or bitumen is separated from the sand grain by various processes and is made more flowable so that it may be extracted. The general principle underlying the “in situ” methods is to increase the temperature in the subsurface, thereby lowering the viscosity of the bound oil or bitumen and making the bound oil or biumen more flowable so that it may subsequently be pumped out. The effect of the heating action is to split up long-chained hydrocarbons of the highly viscous bitumen.
Well-known methods based on “in situ” methods are SAGD (steam assisted gravity drainage), CSS (cyclic steam stimulation), THAI (toe to heel air injection), VAPEX (vapor extraction process), etc.
The most widespread and applied “in situ” method for recovering viscous oils and bitumen is the SAGD method. For example, with this technique, steam is forced in under pressure through a well running horizontally within the reservoir, the well being equipped for that purpose with a special slotted injection pipe. The heated, molten bitumen/heavy oil, having been separated from the sand or rock, seeps to a second slotted pipe (e.g., the production pipe) that has been introduced into a horizontal well located roughly 5 meters deeper (e.g., the distance between injector and production pipe, depending on reservoir geometry) and through which the liquefied bitumen/heavy oil is conveyed. During this process, the steam fulfills a number of tasks simultaneously (e.g., introducing the heating energy to achieve the liquefaction, separating the bitumen/oil from the sand, and building up the pressure in the reservoir in order to make the reservoir technically permeable to allow the bitumen to be transported (permeability) and to enable the bitumen to be extracted).
In the SAGD method, two technological phases are typically to be performed in succession: a steam circulation phase over several months; and followed by a production phase (e.g., SAGD phase), where the steam injection is continued.
While the aforementioned methods are provided for permeable sands, there are also oil deposits where high-viscosity oils and bitumen are trapped in low-permeability or partially permeable rock, or trapped in alternating layers of permeable and non-permeable rock, such that exploitation by mining techniques is conceivable.
Oil recovery using mine workings is known from U.S. Pat. No. 4,458,945. As well as the operation explained therein (e.g., oil is conducted away by pipes), it is also mentioned that in order to enhance recovery of the oil, it would be possible to utilize radio waves or microwaves that penetrate into an oil sand stratum to increase the flowability of the oil.
A method for oil recovery using mining techniques is known from the abstract of Patent Application No. RU2268356, where steam is injected from a mine tunnel (e.g., shaft) into a zone in order subsequently to extract oil.
If steam or hot water is used as a heat-carrying medium in order to recover crude oil by shaft mining, the following disadvantages may result: a possibility of steam breakthrough into the mine workings, which leads to the loss of the heat-carrying medium and jeopardizes operational safety; high investment and operating costs that result from building/purchasing and operating the steam production facilities; and high overheads for separating the oil-water mixture and high overheads for treatment of the water produced.