Thermal Mining consisted of warming up a layer of crude oil and decreasing its viscosity, which would in turn increase its mobility and extractability. At a temperature of 700C, the viscosity is 109 MPa.s, and at a temperature of 1000C, it is 30 MPa.s.

At the time, there was no practical experience to anticipate the impact of heat on the outer seam of the oil mines. Therefore, for the implementation of the Thermal Mining method to be effective, multiple theoretical and practical problems needed to be solved first. 

Several systems for the position of wells in the seam were developed for the implementation of the Thermal Mining method, including the Double Horizon System, the Single Horizon System, an Underground-to-Surface system, and the potential combination of these systems with one another. 

Oil production was made via dense systems of horizontal and slow uprising underground wells, which were drilled in the mines and driven from the lower segments of the production formation, referred to as the Production Gallery. These three systems differ only in the arrangement of their injection wells.

The Double Horizon System steam injection is conducted through a dense pattern of underground injection wells drilled in the mine workings (or rock gangways), which are established along the oil seam. Steam is pumped through a system of underground steam lines from the steam supply tank to these underground injection wells, forcing the hot air from the surface into the mine workings.

The development of the blocks using the Double Horizon System have performed at a high technological rate. The average ORF in the abandoned blocks in 0,54 with a steam-to-oil ratio of 2,68 t/t. From 1972 to 2007, the Double Horizon System has been utilized in 90 to 95% of mine areas in which the operation has already been established. 

The Double Horizon System differs in its high coefficient of formation coverage with thermal influence, but it also demands a large volume of driven mine workings at 240 m/hectare. In addition to the mine workings, its difficult configuration dictates a complex ventilation system that makes troubleshooting and maintenance more difficult. Also, there are additional thermal emissions in the underground air because of these steam lines that are fed from above the group. 

With the increasing volume of mine excavation projects, the Double Horizon System likely is not a sustainable solution and will not continue to be used.

The Single Horizon System became the leader of surface technology in thermogravitational drainage systems, specific to the oil seam (TGDP or SAGD). 

In 1977, representatives of the Canadian firm “AOSTRA” visited Yarega for a field study, and as a result, the first mine was built on the Atabask field where a Single Horizon System had been established previously. Unlike the Yarega productive depositi, the productive formation of the Atabask deposit was located on anhydrous limestones, and the mine workings had been excavated under the seam at a distance of 15 to 20 meters. This allowed for the issues with thermal conditions to be solved, and further work by AOSTRA has determined the possibility of bringing the wellheads of underground wells to the surface for the SAGD technology to truly become a reality.

During the initial development of the Underground-to-Surface System, steam was injected at the highest possible rate, which led to an intense warming up of the seam. This allowed the team to determine the highest possible rates of crude oil production, as well as the highest achievable steam-to-oil ratio. 

Compared to other systems, the rate of oil production has grown by 1.4 to 1.9 times, and an average of 4 to 5% per year, and the maximum rates have reached 9 to 10%. In 2017, crude oil production with the Underground-to-Surface System exceeded 90% of all oil production. 

With underground wells reaching 300 meters, mine workings for Single Horizon and Undergrand-to-Surface Systems makes up 92 m/hectare with radial, and 57 m/hectare with a panel arrangement of underground wells. With wells at 800 meters, the Systems make up to 28 m/hectare. The Double Horizon System would be 240 m/hectare. 

Implementation of the Underground-to-Surface System has allowed excavation processes to reduce by 8.6 times the mine workings and 8,3 times the volume of underground drilling. 

Below are schematic diagrams of the distribution of heat using the Single Horizon and the Underground-to-Surface Systems. 

Please note that these schematics are incredibly similar, with the primary differences being the use of Thermo-insulating Thread or Regular Thread, as well as the point from which steam is injected either above or below ground. 

Saturated steam pressure of 1,6 MPa with a corresponding temperature of 201 degrees celsius is the value limit for thermal mining development in the Yaregsky field. After 207 degrees celsius is reached, distillation (or cracking) of the oil in the seam occurs, which is detrimental to continued mining development and crude oil production.

The Scheme of the Oil Mine and Crude Oil Production on the Yarega Field of 1932 to 2017

In the above picture, three mine working systems have been depicted. Note specifically the differences in the positionings and direction of the wells, the placement of the mine workings, and the depth of the holes. 

The Above the Seam method is considered to be the worst, as the gravitational energy is not utilized in the extraction of the oil. Similarly, the In Seam method does not utilize gravitational energy as well as possible, and big thermal emissions from the heated seam were experienced. Additional mining structures also could not be placed under the seam at a later date because of the abundance of water that was collected beneath in the process. Under the Seam was considered to be the best of the mining arrangements. Gravitational energy was used effectively, and there were minimal thermal emissions.

In the structuring of mines, the formation will be more successful depending on its use of gravitational energy and its proximity to the oil seam itself, which benefits underground formations. Similarly, the cost significantly diminishes in the formation of underground wells, making them the more logical choice.