(College of Petroleum Engineering, Youshi University, China, Qingdao, Shandong 266555)

About the author: Lei Guanglun, male, professor, doctoral supervisor, mainly engaged in teaching and scientific research of oil and gas field development. E-mail: leiglun @163.com.

Abstract: Conventional oil and gas production is far from meeting the domestic demand for oil. Among many unconventional oil and gas resources, oil shale has attracted more and more attention because of its huge reserves and development advantages. The production of shale oil is one of the main uses of shale oil. Through the research on the development and utilization technology of oil shale, this paper points out two ways to produce oil shale, and introduces the oil shale mining technology, ground dry distillation method and in-situ mining technology along these two ways. The open-pit mining and underground mining methods of oil shale are introduced. The effects of heating temperature, heating time and heating speed on the dry distillation yield of shale oil were studied through experimental simulation. The experimental results show that the heating temperature is about 500℃. Heating time reaches1h; The heating speed has little effect on the oil yield. The output, operation rate and oil yield of ground carbonization equipment such as Fushun producer furnace, Kievit furnace, Petelaud Essex furnace, Glot furnace and Tasek furnace are compared, and the characteristics and applicability of various carbonization equipment are analyzed. The principles and technical characteristics of oil shale in-situ mining technologies such as Shell ICP technology, ExxonMobil ElectrofracTM technology, IEP fuel cell technology, PetroProbe air heating technology and Raytheon RF/CF technology are expounded. It is pointed out that the mutual penetration, synthesis, integration and application of various technologies are the development trend of oil shale in-situ mining technology, and the realization of large-scale, low-cost and high-efficiency mining is the important development direction of oil shale in-scale, low-cost and high-efficiency mining.

Key words: oil shale; Shale oil; Mining technology; Ground dry distillation; In-situ mining

Technical progress of oil shale production

Lei Guanglin, Yao Chuanjin, Sun

(School of Petroleum Engineering, China Shiyou University, Qingdao 266555)

Abstract: Conventional oil and gas production can't meet the domestic demand. Among many unconventional resources, oil shale has attracted more and more attention because of its huge reserves and development advantages. Shale oil production is one of the main uses of oil shale. On the basis of studying the exploitation and utilization of oil shale, this paper puts forward two ways to produce oil shale, and introduces the techniques of oil shale exploitation, dry distillation and in-situ exploitation. The methods of open-pit mining and underground mining are described. The influencing factors of shale oil recovery, including heating temperature, heating time and heating rate, were studied by experimental simulation. The results show that the optimum heating temperature and heating time are 500℃ and 65438 0 h, respectively, and the heating rate has little effect on it. The processing capacity, activity rate and shale oil recovery rate of oil shale retort equipment were compared, including Fushun retort, Kiviter retort, Petrosix retort, Galoter retort and ATP retort. This paper introduces the mechanism and characteristics of oil shale in-situ mining technology, including ICP, ElectrofracTM, IEP fuel cell technology, air heating of PetroProbe and RF/CF technology of Raytheon. Based on the penetration, combination and application of high technology, the development trend of oil shale in-situ mining is large-scale, low-cost and high-efficiency.

Key words: oil shale; Shale oil; Mining and use; Open pit mining in situ mining

introduce

As early as 1830, human beings began to develop and utilize oil shale. After 1890, the oil shale industry shrank rapidly due to the rapid development of the oil industry. The utilization of oil shale in China began at 1928. In 1950s and 1960s, shale oil was one of the three pillars of synthetic liquid fuel in China. After 1960, the discovery and exploitation of Daqing Oilfield and Shengli Oilfield made China's oil shale industry enter a stagnant stage.

After entering the 2 1 century, international oil prices continued to rise. In July 2008, the international oil price reached an all-time high of 149 USD/barrel. On the other hand, the contradiction of insufficient domestic oil supply has become increasingly prominent, which has become the "bottleneck" of China's economic development. According to the domestic oil and gas resources and production capacity, the gap between supply and demand will become larger and larger in the future, oil imports will continue to increase, and the risks brought by the increase of external dependence will become heavier and heavier. Among many methods to ensure the supply of liquid fuel, shale oil is a more realistic alternative energy source for oil. According to the statistics of the Ministry of Land and Resources, the predicted oil shale resources in China are 720 billion tons, which is converted into shale oil of 47.6 billion tons [1]. Therefore, large-scale exploration and development of oil shale is of great significance to alleviate the pressure of domestic oil and gas supply and demand.

At present, the mining technologies of oil shale mainly include open-pit mining, underground mining and in-situ mining. Among them, there are two main ways to make shale oil: (1) mining oil shale ore to the ground, and then dry distillation on the ground; (2) Oil shale is dry distilled underground by underground heating technology to produce shale oil [1, 2]. This paper introduces the present situation of oil shale mining technology from these two aspects, and points out the future development trend.

1 oil shale mining technology

1. 1 open pit mining technology

Open-pit mining refers to the method of stripping the earth and stone covering the ore body, dividing the ore body into several steps from top to bottom, and directly open-pit mining. The first condition that must be considered in open-pit mining is the buried depth of oil shale, which generally does not exceed 500m·m m. In addition, stripping ratio should be considered, that is, the ratio of the amount of stripped rock and soil to the amount of exploitable shale when covering shale is an important factor in the economy of open-pit mining. If the oil shale is thin and the rock and soil covered on it is thick, that is, the stripping ratio is large, even if the oil shale is buried deeply, the oil shale mining cost will be high.

The main processes of open-pit mining are: rock perforation, blasting, mining and loading of rock, soil and oil shale, and transportation of rock, soil and oil shale. Blast hard rock and medium hard oil shale with drilling rig to facilitate excavation. If there is no hard stratum, it may not be necessary to drill and blast. Rock, soil and oil shale can be collected and installed with single bucket excavators, wheel bucket excavators, bucket excavators and other mining and stripping equipment. At present, oil shale is mined in the open pit. For mining areas with thin overburden, thick oil shale layer and small stripping ratio, the mining cost per ton of oil shale in China is about 40 ~ 80 yuan under different conditions.

Figure 1 Schematic Diagram of Longwall Mining Method

1.2 underground mining technology

Underground mining of oil shale refers to entering underground working face through shaft and transporting oil shale to the ground. The underground working face is the working place of oil shale mining, where the processes of oil shale mining, transportation, support and goaf treatment are carried out. It mainly includes wall mining method and room and pillar mining method [1].

1.2. 1 wall mining method

Wall mining method is divided into short-wall working face and long-wall working face. The length of short-wall working face is generally below 50m, which is mostly used in small mines. Longwall working face is long, generally exceeding 100m. The picture shows the schematic diagram of longwall mining method. Return air drift and transportation drift are respectively arranged above and below the working face along the strike, forming ventilation, transportation and pedestrian passages between the working face and the mining area.

1.2.2 room and pillar mining method

Room-and-pillar mining method refers to digging out rooms from the mining roadway at regular intervals to mine oil shale, leaving oil shale pillars to support the roof. The columns are round, rectangular or strip-shaped and arranged regularly. Generally, the room width is 6 ~ 12m, and the column width is 3 ~ 6m. When the roof stability is slightly poor, the ore value is low, or the mined-out area is used as an underground building after mining, the strip continuous pillar is used. Pillars are generally not recovered, accounting for 15% ~ 40% of the total ore volume. Because the room and pillar mining method is not safe enough, its application is less and less.

2 oil shale dry distillation process

2. 1 Factors affecting the dry distillation of oil shale

At present, the production of shale oil is mainly realized by dry distillation of shale oil. Dry distillation of oil shale is a method of heating to a temperature of about 450 ~ 550℃ under the condition of air isolation, and pyrolyzing it to generate shale oil, shale semi-coke and pyrolysis gas. The main factors affecting shale oil yield are heating temperature, heating time and heating speed. In this paper, the influence factors of dry distillation were studied by using Jinge dry distillation test device and taking Fushun typical oil shale as an example.

2. 1. 1 Influence of heating temperature

Fushun oil shale with particle size of 1 ~ 2mm was heated to different temperatures at a heating rate of 5℃/min, and heated at a constant temperature for 5 hours, and then the shale oil yield was determined at this constant temperature. The test results are shown in Figure 2:

As can be seen from Figure 2, with the increase of constant heating temperature, the yield of shale oil obtained by decomposition increases continuously. However, when the temperature rises to 500℃, the temperature rises further, and the increase of shale oil yield is not significant. The table shows that when the temperature reaches 500℃ and the constant temperature is 5 hours, the pyrolysis reaction is basically completed, and the temperature required for shale oil production is not high, about 500℃. Excessive temperature will lead to the decomposition of crystal water contained in minerals, thus consuming a lot of energy. Therefore, in order to obtain shale oil, the final heating temperature of Fushun oil shale dry distillation is 500℃.

2. 1.2 Effect of heating time

Fushun oil shale with particle size of 1 ~ 2mm was heated at a heating rate of 2℃/min. The relationship between heating time and shale oil yield at different temperatures is shown in Figure 3.

Fig. 2 Effect of heating temperature on shale oil yield

Fig. 3 Effect of heating time on shale oil yield

As can be seen from Figure 3, before the heating temperature is 375℃, the release of shale oil always increases with the extension of heating time. However, at 450℃, shale oil will not be released after heating for more than 65438±0h h. This shows that the pyrolysis reaction of organic matter has been completed. Therefore, the higher the heating temperature, the faster the decomposition rate of organic matter in oil shale and the shorter the time required to reach the maximum shale oil yield. If the pyrolysis temperature is above 500℃, the thermal decomposition reaction of organic matter can be completed in a short time, but the heating time has no obvious effect on the shale oil yield. Therefore, the final heating temperature is the main factor affecting the thermal decomposition reaction.

Fig. 4 Effect of heating speed on shale oil yield

2. 1.3 Effect of heating speed

Fushun oil shale with particle size of 65438±0～2mm was heated to 500℃ at different heating rates and kept for 65438±0h. The relationship curve between different heating rates and shale oil yield is shown in Figure 4.

As can be seen from Figure 4, when the heating rate is increased from 2℃/min to 20℃/min, the shale oil yield is slightly increased, but the amplitude is very small. Therefore, when designing retorting equipment, the method of intensified retorting can be used to increase the heating speed and make the oil shale reach the specified final temperature quickly. This can greatly shorten the dry distillation time and improve the efficiency.

2.2 Ground dry distillation equipment

Ground dry distillation of oil shale is mainly realized by dry distillation furnace. The technical indexes of retort mainly include oil yield, annual operating rate and adaptability. At present, the more mature furnace types in the world mainly include Fushun producer furnace, Kievit furnace, Petelaud Essex furnace, Glot furnace and Tasek furnace [3 ~ 6]. See table 1 for the parameter comparison of dry distillation equipment.

Table 1 Comparison of Oil Shale Dry Distillation Equipment

Fushun-type producers in China have smaller production capacity, lower oil output and less advanced technology for processing massive shale compared with laboratory aluminum retorts. However, it is a mature furnace type, which can handle lean ore, has good operation flexibility, long operation experience, less investment and fast construction, and is suitable for small factories. Although Fushun furnace has a small capacity, 20 furnaces are combined into one furnace, and the daily output of oil shale in one furnace can reach 2000 ~ 4000 tons.

The Kievit furnace in Estonia has a large capacity, and the oil yield of shale is not too high compared with that of aluminum retort. It belongs to mature furnace type and is under investment, which is suitable for medium-sized plants.

Brazil's Petelaud Sikes furnace has a large capacity, which can treat massive shale. Compared with aluminum retort furnace, it has a high oil yield and produces high calorific value gas. It is a mature furnace type with high investment and is suitable for large and medium-sized factories.

Glot furnace in Estonia has a large capacity and can handle granular shale. Compared with aluminum retort furnace, it has high oil yield and high calorific value of gas. However, it has complicated structure and high maintenance cost. It is a basically mature furnace type. It is reported that it can be used in large and medium-sized factories with an annual operation of 7200h·h h.

Australia's Tasek furnace has a large capacity, which can treat granular shale, with high oil yield and high gas calorific value. After shale oil hydrogenation, the quality is good and the investment is high, but it is not mature enough. Before the shutdown in 2004, the operating rate was only 50%, so large and medium-sized factories can consider adopting this technology.

3 In-situ mining technology

In-situ mining technology refers to the technology of dry distillation of oil shale underground by underground heating, and then exporting the generated shale oil and gas to the ground. According to the different heating methods of oil shale layer, in-situ oil shale mining technology can be divided into three types: conduction heating, convection heating and radiation heating. See Table 2 [7 ~ 9] for the advanced in-situ mining technology at present.

Table 2 In-situ Mining Technology Table

3. 1 shell ICP technology

Shell ICP technology is the only in-situ mining technology that has been tested in the field. The main principle is that the heat is transferred to the underground oil shale layer by an electric heater for heating and cracking, so that kerogen in the oil shale can be converted into high-quality oil and gas, and then the oil and gas can be extracted to the ground through a production well (Figure 5). The technological process mainly includes: firstly, build a freezing wall to prevent formation water from flowing into the mining area and prevent the loss of oil and gas products. Secondly, an electric heater is installed in the heating well to heat the oil shale layer. Finally, dry distillation oil and gas are extracted, and parameters such as hydrology, geology, temperature, pressure and water quality are monitored.

Fig. 5 schematic diagram of ICP technology

Characteristics of ICP technology: (1)ICP technology has uniform heating and low heating temperature, which can develop deep low oil shale; (2) Frozen wall can protect groundwater resources; (3) The heating process is complicated, with many obstacles, low recovery rate and high cost.

Since 1997, Shell has conducted many experiments in mahogany, Colorado. From 2004 to 2005, the results of a test area showed that the heating rate was 2℃/d, oil production began in May 2004, reached the maximum in June 2004, and then decreased, and oil production ended in June 2005. The total oil production is 250 tons, accounting for 68% of Al Zan.

3.2 Exxon-Mobil voltage splitting technology

Exxon-Mobil ElectrofracTM technology firstly uses parallel horizontal wells to hydraulically fracture shale, and then fills the cracks in the oil shale coal seam with conductive medium to form a heating unit. The heat-conducting medium transfers heat to shale through conduction, which pyrolyzes kerogen in shale, and the generated oil and gas is collected to the ground through oil wells (Figure 6).

Fig. 6 schematic diagram of voltage splitting technology

Characteristics of voltage fracturing technology: (1) Using fracturing technology to improve shale permeability and exploit tight oil shale resources; (2) By-product sodium carbonate improves economic benefits; (3) Adopting the linear heat conduction formula of plane heat source to effectively improve the thermal efficiency; (4) Without groundwater protection, it is easy to cause water pollution.

3.3 IEP fuel cell technology

The reaction heat of high-temperature fuel cell stack is used to directly heat the oil shale layer, so that the organic matter in it is pyrolyzed to generate hydrocarbon gas, which is then introduced into the oil well and pumped to the ground. Except for a part of the gas introduced into the fuel cell stack as fuel, most of the remaining hydrocarbon gas is condensed to obtain oil and natural gas. In addition, during the preheating of oil shale in the start-up process unit, it is necessary to introduce natural gas into the fuel cell as the start-up fuel. After the normal operation of the process, the energy is self-sufficient.

Technical characteristics of IEP fuel cell: (1) The temperature distribution of conduction heating is uniform. Heat is transferred through heat conduction between solids, which greatly improves the uniformity of heat distribution and utilization efficiency; (2) fluid fracturing and fracture-making to improve the porosity and permeability of oil shale layer; (3) Energy self-sufficiency. This process is not only energy self-sufficient, but also can provide electric energy to the outside world. For every oil produced 1 barrel, the power generation is174 kw h; (4) Low operating cost. The operating cost is about $30/barrel. If the by-products of electricity and natural gas are included, the cost can be reduced to $65438 +04/ barrel; (5) Environmental protection. Because this process does not generate electricity through combustion reaction, but through electric reaction, it hardly produces harmful substances such as nitrogen oxides and SO2 (Figure 7).

Fig. 7 schematic diagram of IEP fuel cell technology

3.4 PetroProbe air heating technology

The process flow is as follows: firstly, compressed air and dry distillation gas are introduced into a burner for combustion, heated to a certain temperature, and part of oxygen is consumed; Then, compressed air and dry distillation gas are introduced into the oil shale formation to heat the oil shale to generate hydrocarbon gas; Finally, the generated hydrocarbon gas is brought to the ground. The produced hydrocarbon gas is condensed to obtain light oil products (Figure 8).

PetroProbe's air heating technology features: (1) The injected high-temperature compressed air can rupture the oil shale in the formation, increase the porosity of the oil shale, and make the generated hydrocarbon gas easily exported from the oil shale formation; (2) There are four products in this process: hydrogen, methane, light oil and water. Part of the generated light hydrocarbon gas is sent to the burner for combustion, which heats the air sent to the formation and is self-sufficient. The produced carbon dioxide and other gases are pumped back to the oil shale layer with little pollution, which can be used to develop deep oil shale ore (up to 900 meters deep). (3) After mining, the oil shale can still maintain the original structural integrity of 94% ~ 99%, thus avoiding ground collapse.

3.5 Raytheon RF/CF technology

Raytheon's RF/CF (Radio Frequency/Critical Fluid) technology is a patented conversion technology using radio frequency heating and supercritical fluid as carriers (Figure 9). The process flow is as follows: firstly, the RF transmitter is placed in the underground oil shale layer for heating, then supercritical CO2 is introduced into the shale layer, and the hydrocarbon gas generated by pyrolysis is carried to the oil production well, and pumped to the ground for condensation and recovery. The condensed CO2 is returned to the formation for recycling.

Fig. 8 schematic diagram of air heating technology

Fig. 9 schematic diagram of RF/CF technology

Technical characteristics of RF/CF: (1) high oil recovery. For every 1 unit energy consumed, 4 ~ 5 units of energy are generated, which is more economical than 3.5 units of ICP technology. (2) fast heat transfer and short heating cycle, only a few months; (3) When it is used for oil shale exploitation, the produced oil has low sulfur content, and different products can be produced by regulating devices; (4) It can be used to exploit oil shale, oil sands, heavy oil and other resources. Environment-friendly, and no residual substances penetrate into the groundwater layer; (5) Selective heating can make the designated heating target area reach the target temperature quickly.

4 conclusion

(1) At present, the main ways to prepare shale oil are mining-ground dry distillation process and in-situ mining technology. The former technology is relatively mature, while the latter is still in the stage of experimental verification.

(2) Experimental research shows that the suitable temperature for oil shale retorting is about 500℃ and the retorting time is 65438±0h. Heating speed has little effect on shale oil yield. In industrial production, the method of intensified dry distillation can be used to improve the heating speed, so that the oil shale can reach the specified final temperature quickly and improve the efficiency.

(3) At present, there are some problems in the ground dry distillation device, such as small capacity, low operation rate and low oil yield, which need to be further optimized.

(4) With the goal of large-scale, low-cost and high-benefit, the mutual penetration, synthesis, integration and application of various technologies is the main direction of the development of in-situ mining technology.

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