Date Published: June 20, 2018
Publisher: Public Library of Science
Author(s): Jiwei Wen, Chen Chen, Urso Campos, Xiao-Jun Yang.
Oil shale is an unconventional energy source, and it is also a potential petroleum substitute. Nowadays, the energy shortage is becoming more and more prominent, oil shale has attracted the attention of energy researchers all over the world. Borehole hydraulic mining is an effective method to exploit the underground oil shale which has more prominent advantages than other conventional mining methods. Jet devices are the key component of borehole hydraulic mining, which include the straight cone nozzle, organ pipe nozzle and self-excited oscillation pulsed jet nozzle. Also, the reasonable mining parameters are also crucial in mining underground oil shale efficiency. The jet characteristics of the non-submerged water jet, submerged water jet, direct water jet, cavitating water jet, and pulsed water jet are also explained and compared based on theoretical analysis. The jet performance of the non-submerged water jet is better than the submerged water jet. Each type of jet devices has its own basic principles and optimal structural parameters. The best operating scheme of borehole hydraulic mining for underground oil shale is to use the pulsed water jet which is produced by the self-excited oscillation pulsed jet nozzle to break underground oil shale under the non-submerged condition. Moreover, the pulsed water jet should be placed parallel to the oil shale bedding. In addition, under the preconditions of ensuring the safety and reliability of the hydraulic mining equipment and pipelines connection, the jet pressure and jet flow should be raised as much as possible, so as to obtain the much higher mining efficiency. These results and conclusions can provide very valuable guidance for borehole hydraulic mining of underground oil shale.
There is no doubt that energy has always been one of the substances closely bound up with human daily life. The four essential requirements of the human: clothing, food, housing, and transportation are all dependent on energy. In addition, the development of societies, economies, national security, and stability are also inseparable from energy . The unconventional oil and gas resources such as: oil shale, shale gas, methane hydrates, coalbed methane, tight gas sandstone, etc., have been gaining more and more attention worldwide in recent years with the fluctuating global oil prices . Oil shale, in particular, has been widely utilized as a supplement to conventional energy resources because of the large reserves of oil shale, and its applicability in different fields such as: building and chemical materials industries, agriculture, medicine, environmental protection, etc. [3–8].
High-pressure water jet technology uses water as the work medium. The high-pressure energy of water is attained by using high-pressure pumps. Furthermore, the energy concentrated liquid column, that is the high-pressure water jet, is ejected from the outlet of a nozzle at high speed after the high-pressure water continuously flow past the internal flow channel of the nozzle [15–27]. Some of the many advantages of using a nozzle include: cleanliness, concentrated cutting energy, consistency in water jet output, and reduction of sparks and sharp rubbles resulting in a safe cutting process. In addition, it can also be combined with a numerical control machine tool to precisely cut arbitrary and complex shapes. High-pressure water jet technology has been widely used in many industry fields such as: coal, metallurgy, petroleum, municipal, etc. Some of its specialized applications include: mining, drilling, cleaning, surface treating, industrial cutting, etc. Conclusively, it has resulted in many remarkable social and economic benefits.
The water jet performance can be evaluated by its striking force. Under the same experimental conditions, the greater the striking force, the better the water jet performance of the nozzle. Moreover, the breaking of oil shale not only can be used to evaluate the water jet performance of the nozzle, but also can be used to propose the parameters of the borehole hydraulic mining for oil shale. Therefore, the aim of this experimental study focuses on the comparison of the striking forces and the breaking oil shale effects of three different nozzles. (dx.doi.org/10.17504/protocols.io.ppfdmjn)
As discussed above, in the process of the borehole hydraulic mining for underground oil shale, the most critical step is using high-pressure water jet which is ejected by the jet device to break the underground oil shale into several small pieces and then peel them off from the parent rock. Moreover, in the case of using only a borehole to implement the borehole hydraulic mining for underground oil shale, the farther the effective water jet distance to break oil shale, the greater the scope of the mining. That means the more oil shale can be mined based on a same borehole. Also, the ability of high-pressure water jet to break the oil shale has crucial influence on the efficiency of the borehole hydraulic mining for underground oil shale. This also means the cost of the borehole hydraulic mining for underground oil shale will be lower. Therefore, to explore a jet device which has excellent water jet performance is very important and meaningful.