National Research Tomsk Polytechnic University, Tomsk, Russia

Abrasive drilling with the jet-type drill bit

F.R. Aliev, D.A. Yakushev, V.M. Gorbenko, A.V. Kovalev

Scientific advisors: associate professor S.Y. Ryabchikov, assistant professor T. F. Dolgaya

National Research Tomsk Polytechnic University, Tomsk, Russia

Today, along with the traditional method of rock failure - mechanical, there are plenty of alternatives. Mechanical way, having a number of significant advantages, in some cases has serious disadvantages, such as the use of expensive rock cutting tools which are technologically complex to be made. This is especially true when we drill hard rocks according to the field classification. The use of water jet - erosive method of rock destruction will greatly increase the efficiency of destruction and allow the specialists to get rid of the mechanical method disadvantages described above.

Drilling Department at TPU designed an abrasive drilling unit with jet-ejection-water type bit [7, 8]. The unit was based on the principle of rock destruction by using continuous circulation of rock-destruction particles at the well bottom. This was carried out by the jet device operated by the stream of the flushing fluid.

The scheme of the jet device for the developed drill bit is shown in the Fig. 1. The device consists of a body (1), a replaceable nozzle (2), and a headpiece with a diffuser (3). The replaceable nozzle allows us in case of necessity to vary its diameter. The replaceable headpiece varies the length of the mixing chamber and the diffusor angle. The operation principle of the unit is shown in (Fig. 2): the flushing fluid, which supplies the device under high velocity, is going through the chamber of the flushing fluid input of (1), it accelerates in the nozzle (2), and at the nozzle exit it flows out with high velocity into the mixing chamber (3). At the same time in the space, which surrounds the nozzle exit from the outside, the zone of low pressure is created. 6 inlet ports (4) have been made in the body of the unit through which, due to depression, a suction of flushing fluid with the suspended rock-destruction particles (6) and particles of cuttings (7) from the annular space takes place. Then, the two-phased mixture passes through the mixing chamber, where smoothing of velocities occurs, enters the diffuser (5) and hits the material (8) resulting in destruction.

Fig. 2. The operation principle of the unit 1 – chamber of the flushing fluid input, 2 – nozzle, 3 – mixing chamber, 4 – inlet ports, 5 – diffuser, 6 – rock cutting particles, 7 – particles of cuttings, 8 – destructed material

Fig. 1. Jet unit of the jet-ejection bit: 1 – body of the unit, 2 – nozzle, 3 – headpiece with the diffuser

While using the unit the following factors influencing the rate of drilling were studied: the bit size (length of the mixing chamber, nozzle deameter, etc.), pressure developed (created) by the pump, ”Relit” particles size and their number, the distance from the bit to the well bottom, strength properties of the rock. To do this, a glass tube simulating the borehole wall and providing the possibility of visual observation of the process of drilling is glued to the prepared sample of rock. Then, the required quantity of "Relit" (tungsten carbide) fills in the well bottom, the distance from the bit to the well bottom is set. Upon expiration of the planned drilling time the feed range is measured and the drilling penetration rate (ROP) is calculated.

The first step was to determine the penetration rate dependence on the distance between the bit and the well bottom. Series of experiments were conducted on a ceramic tile with athe fixed length (97 mm) and diameter (18.4 mm) of the mixing chamber, nozzle diameter (2.4 mm), the pressure developed by the pump (9 atm), the inside diameter of the glass tube (55.5 mm) and weight (100 g), and "Relit" particle size (1.6-2 mm). The distance between the bit and the well bottom increased from 5 to 35 mm by steps of 5 mm. Three experiments were conducted with every value; then the average values ​​of mechanical speed were obtained (Fig. 3). The results showed that the distance between the bit and the well bottom affects the borehole diameter (Fig. 4).

Fig.3. Dependence of the drilling penetration rate on the distance from the bit to the well bottom

Fig.4. Dependence of the borehole diameter on the distance from the bit to the well bottom

Thereby, experiments provided, that with the increased distance from the bit to the well bottom, the ROP and the wellbore diameter values, at first, increase and then decrease. This is the evidence of the optimal distance existence (15 mm in this case), in which there is the most effective destruction. This result can be explained by the fact that when we have a small distance between the bit and the rock, the "Relit" particle velocity (tungsten carbide) after the intaking does not have time to catch up with the liquid jet speed. When the distance is large – the particles stall due to the hydraulic resistance.

Experiments to determine the dependence of the drilling penetration rate on the "Relit" mass were conducted on a set of ceramic tiles in the same values as in the previous series of experiments. The distance from the bit to the well bottom was kept to be 15 mm. Moreover, two series of experiments with different lengths of the mixing chamber were conducted. According to the results, penetration rate - mass "Relit" diagram was made (Fig. 5).

The diagrams, as in work [6], show, that ball-jet drilling has an optimal amount of particle mass, and the drilling penetration rate is maximum. When the amount of abrasive particles in the borehole cavity is less than optimal, the rock is destroyed by the insufficient number of hits, and when it is more than optimal amount, there occur lots of collisions between the bounced from and falling to the bottom particles resulting in the stall of the last ones. Besides, it was established that when we reduce the mixing chamber length, the drilling velocity increases considerably. It is the lower turbulization of the mixed flow that leads to the increase of the jet hitting range.

Fig. 5. Dependence of the drilling penetration rate on the «Relit» mass  

Further steps:

1. Improve the developed unit for the jet-bit-erosive drilling. There are some complexities of measuring the distance between the bit and the bottom, centering the bit in the glass tube, etc.

2. Ball-jet unit operation theory research, identification of the ball-jet drilling rock destruction mechanism. Basic analytical characteristics determination. These describe rock destruction with the ball hits.

3. Conduct experiments to identify drilling penetration rate dependence on the geometric sizes of the bit components, strength properties of rocks, types and properties of the fluids used, etc.

4. Development and testing of the bit design characteristics, which can create acoustic vibrations, more effective to rock destruction (ex. weak sudden expansion behind the nozzle, and the application of the variable cross-section nozzle, etc.)

References:

1. Сулакшин С.С. Разрушение горных пород при бурении скважин: учебное пособие для вузов. – Томск: Изд-во ТПУ, 2004. – 136с.

2. Технология бурения нефтяных и газовых скважин: учебник для вузов/А.Н. Попов, А.И. Спивак, Т.О. Акбулатов и др.; под общей ред. А.И. Спивака. – М.:ООО «Недро-Бизнесцентр», 2003. – 509с.

3. В.А. Бреннер, А.Б. Жабин, А.Е. Пушкарёв, М.М. Щеголевский. Гидроструйные технологии в промышленности. Гидромеханическое разрушение горных пород. – М.: Издательство академии горных наук, 2000. – 343 с.: ил.

4. Eckel I.Е., DеiIу F.H., Ledgerwооd L.W. Development and testing of jet рumр pellet impact drill bits // Transaction AIME. – Vol. 207. – 1956. – p. 135.

5. Уваков А.Б. Шароструйное бурение. – М.: Недра, 1969. – 207 с.

6. Заурбеков С.А. Повышение эффективности призабойных гидродинамических процессов при шароструйном бурении скважин: автореф. дис. на соискание ученой степени канд. техн. наук. – Алматы, 1995. – 18 с.

7. Столяров Р.В., Ковалёв А.В. Разработка гидромониторного долота эжекционного типа // Проблемы геологии и освоения недр: труды Тринадцатого международного симпозиума им. М.А. Усова. – Томск, 2009. – С. 476–477.

8. Столяров Р.В., Ковалёв А.В. Установка для абразивного бурения с применением долота гидромониторно-эжекционного типа // Проблемы геологии и освоения недр: труды Четырнадцатого международного симпозиума им. М.А. Усова. – Томск: Изд. ТПУ, 2009. – С. 520–521.

9. Алиев Ф.Р., Ковалёв А.В., Епихин А.В. Исследование работы гидромониторного долота эжекционного типа // Проблемы геологии и освоения недр: труды Шестнадцатого международного симпозиума им. М. А. Усова. – Томск: Изд. ТПУ, 2012. – С. 284–286.

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