At present, the rack and pinion multi-functional drilling rig developed by TTS sense in Norway, American augers in the United States and Max Streicher in Germany has been able to meet the drilling demand of 3000-5000 m well depth. In practical application, it is mostly used for drilling operations of extended reach wells, horizontal wells and sidetracking horizontal wells.
1. Technical advantages of rack and pinion drilling machine
Rack and pinion drilling machine is especially suitable for shallow horizontal wells, extended reach wells and branch wells. Conventional rigs cannot actively apply any WOB. If the horizontal well is to be drilled, it is necessary to drill a deep vertical well before making a deviation, so as to use the gravity of the drill string to exert WOB on the bit, otherwise it will be difficult to run in and casing. In addition, due to the lack of enough WOB, the drilling length of horizontal section is also limited. The rack and pinion drilling machine can solve these problems by using its own thrust and tension. In June 2007, HWD (horizontal well drivers) Company of the United States used vr300 rack and pinion drilling machine of American augers company to drill 10 horizontal wells in Indiana, with a vertical depth of 122-213 m and a horizontal section length of 1219-1646 m, with good results.
2. Market demand of rack and pinion drilling machine
The reserves of medium and shallow oil and gas resources distributed within 3500 m in the world are amazing [4-6]. 41.5% of the oil and gas produced in the United States comes from the shallow layer within 915 m [5]. 80% of China’s recoverable gas resources are distributed in the shallow layer within 2000 m and in the middle and deep layer of 2000-3500 m, while the deep layer of 3500-4500 m and the ultra deep layer of more than 4500 m are less [7-8], and most of China’s existing oil and gas fields are in the middle and late stage of development, which requires sidetracking horizontal wells and other operations to tap the potential of old wells.
The remarkable economic and social benefits brought by the development of oil and gas resources in horizontal wells are obvious to all, which shows that the application prospect of rack and pinion multi-function drilling machine is very broad.
3. Suggestions for domestic development of rack and pinion drilling machine
The core technology of rack and pinion drilling machine is its lifting system, which mainly involves rack and pinion technology, AC frequency conversion electric technology and hydraulic technology. Rack and pinion technology refers to rack technology and gear technology installed on derrick to provide thrust and tension. Both AC frequency conversion electric technology and hydraulic technology provide power source for rack or gear movement.
The advantages of the electric scheme are large short-time overload capacity, convenient control, simple maintenance, and large volume. The average total efficiency of electric scheme is about 85% ~ 90%, which is 15% ~ 20% higher than that of hydraulic scheme [13]. The advantage of the hydraulic scheme is that it has the characteristics of compact structure and large torque under the equivalent condition. The disadvantage is that it is sensitive to the temperature change and needs relatively heavy hydraulic power unit.
In view of the advantages of AC variable frequency electric technology more prominent than hydraulic technology, it is suggested to carry out the development of AC variable frequency electric drive rack and pinion drilling machine in China.
4 Conclusion
(1) Compared with the traditional oil drilling rig, the rack and pinion drilling rig has the advantages of high transmission efficiency, simple structure, convenient transportation, energy saving and environmental protection, low operation cost and high degree of automation, which can better solve the problem of drilling pressure in the process of drilling horizontal well and extended reach well, especially suitable for the drilling operation of shallow oil and gas reservoir development in horizontal well, and has a broad application prospect.
(2) At present, the main enterprises producing rack and pinion rigs in the world are TTS sense company in Norway, American augers company in the United States and Max Streicher company in Germany. The hoisting system design of three companies has different characteristics, among which the vdd400 drilling rig of Max Streicher company has the largest thrust, reaching 880kn.
(3) In view of the market demand and the existing technology, it is suggested to develop the AC variable frequency electric drive rack and pinion drilling rig in China.