How is it possible to value the quality of rods?
1. Some words from the history of drill rods designing for the rotary drilling
First time, in the last century, drill rods for rotary drilling were made of low carbon steel and connected to each other in column with the help of shallow thread which withstood the multiple screwing and unscrewing badly and required much time for the performance these operations in jostle of the drill string.
In 1910, tool joints with the tapered buttress
thread of the big step were created, which were joined with a rod through a shallow tapered threads triangular profile.
In 1914 the more durable rods made of steel with high content of carbon appeared, and in 1919 – rods with upset inside ends, that it compensated the reduction of the wall thickness which appeared during the cutting of the thread (a prototype of oil drill rods according to 631-75 and exploration drill rods GOST 7909-56). In the same year, the volumetric thermal treatment of tool joints (increasing) was developed owing to which the resource of the tool joint’s thread was increased.
However it was not enough for exploration
tool joints that later as it was found out in the 60-s, owing to the introduction tube turn - because of the wear and jamming of threads the average resource of tool joints did not exceed 200 cycles of screwing-unscrewing or 800-1200 hours of clean drilling. Here it had to apply the more effective measures on hardening - its superficial quenching with the heating of High Frequency Currents (SS 7918-75).
Despite of upset ends of rods the weakest place the rod’s thread, there mainly happened breakages of the drill column. A lot of efforts were made for its hardening: blunt profile, rollers’ running, the superficial quenching, the formation of the thread with the help of knurl and etc.
Finally, “SKB Geotechnika” found out the
satisfactory solution through the introduction into the tube thread T-50 the tight butt, and on this
basis the company designed Heavy Weighted Rods HWR – P – 73.
However, as the experience of these rods
exploitation showed that the instability of negative allowance lead to disclosing of thread’s butts and, as a consequence, it lead to frequent breakages of threads including a large number of them in the column.
Simultaneously, the research on the abolition of the rod’s thread was carried out by developers choosing the way of manufacturing tool joint’s connection with the rod. The first such connection designed in 1931 foresaw the thick walled upset on both ends of the rod. However such design had the raw of significant defects that’s why it was used extremely seldom. To these defects regard the following:
1) It is necessary to manufacture the entire tube of expensive alloyed steel;
2) Because of its large dimensions of rods complicated or exclude the possibility of chemical thermal hardening and other ways threads’ hardening, it is complicated the metrological control of threads’ parameters;
3) Disadvantaged macrostructure reduces fatigue resistance of the thread because of upset of rods ends.
Therefore, the more rational design is proved that one in which to ends of the cheap carbon steel are welded tool joint’s details of alloyed steel, durable and enough plastic steel.
This design has been widely applied world wide. In drilling on oil drill rods are "Drill rods with weld-on tool joints." Technical Conditions (GOST R 50278-92) these drill rods are analogical to drill rods of API standard (USA). Here 7 groups of durability are foreseen: D, E, L, M, R, T and U with the limit of durability from 655 up to 1241 Mega Paskal. However the columns of group of durability D and E have got the practical application, the extreme depth of carry is 4750 and 6250 m. For columns of
rods of Group of Durability M the carry can be up to 11200 m.
The using of drill rods of group of durability M is inadvisable because of two reasons:
1) the limit of endurance reduces because of high values of the active voltage concentration coefficient and the coefficient, which characterizes the scaled factor that can lead to a fatigue breakage of rods along the body of the rod;
2) unworthy the cost of the deficit steel increases.
For the exploration drilling according to the standard “Steel Universal Drill Rods. General Technical conditions”(SS R 51510-99) it were designed drill rods with weld-on tool joints of 4 types of durability (TC 41-01-676-95):
• N - normalized (group of durability D and K);
• I - improved (group of durability ?);
• NQ – normalized with the surface quenching;
• IQ – improved with the surface quenching
As the 10 year experience of exploitation showed in different regions of Russia, drill rods of types N and NQ according to durability and failure satisfy themselves practically with everything including the complex geological technical conditions of drilling.
Drill rods of types I and IQ which are intended for drilling in enough complex conditions (cavernous, labile, very abrasive solids, in intensive deviation of the well bore and etc.) they are at the stage of development.
Design of drill rods of group of durability above M aren’t foreseen according to the above-mentioned reasons.
2. Make the right choice during the acquisition of drill rods!
Despite the fact that now officially the new standard for the modern exploration drill rods (SS R 51510-99) acts but more often different variants of non-standard drill rods or drill rods of old standards began to appear at the market, the action of these rods is terminated in Russia. This fact significantly hinders the consumer to make the right choice, because of in the most cases in advertising materials the indicators of strength, durability, trouble of rods, their economical efficiency during drilling process is absent.
To make the right choice, it is necessary to
use the most objective three criteria of efficiency:
1) with the expense of drill rods per the unit of drilling volume (pieces per 1 well of a given depth; pieces per 1 meter of the well and etc.);
2) trouble of rods;
3) easy using in the process of their exploitation.
To help the consumer, we offer the more simple method of such choice in the example of the evaluation of four variants of drill rods, which are available today on the Russian market of drill rods (see table 1).
We take into account the general for all variants of comparative rods the following geological technical conditions of drilling:
• the depth of the well - 500 m;
• the length of the rod with the tool joint – 4.7 m;
• the well borer with smoothly adjustable drive power 30 kilowatt;
• the diameter of the drill crown – 76 mm;
• the ratio of the well’s bore – 1.30;
• the average axial load on the working face of the well - 1.25 kN (kiloNewton);
• The twisting torque (n) is calculated with the strength’s resource V = 1.3 according to the fatigue resistance on reversed bending.
• The mechanical drill speed (V) is defined by dependence Vm = 103 5.3n (n – rotating speed, rev/min);
Besides we take into account that;
• the column’s resource is equal to the double resource of the rod because they start to work gradually, and they don’t start to work at the same time;
• the general amount of rods in the
column is 106 pieces (without taking into account of the possible changes);
Drilling volume during the column’s operation is equal to the resource and the last one is divided into the mechanical speed;
• The number of exhausted tool joints is against the resource of the rod to the resource of the tool joint multiplied to the number of rods in the column (106) divided to the resource of the column and multiplied to 500.
• The results (see table 17) give enough clear imagination about the quality of compared rods. To make the final choice it is enough to calculate the expense of rods in value terms, using the seller's price list and to take into account what variant of rods provides the maximum drilling speed.
It should also be taken into account other
2 criteria which are not included in this calculation, but they are well known from the experience of the exploitation:
• The trouble of compared columns depends not only on the durability of
threading connections on alternating load (Mextreme), but threads’ resistance to wear, and especially jamming, which are inevitable in the hardness of the material less than 48 HRC. In rods of version I and II the jamming of the rod’s thread conduct to the loss of rod and the tool joint’s details, and in version III the jamming of the rod’s thread entails the loss of two rods, and two performed at the same time with them two tool joints. In the variant IV (the drill rod SUDR) the possibility of jamming of carbonitrated threads is excepted because the thread’s hardness in this variant is more than 50 HRC.
• Drill rods of above the group of durability
M are less plastic and very sensitive to impact loads. They require more careful treatment as transportation and unloading as in the process of jostle of the drill string. Impact loads here can lead to brittle fracture and cracks which will invariably show themselves in the process of drilling and the more dangerous during jostle operations
Lachinjan Leonid
Honoured person in the Science of the Russian Federation.
Doctor of the Technical Sciences, Professor
