№ 10 (October 2006)
How Past Lessons Learned Can Help Drillers Today and Tomorrow
After nationalization of the oil industry from 1922 to 1941, engineers and researchers consistently developed reliable designs of hydraulic and electric downhole motors.
By Yakov Gelfgat, Mikhail Gelfgat
Before the war started, a company named the Experimental Turbodrilling Bureau was founded in the Baku region. When the war began this company pioneered turbodrilling to drill exploratory wells and production wells at a large oil field in the Perm region. Yet, the real breakthrough in drilling took place in 1943, when turbodrilling technology was used for directional single and cluster wells.
Quite soon, vertical and directional turbodrilling as well as cluster well drilling became widely used in commercial drilling applications for oil and gas throughout the country. By the late 1950s, 80 percent of the wells in the Soviet Union were drilled with turbine drilling technology.
The rapid growth of directional and cluster well drilling activity confirmed the advantages of downhole motor drilling technology in most of the oil and gas producing regions. From the second half of the 1960s until today, practically all Siberian oil fields were developed by cluster well drilling using hydraulic downhole motors. This was the key factor for the tremendous growth of the drilling and oil production volumes in the FSU during the next decades.
The advantages of the widely used downhole motor technology were so obvious that the technology itself managed to survive through another strong rotary drilling campaign. This campaign was triggered by the introduction in the US of the more durable three-cone TCI bit design with sealed bearings. In 1979 and 1980, VNIIBT conducted a special study to compare the results of turbodrilling and rotary drilling using the sealed bearing bit. The study convincingly proved the validity of the fact that when TMD is less then 2,500 m, the ROP becomes the main factor in improving the drilling efficiency.
Electrodrilling Technology Enhances the Progress
In 1941, Russian engineers built the first efficiently working electrodrill that was used for drilling wells with TDs of 1,500 meters. A few advantages of electrodrill application are listed below:
• the constant weight on bit while drilling, regardless of the parameters of drilling mud circulation;
• the possibility to monitor the bit performance and condition from the surface as well as to control the rock destruction process;
• the possibility of obtaining information about the properties of the drilled rock by analyzing the bit performance.
At large, the electrodrilling system was developed between 1952 and 1963, when electrodrilling became widely used in Ukraine, in Kuibyshev (now Samara) region, and in Turkmenia. Certain additional work was required to make substantial improvement in the electrodrilling system components, like cable connections and control unit, but most important, to identify the efficient areas of application where electrodrills would have a significant advantage compared to hydraulic downhole motors.
Within the period of 1963-1970, VNIIBT in cooperation with the Special Design and Technological Bureau based in Kharkov, Ukraine, developed an improved design of 127-290 mm OD electrodrills, with gear-reduction unit capable of reducing rotational speeds to 70 rpm, and a borehole deflecting tool. The primary achievement was the development and implementation of the world’s first successfully operating cable telemetry system. The system used the power cable to transmit signals to the surface, which allowed receive of real-time information about the borehole path parameters, such as the direction and inclination, as well as the deflector position. Operation of the new system promoted the expansion of electrodrilling method for directional and horizontal wells construction.
Electrodrills successfully drilled wells to depths in excess of 5,000 meters with complicated geological conditions that necessitated the use of heavy mud. Utilization of electrodrills when drilling with foam, air, gas, or aerated mud also indicated that, in many cases, they were unrivaled. Improvements in electrodrill technology resulted in increased volumes up to 600,000-1,000,000 meters per year (Fig. 1b).
In the last five years, some of major oil and service companies showed their interest in electrodrilling techniques. The reasons behind this interest are the bottomhole-to-surface communication, the electrodrills power, and possibilities to use electrodrill with small diameter coiled tubing. The work on the new generation electrodrill with a new type of electric motor was resumed in Russia but due to limited funding, no substantial results were achieved yet.
The dominating position of downhole motor technology radically influenced the development of oil producing industry in the FSU and encouraged a large number of new trends in development of drilling methods. Among those are horizontal and multilateral borehole drilling; horizontal boreholes sidetracking through a cased hole; drilling 394-1,000 mm diameter upper intervals of deep wells using the rotary-turbodrill system (RTB) and others.
To pursue the experience gained during VNIIBT work and during scientific drilling, for the last 15 years the Aquatic Company has been developing two technologies that deserve special mention here.
Drill Pipes Become Lighter When Using Aluminium
The first research work and experiments with aluminum drill pipes (ADP), started in the second half of 1950s and gave positive results. During the following years, ADP was widely used, especially in drilling directional wells combined with both hydraulic and electrical motors. ADP accounted for 60 percent of the total drill pipe consumption. Wide use of ADP enabled a substantial reduction of loads applied to rig hoisting equipment, reduced trip time, lowered hydraulic losses in the borehole, as well as lower transportation costs. ADP was successfully used in rotary drilling as well. The program of drilling scientific superdeep boreholes encourages development of stronger and more reliable ADP able to transmit higher tension and torque. Pipes marked LAIDP were successfully used when drilling Kola SG-3, Urals SG-4, Krivoy Rog SG-8 and other scientific wells in the 1980s.
Last six years provided significant growth of LAIDP demand in Russia. This was due to several reasons. Firstly, field development required deeper wells with significant horizontal displacement. Secondly, most of the drilling rigs in service have hook load capacity 75 and 125 tons. Besides, the Russian drilling industry gained significant experience in using aluminum drillpipes, especially in West Siberia.