Vladimir SUSHKO, Novinka Unitary Enterprise

 

The radial drilling technology was developed by the Rad Tech International Inc., an American company established by Henk Jelsma, its permanent head and the technology patent holder. First introduced in the New World, the radial drilling technology acquired wide recognition in the USA and Colombia and later on found its application in Canada, Bolivia, Argentina, Chile and the Middle East.

 

The leader in the radial drilling services market is the Radial Drilling Services Inc. (RDS), international service company with its headquarters in Houston.

 

This breakthrough technology first appeared in Russia in 2002. Its application was initiated by JSC Tatneft which has always been eager for innovations. The pilot tests being successful, the RVPlast joint venture was incorporated in Tatarstan in 2005. JSC Lukoil was next to turn to the promising technology. For the moment, most of the major Russian oil and gas production companies are willing to put the technology to practice use. The radial drilling technology demonstrated impressive performance in Kazakhstan. Belorusneft has put it to test, too.

 

What is the root principle of the technology? According to its inventor, Henk Jelsma, “We have created the radial drilling system to stimulate vertical wellbore production. Initially, the technology was intended for marginal wells whose flow rate becomes extremely low by the end of well life, or, to be exact, for the cases when the vertical wellbore is completely blocked within the range of potentially productive formation. Generally, companies tend to abandon such depleted wells and find new oil fields trying to avoid additional costs”.

 

“Since originally this system was positioned as intended for low budgets, we didn’t mean to cooperate with Gasprom-scale companies, our main contacts being small businesses which could apply our technology as an alternative to the costly horizontal drilling. However, the technology having been further developed and tested in the USA, we may now use it in the standard procedure of well completion for the purposes of inflow stimulation, directed acid treatment, and chemical treatment.”

 

The radial drilling technology is applied for:

If slightly modified, the technology may be used to rehabilitate the injection wells with collapsed (displaced) casing.

 

In general, this technology is aimed at extending and improving drainage areas in

productive formations. Other applications of radial drilling include creation of specifically directed injection channels and exploration activities.

 

The technology is also made use of in heavy oil fields. As compared to the conventional methods, radial wellbores used in the course of huff-andpuff procedure are instrumental in warming up a significantly larger zone.

 

It is of vital importance to provide a balanced decision as to the selection of candidate wells. Experts are unanimous about the necessity of making projects, as the wrong choice may cause the results not being up to expectations. JSC Lukoil record has proved that the efficiency of radial drilling is the highest in carbonate reservoirs. As for terrigenous reservoirs, the results leave much to be desired because of clay swelling in soft water and causing obstruction of wellbores of 25–30 mm in diameter. This problem can be solved, though only to an extent, with the help of anti-swelling polymeric drilling mud agents.

 

It should also be noted that it is common to choose wells for radial drilling among those unresponsive to other methods.

 

After formation drilling, production rates increase averaged at 1.5–2 tons for JSC Tatneft, and about 8 tons for JSC Lukoil. Still, it is far from being maximum limit. Some wells produced increase up to 40 tons per day, so, “standard” production output may be 15–20 tons higher.

 

The operating principle of the technology is based upon hydraulic fracture treatment of hard rock. The overall picture is the following. Before radial drilling the oil-well remediation crew carries out well conditioning: retrieves the downhole equipment

and calipers the production casing string.

 

The guiding gooseneck (for the wells up to 2,500 m deep) or an injector with a gooseneck on it (for the wells more than 2,500 m deep) is rigged up on site. It should be noted that in Russia injector equipped units are in more demand, as practically all the wells in Western Siberia – major oil and gas production region of the country – have their operating depth of 3,000 m and more.

 

A deflector shoe with a special passage for instruments (milling tool) and a hose with jet nozzle goes all the length of the drilling zone into the well cleaned of paraffin and other deposits.

 

Then a window cutting unit is assembled. The tool for window cutting is driven by a screw downhole motor which operates at the velocity of at least 100 rotations per second and runs in the hole with the coiled tubing. After that the coiled tubing is used to run down in the hole a formation drilling assembly consisting of a jet (water injection) nozzle and high pressure hose armored with Kevlar – a special flexible and durable material. The high-pressure pump drives fluid to the jet nozzle, and its jets break the rock and by means of jet propulsion facilitate the assembly movement along the formation. The bore size depends on the tubing penetration rate and averages at 25–50 mm in diameter.

 

The penetration procedure is controlled from outside basing on the coiled tubing tension (in shallow wells) or on the tubing weight sensor reading (if injector is operating). Time of making one hole of up to 100 m long is about 20–30 minutes. The technology does not limit the number of radial bores drilled from one well. They can be made either at one level, or at several levels.

 

The operations above completed, the tubing with deflector shoe is retrieved, the production assembly goes down the well and the well is put in production. The whole process takes up from two to four days, the well shutdown period being two to

four working days respectively.

 

The Novinka Unitary Enterprise (the FID Group) has created, produced and put through field tests a system for coiled tubing radial drilling.

 

COMPONENTS AND SPECIFICATIONS OF A SPECIAL COILED TUBING UNIT FOR RADIAL DRILLING

The unit comprises a semitrailer, a control cabin, a tubing spool assembly, a hydraulic drive for the tubing spool assembly, a guide arch, blowout preventing equipment, a pumping unit, a working tank, a control and recording system, a steering assembly, a window cutting assembly, an assembly for creation of filtration channel in the productive reservoir.