Electrodrilling: Past Experience and Present Opportunities
Authors: Abyzbayev B.I. , Baibakov N.K. , Baidyuk B.V. , Gelfgat Ya. A. , Gelfgat M. Ya 
Published: December 2007

This paper, for the first time in western oil industry practice. presents prehistory. Russian experience and present outlook of electrodrilling technology. Presented results obtained during drilling of wells of different types have provided for the basis of electrodrilling comparison with existing drilling methods. Two natures of electrodrill system, i.e. downhole motor and bottom hole information transmitter, are described. Big field experience indirectional, horizontal, multilateral and deep drilling with heavy mud, foam and air proves high efficiency of electrodrilling in very complicated well conditions. Numerous research wells drilled with electro-motors allow to consider electrodrilling as universal method. It combines advantages of rotary and hydraulic down-hole motors drilling. Great prospects of electrodrills application with coiled tubing techniques are outlined as well.

Introduction

Development of an electric downhole motor is based on the idea of using more effective electric energy. This kind of energy has the following advantages:it is cheap and convenient for long distance transmission;it is easily transformed into other kinds of energy with high efficiency. permitting the use of automatic technologies and remote control;it permits to keep constant high power through compensating power losses in transmission lines by increasing voltage.

All the above allows to develop highly effective downhole motors for driving drilling bits and to automate well drilling process.

This report deals with development of electrodrilling, achieved results and prospects of electrodrilling application in modern drilling systems.

1. Prehistory

During the last 100 years experts from USA, Germany. France, Austria-Hungary. Romania and Russia have tried to develop drilling machines with electric motors. The first efficient electric downhole motor for deep drilling was developed in the USSR in 1937–1940. Aspirations for the development were driven by considerable advantages of the electric motor:power transmitted to the bit was high. constant and independent from fluid flow conditions;bit performance and rock destruction at the well bottom were controlled from the surface;information on penetrated rock properties was interpreted through bit performance.

Naturally, these advantages were accompanied by additional technical problems related to directing two parallel flows of energy to the bottom for bit rotation and bottom-hole cleaning.

The first electrodrill consisted of a 3-phase 4-pole motor with a capacity of 70 kW, a planetary gear which reduced rotation sped from 1,450 to 363 rpm and a spindle connecting the gear with a bit. Electrodrill diameter and length were 324 mm and 8.5 m respectively. Electrodrill housing was filled with oil under pressure to protect the mechanism from environment. The oil level was kept by a compensator. Drilling mud was pumped to the bit through an annular clearance between electrodrill case and the motor and mechanism housing. Current supply was effected through coaxial sections of a three-strand cable placed into drill pipes. The cable sections were connected with each other by sleeves and pins when making up drill pipe joints.

At the same time an electro-differential bit feed regulator was developed.

In 1940 in the village of Kala near Baku the first well in the world was drilled with the use of the described system. Well depth was 1,500 m. All parts of the system passed tests. Based on the tests results, the following conclusions were made:Electrodrill is able to operate successfully in aggressive liquid medium under high hydrostatic pressure and dynamic load.Current supply system is based on using discrete power cable placed into drill pipes.

P. 573^