Rotary drilling: technology, principle of operation and features

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

One of the most widely used methods of creating production and exploration wells for water is rotary drilling. It is provided by the transfer of rotational movements from the surface rotor to the drill string.

Rotary drilling is different in that it has no axial force generated by the drive. During the process, the working (slaughter) is washed from rock waste with the help of water and special solutions. Consider the method in more detail.

Historical background

Rotary drilling has been used for over one hundred and forty years. The technology of this well drilling method was first used in the United States of America in the early eighties of the nineteenth century. Since that time, it has remained virtually unchanged, with the exception of minor innovations that have led to greater efficiency. The changes affected rock cutting tools - they were improved, new liquid media were created for flushing wells, and the strength of parts of the mechanism was increased.

Rotary drilling is one of the types of rotary drilling. The principle isthat the rock breaking tool, located inside the well, operates from the force transmitted to it by an electric motor or gas turbine equipment. This method is quite simple and effective. With its help, production oil and exploration wells are drilled. The compact size of the unit allows it to be used on private land to create water wells.

Drilling Methods

At present, drilling of wells for water is carried out by rock cutting methods using special mechanisms. Soil can be fed up in two ways:

• With the help of mechanisms - dry method.
• Jet of water under high pressure or gravity - hydraulic.

In general, mechanical drilling is carried out in one of three ways:

• Rotary rotary drilling - the soil is drilled with rotary movements.
• Impact - the soil is destroyed by the impact of the drill.
• Vibrating - the soil is broken by high frequency vibrations.

The first method is the most used due to its simplicity, low cost and performance at the same time.

When the method is applied

Rotary drilling is used when semi-rocky and rocky soils are being developed for drilling wells up to one hundred and fifty meters deep. For successful drilling of rocks, it is necessary to choose the right drilling tool - a chisel and weighted pipes. According to experts, for effective operation, rotary drilling should be used ifthe following conditions are met:

• The study of the hydrogeological section of the site was carried out in sufficient detail.
• It is known that the soil consists of rocks.
• There is data on the level of the aquifer.
• There is good underground water pressure.
• There is the possibility of constant delivery of flushing fluid.

In addition, it should be taken into account that the conditions of the southern regions allow drilling operations year-round, and in the northern regions, work is limited by the temperature of the external environment, at which the flushing fluid freezes.

Equipment for well drilling

Rotary drilling technology involves the use of special installations - mounted on the basis of self-propelled vehicles or stationary. Both of them must have the following components:

• Engine.
• Tower.
• Drive.
• Swivel - a system that supplies fluid to the bottomhole.
• Drill string.
• Rotor.
• Piston pump.
• Lifting mechanism including block and crown block.
• Pressure line
• A liquid return and purification system containing hydrocyclones, a chute and a vibrating screen.

Advantages and disadvantages of the method

The rotary drilling method has a number of advantages over other methods. Among them, the following should be noted:

• Exceeds the rest in terms of performance: five times the impact method and ten times the vibration method.
• Has a highspeed of work.
• Due to the use of a variety of removable chisels, it can be used on soils of varying complexity.
• The unit has a compact size, so it can operate in a limited space.
• Due to the possibility of location on the platform, the unit is quite mobile.
• Enables deep well drilling and water extraction from fractured limestone.
• The method has good water-bearing properties.
• Allows drilling wells up to two hundred centimeters in diameter.

Along with these advantages, rotary steerable drilling has the following disadvantages:

• Be sure to consider soil type to find the right chisel.
• The presence of super-hard rock particles in the way can be an obstacle requiring the use of more destructive mechanisms.
• Clay soil may interfere.
• A serious obstacle to drilling is frozen ground.
• Power depends on currently installed rotor.
• The need to always have a large amount of flushing fluid.

Despite certain disadvantages, this method has much more advantages.

The principle of operation of rotary units

Rotary drilling of wells is performed by a special installation - a frame or lattice tower, fixed on the platform. All other systems are attached to it, allowing you to raise and lower the profiled drill string. Suchthe column is assembled from several pipes connected by collapsible couplings.

The driving force is the car's electric motor or a separate generator, which transmits rotation from the column to the rotor through the drive shaft and gear train. Rotating, the rotor drives the chisel, which destroys the soil layer in the well with its working edges. The range of rotation can be adjusted. Bit edges can be diamond, composite or carbide. Their shape may vary.

The developed soil layer is displaced from the mine by direct or reverse washing by gravity or under pressure using pumping units. After flushing the well, casing pipes are installed in it. Through the swivel and hollow pipes of the drill string, flushing fluid is supplied to the bit, which erodes the soil under the bit. Through the gap between the pipes and the barrel, the liquid carries the soil out. On the surface, liquid is collected and cleaned through special filters so that it can be put back into operation using piston pumps.

Features of rotary drilling technology

The drilling process is organized in such a way that, due to the washing out of the soil layer from the mine, the drill string goes deeper with each movement. Periodically, it must be increased by adding other pipes.

The drilling process is performed in steps:

• After passing the first loose layers of soil, the column is raised, and the casing is lowered into the shaft.
• The gap is filled in a circle with cement mortar.
• Afterwhen the cement sets, a bit with a smaller diameter is fed into the shaft, and work continues on.

Several of these similar steps can be performed, and then a production pipe perforated at the end is lowered into the shaft. Depending on the quality of the soil layer and depth, the number and weight of pipes, the type of bit, its rotation speed and edge material, and the pressure of the flushing fluid are selected. The specifics are as follows:

• Light rock formations run at maximum speed and most flushing.
• Rocky soils require reduced frequency and reduced fluid pressure.

Soil hard inclusions - boulders - in the path of the rotor, which can jam, or soils that actively absorb washing can interfere with work. The process is also slowed down by the lack of water at the work site and the presence of a large clay layer. Clay, mixing with water, clogs the water channel and requires additional thorough washing.

Casing pipes

After drilling a well, it is important to strengthen its walls. The soil is unreliable and may shift, which will negatively affect the bottomhole.

To prevent the earth from collapsing, a casing string is installed. It helps to prevent soil from crumbling and prevents water seepage. The first column is called the "conductor". It is mounted to cover unstable rocks. Installation takes place at a distance not earlier than the mark of 30 meters and not later than 600 meters. For an oil well, the column is placed at a distance, maximumclose to the surface.

Because rotary drilling is used in almost any type of soil, during the installation of columns, workers are guided by geological conditions. Sometimes you have to use several casing strings to strengthen the bottomhole.

The smallest diameter of them sinks deeper than the rest and is called operational. Perforation is made from below, it is through these holes that the mass of gas, water or oil will flow into it.

The importance of drilling fluid in drilling operations

The right flushing method for rotary drilling can significantly increase the efficiency of the process. In works of this type apply:

• Polymer solutions.
• Oil emulsions.
• Aerated solutions.
• Water.

The air purge method is also widely used. If work is carried out in areas with low reservoir pressure, then workers use a special gas. Flushing helps to get rid of excess impurities and objects, crumbling rocks, which is inevitable in the drilling process. The liquid that gets on the bit cools it. Which extends tool life.

Rotary drilling takes place in three stages:

1. Destruction of earth rocks using a chisel.
2. Launching water to carry out the destroyed rock. The process can be carried out both by reverse and direct flushing, it all depends on the depth of the well, the volume of water used and the type of soil. Used in private householdspopular direct flushing method.
3. Strengthening the walls of a new well with casing pipes.

Rotary drilling is a labor-intensive process, during which many factors must be taken into account. Despite this, it is considered quite effective and is used in various conditions.