One of the most widely used methods for creating production and exploration wells for water is rotary drilling. It is provided by the transmission of rotational movements from the surface rotor to the drill string.
Rotary drilling is characterized in that it lacks the axial force generated by the drive. During the process, the production (bottom hole) from the waste material is washed with water and special solutions. Consider the method in more detail.
History reference
Rotary drilling has been used for over one hundred and forty years. The technology of this method of punching wells was first used in the United States of America in the early eighties of the nineteenth century. Since then, it has not changed much, with the exception of minor innovations that have led to greater efficiency. The changes affected rock-cutting tools - they improved, new liquid media were created for washing the wells, and the strength of the parts of the mechanism was strengthened.
Rotary well drilling is a type of rotation drilling. The principle is that a tool for rock destruction, located inside the well, works 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 installation allows it to be used on private land to create water wells.
Drilling methods
Currently, water wells are drilled using rock cutting methods using special mechanisms. Upward soil can be supplied in two ways:
- Using mechanisms - a dry method.
- A stream of water under high pressure or by gravity - hydraulic.
In general, mechanical drilling is carried out in one of three ways:
- Rotary rotary drilling - the soil is drilled by rotational movements.
- Impact - the soil is destroyed by the impact of a drill.
- Vibratory - the soil is broken by high frequency vibrations.
The first method is the most used due to its simplicity, low cost and at the same time performance.
When does the method apply
Rotary drilling is used when semi-rocky and rocky soils are developed for the construction of 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 efficient operation, rotary drilling should be used if the 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 rock.
- There is data on the level of occurrence of the aquifer.
- There is good groundwater pressure.
- There is the possibility of constant delivery of flushing fluid.
In addition, it should be borne in mind that the conditions in the southern regions allow drilling operations to be carried out year-round, and in the northern areas the work is limited by the temperature indicators of the external environment at which the washing liquid freezes.
Well Drilling Equipment
Rotary drilling technology involves the use of special rigs - mounted on the basis of self-propelled vehicles or stationary. Both those and others should have the following components:
- Engine.
- Tower.
- Drive unit.
- Swivel - a system that feeds liquid into the face.
- Drill string.
- Rotor.
- Piston pump.
- Lifting mechanism, including block and crown block.
- Pressure line
- Liquid return and purification system containing hydrocyclones, gutter and vibrating screen.
Advantages and disadvantages of the method
The rotary well drilling method has several advantages over other methods. Among them, the following should be noted:
- It exceeds the rest in performance: five times - shock and ten - vibration method.
- It has a high speed of work.
- Through the use of a variety of removable bits, it can be used on soils of varying complexity.
- The installation has compact dimensions, therefore it can function in a limited space.
- Due to the possibility of location on the platform, the unit is quite mobile.
- It enables the drilling of deep wells and water intake from fractured limestone.
- The method has good qualities of opening a water carrier.
- Allows you to arrange wells up to two hundred centimeters in diameter.
Along with these advantages, rotary guided drilling has the following disadvantages:
- It is necessary to take into account the type of soil in order to choose the right bit.
- The presence of superhard rock particles in the path 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 the rotor installed at the moment.
- The need for constant availability of large amounts of flushing fluid.
Despite certain disadvantages, the advantages of this method are much greater.
The principle of operation of rotary plants
Rotary well drilling is performed by a special installation - a frame or trellised tower, mounted on the platform. All other systems are attached to it, allowing you to raise and lower the drill string in a profiled shape. Such a 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 transmission. By rotating, the rotor drives the bit, which destroys the soil layer with working edges in the well. The range of turns can be adjusted. The edges of the bit can be diamond, composite or carbide. Their shape may vary.
The developed soil layer by direct or reverse washing is displaced from the mine by gravity or under pressure using pumping units. After flushing the well , casing pipes are installed in it. By means of the swivel and hollow pipes of the drill string, flushing fluid enters the bit, eroding the soil under the bit. Through the gap between the pipes and the barrel, the fluid carries the soil out. On the surface, through special filters, the liquid is collected and cleaned so that it can again be put into operation using piston pumps.
Features of rotary well drilling technology
The drilling process is organized in such a way that due to leaching of the soil layer from the mine, the drill string goes deeper and deeper with each movement. Periodically, it must be increased by the addition of other pipes.
The drilling process is performed in steps:
- Having passed the first loose soil layers, the string is raised, and the casing is lowered into the shaft.
- The gap in a circle is filled with a cement solution.
- After the cement hardens, a bit with a smaller diameter is fed into the mine, and work continues on.
Several 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 formation and depth, the number and weight of pipes, the type of bit, the speed of its rotation and the material of the edges, the pressure of the flushing fluid are selected. The specifics are as follows:
- Light rock formations pass with maximum speed and maximum flushing.
- Rocky soils require a reduced frequency and reduced fluid pressure.
Hard ground impurities — boulders — in the path of the rotor, which may jam, or soils that actively absorb flushing, can interfere with work. The lack of water at the work site and the presence of a large clay layer also slows down the process. Clay, mixed with water, clogs the water channel and requires additional thorough washing.
Casing
After drilling a well, it is important to strengthen its walls. The soil is unreliable and may shift, which will negatively affect the face.
To prevent rock collapse, a casing is installed . It helps prevent soil from sprinkling and prevents water leakage. The first column is called a "conductor." It is mounted to cover unstable rocks. Installation takes place at a distance of no earlier than 30 meters and no later than 600 meters. For an oil well, the column is placed at a distance as close to the surface as possible.
Since rotary drilling is used for almost any type of soil, the workers are guided by geological conditions during the installation of the columns. Sometimes it is necessary to use several casing strings to strengthen the face.
The smallest of them falls deeper than the rest and is called operational. Perforation is made from below, it is through these openings that a mass of gas, water or oil will enter it.
The value of flushing fluid in drilling operations
A properly selected flushing method for rotary well drilling can significantly increase the efficiency of the process. In works of this type are used:
- Polymer solutions.
- Oil emulsions.
- Aerated solutions.
- Water.
Also widely used is the air purge method. If the 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, crumbled rocks, which is inevitable during drilling. Fluid trapped on the chisel cools it. Which extends tool life.
Rotary well drilling takes place in three stages:
- The destruction of terrestrial rocks using a bit.
- Running water to carry the destroyed rock. The process can be carried out both by reverse and direct washing, it all depends on the depth of the well, the amount of water used and the type of soil. In private households, the direct flushing method is popular.
- Strengthening the walls of a new well using casing pipes.
Rotary well drilling is a time-consuming process that requires many factors to be considered. Despite this, it is considered quite effective and is used in various conditions.