Core Well Drilling: Technology and Work Nuances

Nikolay Fedorenko
Checked by a specialist: Nikolay Fedorenko
Author: Alesia Markova
Last update: August 2019

One of the most productive and economical methods of forming mine workings is core drilling. It is used in field exploration and engineering geology. In addition, this is the easiest and fastest way to gain access to groundwater for the organization of water supply.

You will learn all about the specifics of core drilling, the tool required for its implementation and application features from our article.

Scope of core drilling

Core drilling is a method that allows with the greatest accuracy to determine the depth of the roof and the bottom of the soil layers, as well as the depth mark of the groundwater mirror.

Core drilling technology is widely used in the following industries:

  • Water supply in industrial and private sphere. Drilling wells for private water supply, organizing water intake of entire villages or city blocks is effectively performed by core drilling due to the fact that the drill easily penetrates to great depths. A core projectile is capable of raising almost any destroyed rock except for water-saturated and loose incoherent soils (sand, gravel, pebbles);
  • Exploration in the mining industry. When the rock passes, a point impact on the soil occurs along the radius of rotation. In other words, a shell, structurally resembling a pipe, drills a solid rock mass without disturbing its structure and condition.
  • Building. Carrying out engineering and geological research to study the physical and mechanical properties of soils, the state of rocks. Column technology provides an opportunity to accurately determine the water level and to take water samples to study their aggressiveness with respect to concrete.

During core drilling, a core is extracted - a column of soil or adjacent soil layers. The core is characterized by an integral natural structure, which provides a comprehensive analysis of the studied rock. Drilling with a core pipe allows to determine the depth of the rock with the highest accuracy for the purpose of study.

Core drill
Core drilling ensures the integrity of the extracted core, which contributes to the qualitative study of the rock. At the same time, the highest quality cleaning of the face from the destroyed rock is performed.

The use of core drill in construction greatly facilitates and accelerates processes. A pile is easily hammered into the hole prepared by a core drill or a ready-made reinforced concrete structure is mounted. Core drilling allows you to create cylindrical holes in brick and concrete structures.

Work technology and equipment

Two methods of using a core drill are known: work with supplying fluid to the face or to the dry, that is, without drilling mud.

Drilling without the use of drilling fluid is used if incoherent soils are saturated with natural moisture in a quantity sufficient for penetration and extraction. Water is also not fed into the working shaft when passing through fluid-plastic, soft-plastic and stiff-plastic loam / clay, hard and plastic sandy loam.

The liquid is used without fail when drilling rocky and semi-rocky rocks. In the absence of water in this case, the recess is much slower. In addition, the likelihood of premature failure of the crown increases significantly, and therefore dry drilling is considered more costly.

Flushing Core Drilling Scheme
The technology of core drilling with flushing allows not only to extend the service of working equipment, but also the fastest and least time-consuming way to free the face from the destroyed rock

When drilling with drilling fluid, the rate of deepening increases significantly. Most often, this method is used when drilling wells of significant depth. This allows you to perform work in the shortest possible time with minimal risk of crown damage.

Still water under high pressure is supplied to the bottom during the development of the well in loose, incoherent soils, if coring is not a task. In this case, with a stream of water they simply wash the face, freeing the working shaft from the destroyed soil.

The principle of column technique

The core element in core drilling is a destructive cutting part mounted on the bottom of the core pipe. They call her a crown. For rock sinking, special crowns equipped with diamond tools are used.

Core drill bits
Crowns are cutting interchangeable elements that are screwed to the bottom edge of the core tube. In the process of drilling they have to be changed several times

It is the diamond crown that ensures the almost unimpeded passage of the drill to a great depth during the passage of water intake workings to limestone. That is, when developing wells buried in bedrock, in the fractures of which as a result of centuries-old condensation, the reserves of the purest underground water were formed.

Drill bit thread
Drill bits are changed in the simplest way - they remove the worn-out part and screw a new crown onto the core pipe

The rock is cut with a crown rotating at high speeds. The speed of rotation of the drill can be adjusted depending on the density of the developed soil. The crown “cuts out” the soil only along the edge of a peculiar cylinder, the central part of which is pressed into the core tube.

To extract the core, the drill is raised to the surface. The soil captured by him is literally blown out of the core drill with a stream of air supplied to the upper part of the pipe. The blowing process is accelerated by tapping the shell with a sledgehammer.

Core extraction from core pipe
During core drilling, a drilled cone-shaped rock segment is pushed into the core pipe. To extract it, the core shell is pulled out of the barrel by disassembling the drill string. The core is blown and pounded out of the pipe

Column drills during the passage of strong rocks have greater productivity than matrix and cone bits. This is due to the high speed of rotation of the drill, which reduces the degree of applied effort on development.

In addition, the chisels completely destroy the rock that will need to be “scooped out” by the bailer or pump water with a head to flush the face. In fact, you will have to go through the same segment twice, or even three times: first destroy, then clear. Column technology allows you to go through and clear the face in one go.

Machine tools and drilling rigs

The choice of a machine or drilling rig is determined by the purpose of the well and its diameter. The popularity of the core drilling method determines the production of drilling rigs and machine tools around the world. Heavy tractors, trucks and all-terrain vehicles are suitable for installations designed for exploratory drilling.

Crawler Drilling Rig
The use of heavy tracked tractors allows for core drilling in areas with impassability, surface waterlogging, and unstable terrain.

Most often, drilling equipment is mounted on classic MAZ, KAMAZ, and Ural automobiles. However, there are mounting options for lighter equipment, which is used for drilling water wells in private construction.

At manual rotary drilling the core pipe is replaced by its historical predecessor - the glass. This shell is a shortened version of the core tube with a pointed edge on the sole. A glass is manually or using a motor-drill, twisted into the ground and all that is piled into it is removed to the surface.

Motoborer for mechanization of manual drilling
For the mechanization of manual drilling of shallow wells and the formation of holes for the installation of fences and power transmission towers, gasoline and electric motors are used. They report rotational movements to the auger or core tube

Equipment for sinking and arrangement of wells

In the implementation of core drilling, equipment is needed that allows you to work in depth, to develop and extract a wide variety of types of rocks. During the work, a periodic rise to the surface of the material destroyed by the projectile should be provided.

Standard Drill Tool Set

For high-quality performance of work requires:

  • Column shells. They are used both for horizontal drilling and for drilling vertical workings. Using standard core pipes, drilling is possible at an angle of up to 45 degrees. Thin-walled core shells can only be used for horizontal trenchless drilling when laying communications.
  • Crowns. It is a rock-destroying tool that a core tube is equipped to facilitate core cutting in rock. For drilling sedimentary cohesive and incoherent soils, brass crowns are used. For sinking rocks, forming holes in concrete, asphalt, a brick wall, carbide crowns with diamond cutters are produced.
  • Steel casing. They are necessary for casing the production - the formation of the wellbore, produced simultaneously with its deepening. Their diameter is equal to the diameter of the well. The casing for water intake is selected in advance, focusing on the diameter of the core pipe and pump, which is planned to be operated in the well.
  • Rods. These are narrow pipes twisted together. Used to build the drill string. Simply put, they are alternately screwed to the top of the core tube so that it can transmit rotational motion at a depth exceeding the height of the projectile.The height of the core pipe + the height of the string of drill rods = depth of production.
  • Sub Necessary to ensure the joining of threaded joints of varying diameters that are present on the drill rods, rotatorsflushing oil seals and other accessories.
  • Flushing plugs and seals. With their help, the rise to the surface of the destroyed soil is provided, if there is no need for the selection of a whole core. In this case, water is supplied to the face, washing out the destroyed soil under pressure on the day surface.
  • Chisels. They are used to deepen the borehole in the most difficult places for the passage of core drill. When using a bit, sometimes they switch from rotary drilling to shock-rope drilling.

The presented tool is a standard set for drilling using core technology. In some cases, depending on the complexity of the development, additional tools and equipment may be required.

Set of rods for building core drill
When deepening the excavation, a string of drill rods is sequentially screwed to the top of the core pipe. To extract the core projectile to the surface, the rod after the rod is untwisted

Core design

Constructional feature shell during core drilling, it is due to the maximum preservation of core integrity and consists in an annular arrangement around the free passage. One of the most important characteristics is the coefficient core sampling. It is defined as the ratio of core diameter to the outer diameter of the tool.

The core drilling tool is standardized, it differs mainly only in diameter. According to the design features, core pipes are classified into single and double. Single shells designed to work in normal geological conditions are great for developing water wells.

A double tool with a non-rotating inner pipe is used only in geological exploration. It is needed to extract rock samples that are easily destroyed under the influence of a variety of factors. It allows you to take a sample in natural composition, with a natural percentage of minerals and waste rock.

Single core pipe
In sampling for engineering-geological research, in geological exploration and drilling of holes for the installation of power transmission line supports, a single core pipe is used

All core pipes are designed for the use of purging, supplying drilling mud to the bottom and flushing the well. Their top is equipped with a technological hole through which water or a stream of air is injected.

Specificity of the cutting part of the projectile

Any crown is presented in the form of a ring with a thread located on top, necessary for screwing to the core tube, and cutters located on the lower end. Cutters are cast or welded to this cutting metal part.

When coring, use the following crowns:

  • Carbide - small incisorsribbed.
  • Diamond - Impregnated and small diamond.

Carbide cutting elements are designed for drilling “soft” soils. With their help, all types of clay rocks of any consistency, semi-rock, low-moisture and moist sands of dense composition and medium density are drilled. To drive through sandstones and marls, crowns with tungsten-cobalt incisors are used.

Small incisors crowns are intended for drilling of medium hardness of small rocks abrasiveness. They are equipped with octagonal or square cutters. When the incisors are located at different heights, stepwise slaughter is also achieved, the advantages of which were described above.

Core drill ribbed drill bit
Using ribbed crowns improves the circulation of flushing fluid by expanding the diameter of the borehole

Ribbed core bits designed for medium hard rock drilling abrasiveness. Cutters of such crowns consist of steel cylindrical or prismatic staff with carbide insert. In this case, even in the case of wear of the crown does not decrease the efficiency of its work.

Crowns with diamond tools are designed for drilling rock and semi-rock of high abrasiveness.

Drill bit with technical diamonds
To increase strength and increase abrasive properties, industrial diamonds are pressed into its cast mass during the production process. Recently, natural crystals are often replaced by artificially grown

The number of ribs is determined by the design of the crown and its diameter - they can be from three to six. Acceleration of the process of rock destruction can be achieved by moving up the ribs relative to the end face of the crown. Thus, a stepped bottom is ensured and the passage of the flushing fluid is facilitated.

Wellbore casing tubes

Both core and casing steel pipes are produced in accordance with GOST 51682-2000. In exploration and engineering geology, they are used to prevent the collapse of the soil at the bottom, which would not allow us to understand at what depth one geological layer is replaced by another.

AT arrangement of water intake openings casing pipes form the walls of the well. In the casing assembled from them, another operational pipe string is immersed. Now it is most often assembled from plastic. The production casing is equipped with a filter for holding sand grains and fine gravel during pumping.

The most common are casing pipes with nipple joints. At the same time, pipes have an internal thread on one side, and an external thread on the opposite side. The threaded trunk is assembled extremely simply and quickly.

Casing thread
Both core and casing pipes are threaded, from one end to the outside, from the other to the inside. This allows you to quickly and easily assemble the casing. The dimensions of the threads are unified - any casing can serve as a core pipe, just screw the crown and top to it

There are casing pipes designed for welded joints. They are not used in the private sector due to the laborious process of column assembly.

Both casing and core pipes are made of steel grade 45 with strength group "K". To increase resistance to surface wear, the ends of the pipes are hardened. Depending on the drilling equipment used and diameter submersible pump in the device of private water intake openings, pipes with a diameter of 100 to 200 mm are used.

Core Drilling Stages

Before starting work, you need to study the cadastral plan and prepare the work surface. It is necessary to ensure unhindered access to the drilling site of both the drilling rig itself and the machine with flushing fluid.

The next step will be digging a pit with a volume of at least 2 cubic meters - this will avoid the need to use an additional tank. The pit is designed to drain groundwater and spent flushing fluid. To install the main part of the trunk, it is necessary to punch the soil.

Next, the selected crown is connected to the core drill pipe and the selection casing pipewhich will deepen as they deepen. The installation should be firmly fixed, after which the drilling rig is launched.

Direct and reverse flush column technology
Column technology with washing the bottom of the water with the most simple and quick way to free the working shaft from the destroyed rock

As the core drill is deepened and filled, it is periodically lifted to the day surface and cleaned from soil captured by the tool during drilling. Then the core freed from the core can again be immersed in the hole of the well to continue drilling.

To climb up the drill string, consisting of a core projectile and rods, dismantled. That is, the bar after the bar is sequentially separated until the core tube is removed from the barrel.

The best option for developing a well to private traders is core drilling, followed by flushing. No samples should be taken in this case. The main thing is to quickly form the barrel and clean it of sludge. At the same time development work for the upcoming operation.

For washing, you can use any water, it is quite suitable from a nearby pond or river. Drilling can also be done dry if a sand well is being developed. Usually in this case, a pair of buckets of water as a drilling fluid is sufficient only to cool the shell at the bottom.

Column technology in construction
According to the core technology, holes are drilled in concrete and reinforced concrete structures, foundations and brick walls.

When working in loose, low-moisture sand, to strengthen the walls of the hole in the working solution, it is recommended to add liquid glass or clay mass. In any case, when the drill passes through the horizon with an unstable structure, it is justified to strengthen the walls of the well with casing pipes.

Technological features of the process

During the deepening process, it is possible to adjust the speed of the drill. It should be noted that the layers of sedimentary rocks drill easily overcomes at low speeds. But when passing the indigenous rock formations, an increase in the frequency of rotation is required. With the core drilling method, it is possible to pass formations of various compositions and of any hardness.

It is necessary to take into account the fact that the drilling rig should be located on a prepared, leveled horizontal platform. The angle of penetration can be adjusted if the diameter of the hole being developed does not exceed 1 meter. Then the verticality of the production is supported by the casing.

Casing pipes can be reused if, right after sinking, they are removed from the mine. A core tube is a reusable shell, which cannot be said for crowns. Drilling in the sedimentary horizon requires at least two, or even more. When constructing a well on limestone, it is impossible to predict the number of erased crowns with accuracy.

Rock drill bit
In order to extend the life of the diamond core after it has been installed or replaced, the bottom of the well must be treated with a chisel. This measure will significantly increase the rate of penetration.

The drilling rig can be mounted on vehicles with a high carrying capacity or on a caterpillar special equipment in case of work in difficult terrain. Lighter mobile equipment can be used for core drilling of water wells.

Advantages and disadvantages of the column method

Due to the point action of the crown, accurate cutting and removal of a single core on the surface is ensured along its radius. The technology is applicable for drilling up to XII categories, you can work both perpendicularly and at an angle.

One of the most important indicators of the core method is considered high productivity and drilling speed.

In addition, the following advantages can be distinguished:

  • The volume of drilling in the case of using flushing fluid or process water is 85%;
  • The introduction of active emulsions into the working solution makes it possible to retain the walls of the well in its original state;
  • Due to the reduction of axial loads due to the fact that the rock is not destroyed in a continuous, a reduction in energy costs is achieved.
  • The method allows you to work with any rocks, including basalt and granite.
  • When using the precast mobile machine, it is possible to carry out work in hard-to-reach places.

Along with the advantages, core drilling also has its drawbacks:

  • When working in fractured rocks, core jamming often occurs, which leads to the need to remove the pipe to knock it out.
  • During the passage of hard rocks due to overheating and grabbing the crown quickly dulls. To avoid this, it is necessary to use coolant and reduce the feed rate. As a result, the drilling speed is reduced.
  • Small cross-section (up to 200 mm) of drilling does not allow the use of powerful submersible pumps.

When developing wells for water in the case of using a clay solution during the opening of the reservoir, there is a high probability of siltation of the aquifer.

Conclusions and useful video on the topic

Video 1. The initial stage of well drilling by the core method:

Video 2. Core drilling in granite rock:

The start of core drilling operations should be preceded by an economic calculation. Compliance with safety standards and equipment operating rules minimizes the risk of its failure, thereby ensuring high efficiency, drilling speed and lowering economic costs.

Do you want to share only the well-known subtleties of column technology with you? Do you have useful information on the topic of the article? Please write comments in the block form below, ask questions and post photos on the topic of the article.

Was the article helpful?
Thanks for your feedback!
No (14)
Thanks for your feedback!
Yes (93)