Horizontal drilling

Horizontal drilling  and  Horizontal directional drilling  (HDD or English  HDD  from  horizontal directional drilling ) is a common trenchless method   (English) Russian. laying underground communications, based on the use of special drilling complexes (rigs). The length of the laying of tracks can be from several meters to several kilometers, and the diameter can be up to 1200 mm or more. To protect communications, pipes made of polyethylene (HDPE), steel and other materials are used.

Story

Horizontal drilling, which has become revolutionary in construction, was invented in 1963 by Martin Cherrington as an alternative to the traditional trenching method for laying communications.

Technology of trenchless construction of underground utilities

Before starting work, the properties and composition of the soil, the location of existing underground utilities are carefully studied, and appropriate permits and approvals for underground work are issued. Selective sounding of soils is carried out and, if necessary, drilling of especially difficult intersections of the drilling route with existing communications. The results of these works are of decisive importance for the choice of the trajectory and tactics of well construction. Particular attention is paid to the optimal location of drilling equipment at the construction site and ensuring safe working conditions for the drilling crew and the surrounding people.

The construction of underground utilities using the technology of horizontal directional drilling is carried out in four stages:

• pilot well drilling,
• sequential expansion of the well,
• pipeline pulling,
• The final stage.

Stages of construction of underground utilities

Pilot well drilling

Drilling a pilot well is a particularly important stage of work, on which the final result largely depends. It is carried out using a rock cutting tool — a drill head with a bevel in the front and a built-in emitter.

The drilling head is connected by means of a hollow body to a flexible drive rod, which makes it possible to control the construction of a pilot well and bypass underground obstacles identified at the drilling preparation stage in any direction within the natural bend of the pulled working line. The drilling head has holes for supplying a special drilling fluid, which is pumped into the well and forms a suspension with crushed rock. The drilling fluid reduces friction on the drill head and rod, protects the well from collapses, cools the rock cutting tool, destroys the rock and cleans the well from its debris, bringing them to the surface.

Control over the location of the drill head is carried out using the receiving device of the locator, which receives and processes the signals of the transmitter built into the body of the drill head. The locator monitor displays visual information about the position, slope and bearing of the drill head. This information is also displayed on the rig operator’s display. These data are decisive for monitoring the compliance of the trajectory of the pipeline under construction with the design one and minimize the risks of breaking the working thread. When the drill head deviates from the design trajectory, the operator stops the rotation of the drill rods and sets the bevel of the drill head in the desired position. Then the drilling rods are crushed without rotation in order to correct the drilling trajectory.

The construction of a pilot well is completed with the exit of the drill head at the point specified by the project.

Drill rod (BS) is a pipe with a diameter of 50-80 mm and a length of 2-6 meters. At the ends of the BS, CONICAL threaded connections with external threads are cut, and at the opposite end — with internal threads. The BS has one very important element, without which it would be impossible to change the direction of the pilot well, this is a bellows insert (connection). Each BS has two such connections. In general, technologically, this is more like a knurling on a pipe than some kind of insert welded into the BS.

In the drilling machine, the BS are screwed sequentially, one into the other, as the drilling head advances. Thus, interconnected BSs are similar to a flexible cable used to clean sewer pipes. The principle of changing direction

The principle of changing the direction of movement of the drill head in the horizontal and vertical planes follows the principle of a flexible cable: if its free end is not fixed (if it is fixed, then this is already a “flexible shaft”), that is, it will always be slightly bent.

The operator on the display of the portable receiver «sees» the angle of rotation of the drill head (that is, the «free end of the cable») and its direction, and, if it is necessary to «turn» the direction of the well, issues a command to the operator of the drilling machine «stop» and then «Turn to N ../degrees» (but only in one direction — in the direction of tightening the BSh threads!) so that the drill head lies in the right direction. Further, at the command of the operator of the remote control, the drill head is “pressed” into the ground at the angle of the desired trajectory, then the operator of the drilling machine turns on the supply of flushing fluid — usually water — and the longitudinal supply with rotation. The flushing fluid is supplied under controlled pressure through the drilling machine spindle to the BSH and further to the drilling head. The drilling head is drilled into the ground to the required trajectory.

Well expansion

The expansion of the well is carried out after completion of the pilot drilling. The drilling head is detached from the drill rods and a rimmer is attached instead of it — a reverse action expander. By applying traction force with simultaneous rotation, the rimmer is pulled through the wellbore in the direction of the drilling rig, expanding the pilot well to the diameter required to pull the pipeline through. To ensure unhindered pulling of the pipeline through the expanded well, its diameter is 50-100% larger than the diameter of the pipeline.

Pipeline pulling

On the side of the well, opposite from the drilling rig, there is a string of pipeline ready for pulling. A head is attached to the front end of the whip with a swivel and a rimmer that perceives the traction force, and at the same time does not transmit rotational motion to the pipeline. Thus, the drilling rig pulls a string of the pipeline being drawn into the well along the design trajectory.

Cementing

When laying a pipeline in difficult geological conditions, the annular space is cemented by pumping a cementing slurry there under pressure by a special machine.

The final stage

After the completion of the main technological stages, the engineering and technical staff submits to the customer the as-built documentation, which indicates the actual position of the laid pipeline in various planes, with the obligatory indication of «bindings» to landmarks on the ground.

HDD installations

HDD installations (machines) are complex construction equipment. A typical machine includes a frame, a body, a running gear (tracked or wheeled), a power plant (diesel engine), a hydraulic station, a rod feeder, a drilling carriage, a control panel (operator’s workplace).

Installations are classified according to the maximum pulling force, measured in tons. Other important characteristics that are indirectly related to it are the maximum expansion diameter and the maximum drilling length.

Secondary indicators that can characterize the consumer qualities of a HDD installation are the bending radius of the rod string (shows how much the pilot drilling trajectory can be changed), as well as the consumption of bentonite solution (l./min., shows how often it will be necessary to replenish the tank of the mixing device for drilling mud preparation).

Mini HDD units

Mini HDD rigs are compact HDD rigs for controlled puncture under the road. Mini HDD installations allow laying communications without disturbing the landscape. Bring communications in hard-to-reach places, from a well, from a pit in cramped conditions. Mini HDD installations are lighter in weight and compact in size, pulling force up to 50 tons, puncture length up to 100 meters.

Location system in HDD as a management tool

Management in HDD is a very important point. The drill is out of sight and reach during operation, and uncontrolled drilling can lead to unpredictable consequences. Therefore, in the production of HDD works, location systems are used to control the drilling process. The location system is a probe, which is located on the drill head, and a special synchronization device with this probe, which is in the hands of the operator of the location system (locator) on the earth’s surface. The probe records all information about the angle and direction of drilling, the number of revolutions and the temperature of the drill head. This information is transmitted during the drilling process to the locator and prevents undesirable consequences.

Drilling fluids for horizontal directional drilling

Powder for production of HDD drilling fluid and expander.

HDD specialists devote a lot of time to improving the quality of drilling fluids when drilling horizontally directed wells. It is known that the drilling fluid has a great impact on the productivity and efficiency of the entire process: the speed of drilling, the environmental situation, and the safety of work. In HDD, the quality of the drilling fluid guarantees 70–80% of the successful completion of works on laying communications.

When working in sandy soils, HDD specialists often face the problem of filtration and water absorption, this is due to the properties of the soil itself, since sand is porous and highly permeable by nature. As for shale clays and loams, often found in drilling sites, when exposed to water, these types of rocks become sticky and swell. The result of such processes may be the loss of fluid circulation, jamming and jamming of the drilling tool, which leads to the impossibility of further work with the so-called «tool sticking».

To avoid these problems, bentonite drilling fluids and various components are used to eliminate complications, clay inhibitors or stabilizers, lubricant additives to lubricate the tool and borehole walls to facilitate penetration, polymers that thicken the drilling fluid to maintain its required viscosity.

Most HDD operators use bentonite-based «single-bag» multi-component mixes to facilitate the preparation of low solids drilling fluid on site.

At large facilities, the solution is prepared individually, according to the geological and technological line (GTN), the diameter of the pipe being drawn, the composition of the soil, the pump power and the traction force of the installation.

Main benefits of operation

Production and technical aspect

• The possibility of trenchless construction, repair and sanitation of underground utilities:
  • under rivers, ravines, forests; in specific soils (rocks, floating rocks);
  • in security zones of high-voltage overhead power lines, main gas, oil, product pipelines;
  • in conditions of dense housing development of cities when the route passes under highways, tram tracks, highways, squares and parks;
• Reducing the time and volume of organizational and technical approvals before the start of work due to the absence of the need to stop the movement of all types of land transport, blocking roads and railways;
• Significant reduction of work execution time due to the use of high-tech drilling complexes;
• A significant reduction in the number of heavy equipment and labor involved in laying pipelines;
• Reducing the risk of emergency situations and, as a result, guaranteeing the long-term safety of pipelines in working condition;
• No need for external energy sources in the course of work due to the complete autonomy of the installations;
• No need to carry out work on dewatering in conditions of high groundwater.

Financial and economic aspect

• Reducing the estimated cost of pipeline construction by reducing the time of work, the cost of attracting additional labor and heavy earthmoving equipment;
• Minimization of energy supply costs for drilling complexes due to the efficiency of the units used;
• Absence of costs for the restoration of damaged sections of roads and railways, green spaces and urban infrastructure;
• Reducing operating costs for monitoring and repairing pipelines during operation.

Social and environmental aspect

• Preservation of the natural landscape and ecological balance at work sites, exclusion of technogenic impact on flora and fauna, erosion of coasts and bottom sediments of reservoirs;
• Minimization of the negative impact on the living conditions of people in the work area.