This stage consists in drilling a pilot hole along a pre-designed customer approved drill path. The pilot hole can be drilled from surface to surface, between trenches or pits.

The selection of the tools that make up the drill string which will be used depends fundamentally on the composition of the predominant soil strata to be drilled.

Entry pit

Installation of casing during pilot hole drilling

Pilot hole exit

Down hole assembly including non mag section and bent sub

Downhole mud motor

Drilling bit, tricone bit

Duck bill Bit with hydraulic injection

Drilling ramp

Exit swabbing

TRACKING/SURVEYING

The drilling tool must be guided along its underground path and to that end three different tracking methods are used:

1.- Tracking with walkover system

Repeater

Receiver

Probe emitting radio frequency signals

2.- Electromagnetic wire line tracking

In this system the probe emits signals corresponding to its inclination, dial position and magnetic azimuth. These signals are transmitted by means of electronic impulses which travel through a cable threaded through the drill string to the drillers’ cabin. Here they are decoded within an interface which feeds the computer and by means of a program then shows the location of the probe.

Surveyor with computers

Control screens- Driller

Machine Screens Controller

Magnetic grid or solenoid verification system

So as to achieve greater control of the drill path, electromagnetic guidance systems are linked with the layout of an electrified coil on ground surface. This coil creates an independent magnetic field which allows for a better control of the drill path depth and advance by means of triangulation.

Surveying

Cable layout

Control with theodolite

Solenoid

Tracking system with Gyrocompass

A gyrocompass is a nonmagnetic compass constructed so as to be able to use the precision of its effect in the guidance of more complex directional drilling. It travels in the probe inside the nonmagnetic housing, and, as do the electromagnetic systems, feeds and connects with computers in the control cabin through cables threaded through the drill pipe string. Even though less frequently used because of its greater operational complexity, in combination with accelerometers, it provides an extremely accurate tracking tool, possessing three significant advantages over the magnetometers:

• it finds the true north in accordance with the Earth’s rotation, which is different and more useful than the magnetic north,
• it is not affected by ferromagnetic materials, such as rocks of volcanic origin or neighboring metallic elements or pipelines, which change the magnetic field,
• it allows precise tracking below large water surfaces

In order to recondition the borehole to a diameter that coincides with the product which will be inserted, it should be reamed until it reaches a diameter 50% larger in small pipes or 12 inches more in the case of bigger pipes. The type of soil of the crossing establishes the choice of reamers, these can be:

1. Open fly cutters
2. Crown reamers with inserts or teeth
3. Conical reamers

Open fly cutter

Reamer with rotating teeth

Conical and aggressive maxi fly cutters for clay and sand

Centralizer

It is important to maintain a permanent injection of drilling fluids during all stages, as this will remove the clay, sand or whatever soil content is being drilled.

Open borehole

Reamer

Swabbing and Cleaning of the Borehole

A cleaning swab in the form of a cylinder is passed through the borehole walls in order to homogenize and prepare them for a smooth and safe insertion.

End of reaming

Cylindrical barrel reamer- swabbing run

Fly Cutters

This is the final stage and the one which we have been working for. The installation of the pipeline inside the borehole is the most critical stage, as the borehole is gradually occupied by an element alien to the drilling process and precautions should be increased so as to facilitate its smooth insertion.

The pipeline should be constructed behind the insertion pit on a path aligned with the axis of the borehole. It has welded joints covered with shrink sleeves ready for pullback. Pertinent hydraulic and caliber tests are carried out before the pullback.

Pipeline alignment on cleats

Hydraulic testing on cleats

Drilling head

Pipeline on rollers

Calibration run on rollers

Placement of heat-shrinkable sleeves

Pipe connection through a pulling head and a swivel

Formation of swan neck, breakover

Integrity testing for the pipe lining with Holliday collar

Positioned pipeline

Inserted pipeline-towing head removal to allow for testing

The rig begins the pullback, rotating the reamer and pulling the pipeline as drill pipes are removed until the reamer and the pipe arrive at the foot of the rig. The down hole pumping of drilling fluids continues throughout the pullback process.

Beginning of pullback

Pullback

When the product pipe slides into the borehole full of mud, it begins to float, helping to reduce the required pull force.

Entry pit

Swan neck breakover

Sideboom with pipeline

Support with lifting device

The pipe is pulled back from the rig. The pipeline, welded to the drilling head attached to a swivel, follows the reamer’s path through the borehole without rotating until it reaches the entry point of the rig.