How Dual-Rig HDD Completed the AKK River Niger Crossing

The Ajaokuta–Kaduna–Kano (AKK) Gas Pipeline is one of Nigeria's major gas infrastructure projects, designed to improve natural gas transportation to central and northern parts of the country. Its development is intended to support power generation, industrial activity and wider access to domestic gas.

Completing a major pipeline involves more than installing pipes along a planned route. Difficult sections, particularly river crossings, can require specialist engineering methods and equipment.

One of the most challenging sections of the AKK Gas Pipeline was its crossing beneath the River Niger. The project required a 40-inch gas pipeline to be installed along a 1,565-metre underground route through mixed sand, gravel and rock formations.

PCE Nigeria was appointed to execute the crossing using dual-rig intersecting technology, a specialist Horizontal Directional Drilling (HDD) method that enables drilling operations from opposite sides of an underground crossing.

Combined with synchronous reaming, high-capacity drilling equipment and a specially developed drilling-fluid formulation, this approach enabled us to complete the River Niger crossing on 26 July 2025.

The project provides an example of how specialist HDD technology, geological understanding and coordinated field operations can be applied to demanding pipeline construction.

The AKK River Niger crossing presented several technical challenges that influenced the engineering approach. The underground route extended 1,565 metres and reached a depth of approximately 16 metres.

Along this route, drilling equipment had to pass through sand, gravel and rock formations. Each material behaves differently during drilling, affecting cutting resistance, borehole stability and the removal of excavated material.

Loose sand and gravel can make it difficult to maintain stable borehole conditions, while rock formations require suitable drilling tools and effective cuttings transport. Changes between geological formations can also affect drilling resistance, fluid circulation and steering performance.

The 40-inch pipeline introduced additional requirements because the pilot hole needed to be enlarged sufficiently to accommodate the pipeline during installation.

For a crossing of this scale, engineers had to consider the planned drilling alignment, geological conditions, drilling-rig capacity, guidance accuracy, borehole enlargement, fluid circulation and pipeline pullback requirements.

Our engineering approach combined dual-rig intersecting technology, synchronous reaming and specially developed drilling-fluid systems to address these requirements.

Horizontal Directional Drilling (HDD) is a trenchless construction method used to install pipelines and underground utilities beneath rivers, roads, railway lines and other obstacles without excavating an open trench across the entire route.

In a conventional HDD operation, a drilling rig creates a pilot hole from one side of the crossing towards the other. Once the pilot hole is completed, the borehole is enlarged through reaming before the prepared pipeline is installed.

Dual-rig intersecting technology uses drilling rigs positioned on opposite sides of the crossing. Each rig drills towards a planned underground intersection point, while specialist guidance systems help the drilling teams control the direction of the two pilot holes until they meet and establish a continuous underground route.

This method may be considered for long-distance or technically demanding HDD crossings where drilling the entire pilot hole from one side presents significant engineering challenges.

Operating two rigs requires additional coordination because both drilling teams must maintain accurate alignment information, monitor drilling performance and ensure that the underground paths connect within the planned bore geometry.

The method therefore depends on suitable drilling equipment, guidance accuracy and coordinated field execution.

For the AKK River Niger crossing, we used dual-rig intersecting technology during pilot-hole drilling. Instead of drilling the entire 1,565-metre route from one riverbank, we conducted drilling operations from opposite sides of the crossing.

The pilot holes were guided towards an underground intersection, establishing the route required for subsequent borehole enlargement and pipeline installation. This method formed part of our engineering approach to the crossing length and mixed geological conditions.

Accurate alignment was particularly important because the drilling paths needed to connect underground while maintaining suitable geometry for the 40-inch pipeline.

The operation also required close coordination between the drilling teams. Changes in geological conditions, drilling resistance or equipment performance on one side could influence decisions about the operation on the opposite side.

By coordinating the drilling equipment, guidance systems and field teams, we established the pilot-hole route needed for the subsequent construction stages.

Guidance systems play an important role in HDD construction by helping engineers monitor the position and direction of the drilling assembly. For dual-rig intersecting operations, accurate guidance becomes particularly important because two independently drilled pilot holes must meet underground.

Each drilling team needs reliable information about the position of its drilling assembly relative to the planned alignment. This information supports steering adjustments as drilling progresses.

When geological formations change, drilling resistance or tool behaviour may also change, making continuous monitoring important.

For the AKK crossing, we used specialist guidance systems alongside our drilling rigs and coordinated field operations to maintain the required underground alignment and establish a continuous pilot hole suitable for reaming and pipeline installation.

Completing the intersecting pilot hole establishes the underground route, but the opening is not yet large enough to accommodate the pipeline.

The next major stage is reaming, which enlarges the borehole to the diameter required for installation. During reaming, specialist cutting tools remove additional soil or rock along the established alignment. For a 40-inch pipeline, borehole enlargement can involve substantial excavation and increased demands on drilling equipment and fluid circulation.

The reaming process must account for geological conditions, cuttings removal, equipment loads and the stability of the underground opening.

For the AKK crossing, we used dual-rig synchronous reaming, coordinating drilling operations from both sides of the River Niger during borehole enlargement.

Although dual-rig intersecting and synchronous reaming both involve two rigs, they serve different purposes. Dual-rig intersecting establishes the pilot-hole alignment, while synchronous reaming enlarges the underground opening for the pipeline.

Reaming is an important part of large-diameter HDD construction because the borehole must provide sufficient clearance for pipeline installation. The drilling equipment must remove excavated material while maintaining suitable borehole conditions.

In mixed geological formations, the operation becomes more demanding. Sand and gravel may present stability and fluid-loss challenges, while rock formations require suitable cutting tools and sufficient drilling capacity.

Our dual-rig synchronous reaming approach involved coordinating equipment from opposite sides of the crossing. This formed part of the engineering strategy for managing the borehole enlargement required for the 40-inch pipeline.

Successful reaming also depends on factors beyond rig capacity. Effective drilling-fluid circulation, cuttings removal, suitable tooling and continuous monitoring are important throughout the operation. For AKK, the reaming process prepared the underground route for the final pipeline pullback.

Dual-rig drilling and synchronous reaming depend on more than mechanical equipment. As drilling progresses, excavated material must be transported out of the borehole while suitable underground conditions are maintained.

This is one of the main functions of HDD drilling fluid. It helps transport excavated soil and rock towards the surface, support borehole stability, cool and lubricate drilling tools, reduce friction and maintain conditions required for effective borehole enlargement.

The AKK River Niger crossing passed through sand, gravel and rock, creating different drilling-fluid requirements along the route. We used a specially developed drilling-fluid formulation suited to the project's geological conditions.

Bentonite is commonly used in HDD drilling fluids because it helps develop viscosity and filtration-control properties. Specialist additives may also be required to manage fluid loss, cuttings transport and other drilling challenges.

Our Brighter Star drilling-fluid range includes BRSBENT SQ activated bentonite and specialist additives for different underground construction conditions.

For the AKK crossing, drilling-fluid engineering formed part of the wider construction approach alongside equipment selection, guidance, drilling and reaming operations.

After pilot-hole drilling and reaming, the prepared pipeline was installed through the completed underground bore. This stage is known as pipeline pullback, during which the pipeline is drawn through the borehole while the construction team monitors installation conditions and manages the forces acting on the pipe.

For large-diameter pipelines, engineers must consider pipeline weight, friction, borehole geometry, bending limitations and coating protection.

The drilling equipment must also provide sufficient pulling capacity for the planned installation. On the AKK crossing, we used high-capacity HDD equipment and coordinated field operations to support installation of the 40-inch pipeline over the 1,565-metre route.

Work began on 25 March 2025, and we completed the River Niger HDD crossing on 26 July 2025, connecting an important section of the wider AKK Gas Pipeline.

Dual-rig intersecting technology enabled us to establish the underground pilot-hole route through coordinated drilling from opposite sides of the River Niger. Together with synchronous reaming, specialist guidance systems, high-capacity equipment and drilling-fluid engineering, the method formed part of our construction approach.

The experience offers several practical considerations for future HDD projects.

Drilling Methods Must Reflect the Crossing Conditions

Not every HDD crossing requires a dual-rig arrangement. Shorter or less demanding crossings may be completed using a single rig, while longer or more complex installations may require specialist methods. The selection depends on crossing geometry, geological conditions, equipment capacity and wider construction requirements.

Equipment and Guidance Must Work Together

The success of an intersecting operation depends on more than drilling power. Accurate guidance and coordination are important for maintaining alignment and bringing the pilot holes together underground.

Borehole Enlargement Requires Careful Planning

Completing the pilot hole does not guarantee that the final pipeline can be installed. Reaming, cuttings removal and borehole conditioning must be planned around the pipeline diameter and geological conditions.

Drilling-Fluid Performance Supports Every Stage

Drilling fluid contributes to cuttings transport, borehole stability and the effectiveness of drilling and reaming operations. Its formulation and circulation must be suited to the changing conditions along the crossing.

Field Coordination Is Essential

Dual-rig operations require effective communication and coordination between equipment operators, guidance teams and drilling-fluid personnel. These activities must work together throughout construction.

What is dual-rig intersecting technology?

Dual-rig intersecting technology is an HDD method in which drilling rigs operate from opposite sides of a crossing. Their pilot holes are guided towards an underground intersection to establish a continuous drilling route.

Why were two HDD rigs used on the AKK project?

The dual-rig arrangement formed part of our engineering approach to the 1,565-metre crossing and its mixed sand, gravel and rock formations. It allowed pilot-hole drilling from opposite sides of the River Niger.

What is the difference between dual-rig intersecting and synchronous reaming?

Dual-rig intersecting is used to establish the pilot-hole route by connecting drilling paths underground. Dual-rig synchronous reaming involves coordinated operations from both sides during borehole enlargement.

How long was the AKK River Niger HDD crossing?

The crossing extended 1,565 metres and involved installing a 40-inch gas pipeline beneath the River Niger.

Why was drilling fluid important during the AKK crossing?

Drilling fluid helped transport excavated material, support borehole stability and maintain suitable drilling conditions through mixed geological formations.

When did PCE Nigeria complete the AKK River Niger crossing?

We completed the specialist HDD crossing on 26 July 2025, following commencement of work on 25 March 2025.

The AKK River Niger crossing provides an example of how specialist Horizontal Directional Drilling technology can be applied to a technically demanding pipeline installation.

Its underground route, large pipeline diameter and mixed geological formations required careful planning, equipment selection and coordinated execution.

By combining dual-rig intersecting technology, synchronous reaming, specialist guidance and drilling-fluid engineering, we completed the underground crossing and connected an important section of the wider pipeline route.

For future pipeline projects involving long-distance crossings, large pipeline diameters or complex ground conditions, the methods used on AKK provide a practical reference for specialist HDD engineering.

At PCE Nigeria, our services include HDD engineering and construction, high-capacity drilling equipment, pipeline EPC services and technical support for underground pipeline installations across Nigeria.

Planning a long-distance HDD river crossing or large-diameter pipeline project?

Explore our HDD capabilities or contact our technical team to discuss your project requirements.

Project enquiries: wanyang@pcenigeria.com