UK manufacturer Dando Drilling International's latest mid-sized top-drive rotary rig, the Multitec 4000, is experiencing strong sales worldwide and has been enjoying particular success in Central and South America.

"I think there are a number of reasons for this," explains Alberto Villanueva, Dando's sales engineer in charge of the region. "Customers are looking for a robust rig from a trusted brand, and there is an increasing a need for multipurpose machines that are powerful enough for depths in the 0-200m range and that require less initial investment than traditional equipment."

With budget constraints continuing to be present throughout the industry, drill teams don't always have the luxury of one rig for one application anymore. Villanueva continues: "They expect a rig that is excellent at all applications. They want to do coring one day, SPT tests the next, or open-hole air-flush another. Versatility provides value."

Plant requirements

One recent case serves to illustrate the usefulness of versatile machinery. Nestled in the midst of a stunning landscape of mountains and lush flora in central Bolivia, the Corani company manages hydroelectric plants that provide electricity to the department of Cochabamba. A partnership of the national electricity corporation ENDE and private stakeholders, the company oversees two hydroelectric power facilities and all of the connected water resources. These include rivers, aquifers, and natural as well as artificial lakes.

Over 35% of total electricity supply in Bolivia is currently provided though hydropower. Further expansion is in progress with the aim of exporting power as well as meeting national demands. Drilling is essential for Corani in the maintenance and development of the project.

"The customer was looking for a rig on a small footprint that could manoeuvre into limited-access areas. But they needed the power to drill deeper than other small rigs on the market could manage," Villanueva claims.

Corani's requirements for the drilling programme were manifold. It required geotechnical information on the geology at depths of up to 150m, with occasional 200m holes; site investigation tests including standard penetration tests (SPT) to monitor existing infrastructure and prepare for new development along its waterways and dams; and, finally, it wanted information on aquifer resources and, in particular, needed to run packer tests to monitor hydraulic conductivity along certain sections of a drilled well.

Corani's Multitec 4000

The Multitec 4000 rig is suitable for this kind of work. The latest Mk3 version of the rig sits on a crawler base that is only 1.6m wide, allowing access between closely spaced trees, boulders or buildings. The rig has been designed from the ground up to keep the centre of mass as low and as close to the middle of the rig as possible to ensure safe tracking over steep or undulating terrain.

Corani makes use of the versatile rotary head and high-speed wireline winch for coring, while the high torque of the head allows open-hole boring required to install inflatable packers when conducting aquifer investigation. Villanueva was impressed by the versatility of team and rig during a recent visit to Bolivia, where he says they often change drilling methods from day to day.

Prior to their purchase of the Multitec 4000 Corani would contract outside companies to complete its drilling needs. Running its own rig has greatly reduced drilling costs, and the efficiency of the design, which includes a Bosch-Rexroth-powered hydraulic system, ensures running and maintenance expenses are kept low.

The Multitec 4000 has a modular design, and there are a number of rotary head options from 750rpm to 6000Nm of torque. The rig supports coring, reverse circulation (RC), aircore, down-the-hole hammer and rotary air blast drilling (RAB), as well as conventional open-hole mud rotary.

Corani often requires angled boreholes, so the mast dump facility and capability to drill between 45° and 90° were essential. The Multitec 4000 comes with two mast options. The standard mast chosen provides 4t of pullback; however, a heavy-duty option is equipped with 6t should greater depth or diameter be required. The Corani drillers run 3m-long drill rods, and a swing-out mast extension lets them trip two rods at a time in lengths of 6m to save time.

There are also multiple engine options. The latest MK3 version can be supplied with a Kohler 75HP Tier 4 Final, which meets European and North American standards, and a Perkins 111HP Stage 3A for the rest of the world where the best quality diesel fuel may not be available.

As much of Corani's work is for site investigation around its hydroelectric infrastructure, a percussive hammer was fitted to the rig. This is mounted on a three-position hydraulic carriage, which allows the rotary head to be slid out of the way and the hammer unit into position. A third position provides for a clear line of site from the winch down to the borehole.

The percussive hammer is a special design that ensures the weight of the unit is supported above the drill string and therefore only the hammer strike drives rods during testing, providing more accurate results when the geotechnical engineers require SPT data. The hammer can also run Dando's Duplex Drive (3D) system, which enables simultaneous casing and sampling in softer geologies where undisturbed samples are needed.

Sales director Quentin Dulake adds regarding the Multitec 4000 Mk3: "This is not just a good multipurpose rig. We have the performance of a dedicated wireline rig, or a dedicated RC aircore rig, or a dedicated RAB rig, all from one ultra-versatile platform."

Villanueva says he is busier than ever supporting customers in what he considers a market experiencing growth. "We have recently delivered Multitec 4000 models to Peru and Chile as well as Bolivia and have another four currently in build for this region."