Geops-Bolkan Drilling Services perform large-diameter drilling in the Balkans

July 17, 2019

by Ilian Valkov Eng., Executive Manager at Geops-Bolkan Drilling Services Ltd

One of the challenges of modern geological research is to identify the quality features of valuable resources at an early stage. The extraction of sufficient material for the initial technological research provides an opportunity to obtain critical data about the properties of the prospective commodities. Expertise in ore enrichment is important for the effective planning of detailed researches and project stabilization, as well as the reduction of investment risk.

In this context, only large-diameter drilling provides sufficient material to carry out research and analyses and obtain technological samples at an early stage of project development. This form of drilling is becoming increasingly popular.

Geops-Bolkan Drilling Services Ltd (‘Geops’) is a Bulgaria-based drilling contractor, with the largest drill-rig fleet in Eastern Europe, serving the mining and mineral exploration sectors. Their extensive operations in the Balkans have been a key factor in the company’s increasing strength, growth, and reputation.

A new project in the Balkans

In 2018 Geops was challenged to execute a large-core drilling program for a major mining company. This program was part of one of their long-term projects in the Balkans. The scope of work demanded one borehole 444 mm in diameter and 292 mm of core to be conducted to a depth of 623 m.

First core run

Bespoke Engineering

No suitable equipment was found on the market, so Geops designed and produced something that would accomplish the goal.
The final result was a triple-tube conventional core barrel with an outer diameter of 444 mm that can collect three meters of 292-millimeter diameter core. When empty, the core barrel weighs 1500 kg and when full, 1800 kg. A special drill-bit design with diamond inserts was devised for the job.

To complete the challenging 623-meter large-diameter borehole, a big drill rig was needed. Atlas Copco’s RD20IIIXC drilling machine with a pull-back capacity of 50 tonnes was requested and successfully implemented. A special drilling mud system of 40 m3 was designed and provided by Geops, with two duplex mud pumps NB125 and two 220 kVA generators to supply the necessary power.

Full core barrel

All was set and drilling started in August 2018. Choosing a 17 1/2-inch (444.50 mm) drilling diameter for coring allowed the team to switch from mud rotary drilling to core drilling without involving any additional operations, like casing and reaming. This way, the core could be extracted at any desired interval of mineralization and that was very valuable and cost efficient for the client. To cover the overburden an 18 5/8-inch (473.07 mm) casing was installed to a depth of 50 m. The first series of large-diameter conventional coring started at 293 m and was finished off by the geologists to a depth of 335 m. From 335 m to 480 m mud rotary drilling was used with the same 17 1/2-inch (444.50 mm) diameter drill bit and then from 480 m coring was begun again until the end of the hole was reached, which was at 623 m. A total length of 185-meter core with a volume of 12.4 m3 was recovered, weighing approximately 37 tonnes.

The mud rotary drilling was as fast as usual, and the production from the section of coring was around 12 m and 6 m, at shallower and deeper sections respectively. Core recovery of more than 95 % was achieved. At depth of 600 m, the core breaking force reached 28 tonnes (pull-out).

The biggest challenges faced by the company were using a prototype on-site and achieving a high percentage of core recovery. Despite such obstacles and the particular geology, complicated even for wireline drilling, all goals were met.

Drilling was carried out in accordance with the requirements and safety standards of the client and with zero incidents.

Geops’s drill site

About the company

Geops-Bolkan Drilling Services Ltd was established in 2004 with a focus on surface and underground drilling for the exploration, mining, and geological industry. In order to satisfy its customers’ needs, the company continuously invests and expands the range of its proposed drilling services. Over the years, it has strengthened its position of being a reliable and trustworthy drilling contractor for many investors in the Balkans, Central Europe, and North Africa.

The corporate head office is located in Asenovgrad, Bulgaria. The company has established a network of regional offices in the territories of Serbia, Macedonia, Bosnia and Herzegovina, Poland, Tunisia, Germany, and soon (by June 2019) Peru and Chile.

Geops has both ongoing and successfully completed surface and underground drilling projects in more than 12 countries around Europe and North Africa.

Drilling capabilities

Exploration and mining companies rely on the availability of Geops’s full range of drill rigs for various drilling methods and terrains (40+ rigs). The company has a wealth of experience in diverse drilling conditions and expertise in project management, application of the latest and best drilling practices, wellestablished drilling crews with the drillers having five years of experience on average, vastly experienced rig maintenance and rig engineering crew, and a fully equipped rig and spare parts production facility.

Geops’s current fleet of drill rigs is expanding to enable the company to work at various locations, increasing its knowledge of different countries and jurisdictions, and targeting new markets.

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