Directional drilling is a relatively new aspect of exploration technology in the mineral resources industry. While technology still needs to advance if its application is to be successfully integrated into the hard rock environment, it has significant implications for cost and time saving in exploration. It also has the potential to enhance exploration efficiency and production greatly.

Murray & Roberts Cementation is at the forefront of developing directional drilling technology at depth and in a hard rock environment. Martin Bevelander, surface drilling manager at Murray & Roberts Cementation, explains that the directional drilling technology had its birth in the oil industry some 25 years ago. "Oil reservoirs were often located in positions that were not accessible by ordinary surface drilling, due to surface infrastructure limitations and/or geological constraints," he points out.

The need to achieve multiple intersections of oil-bearing reservoirs through a single 'parent’ drill hole gave birth to the idea of direct drilling. In these scenarios a single 'mother’ hole is drilled, and from this multiple deflections are made in preferred predetermined directions. This results in the intersection of the oil-bearing reservoir at multiple points from the single 'mother’ hole. The production of oil through this single hole is greatly increased.

Costs of drilling in the mineral resources industry have escalated significantly over time. The time taken to drill many holes from the surface down to an ore body in the traditional way also frequently has an effect on the advancement of projects along their timelines. Various players in the industry began to look at the possibility of employing directional drilling technology to achieve multiple intersections on an ore body through a single mother hole.

"Variability of ore bodies in terms of their geological geometry and structure has led to the need to be able to target, in three dimensions, the intersection of an ore body or reservoir from the surface at a reasonably accurate position," Bevelander notes. The planning of the points of intersection with the ore body is based on the structural geology and geostatistics of the ore body.

He explains that the first step is to drill a mother hole from the surface down. If the geology is problematic, the lithology must be traversed in a planned and engineered fashion. Once the hole is of the correct dimension, a down-hole motor with an appropriate diamond cutting head is lowered down the mother hole and can begin to start drilling a hole which deflects out of it.

"The objective is, in a pre-planned way, to aim the deflection in three dimensions out of the mother hole towards the geographic point that one needs to intersect. Once the deflection is completed, the directional drilling equipment is removed from the hole and classical core cutting technology is used to traverse the lithology," he says.

Continual further directional drilling is done in increments, taking the hole in the preferred direction. A section of drilling is done, the equipment is removed from the hole, and a down-hole survey is carried out to confirm that drilling is progressing in the correct direction. The next section of drilling is then carried out in the same way.

"Both the technology itself and the incremental steps in which drilling takes place, are governed by the technical and design capability of the down-hole motors used," Bevelander points out. Generally speaking, the drilling equipment is able to adjust to an inclination in the order of three to five degrees in each sequential step. In this manner a gentle arc is systematically created in order for drilling to progress in the preferred direction.

"It requires a thorough understanding of both the local prevalent geology, drilling technology and the objective in order to apply the directional drilling technology correctly, and teams need to consist of top quality, trained and experienced people," he says.

"With this technology, we are able to provide the client with a single surface drilling platform, and navigate a way towards achieving a drilling pattern which supports the project in its feasibility determination from a geological and statistical point of view," he continues.

Murray & Roberts Cementation is one of the first companies to carry out down the hole motor directional drilling down to approximately 3 000 metres below surface. The company is currently using the technology on a gold exploration project for AngloGold Ashanti in Ghana’s Ashanti province. Two drilling rigs are employed on the project, and drilling is planned to reach approximately 2 500 metre depth below surface.

Directional drilling technology is still in its early stages of development as far as hard rock and deep exploration environments are concerned. It has been used very successfully in applications such as coal and petroleum exploration because of the "softer nature of the geology".

Bevelander comments that there is an expectation in the exploration industry that deep level exploration worldwide will increase, especially if commodity prices continue to be as favourable as they have been. To this end, Murray & Roberts Cementation has made it part of the company’s strategy and vision to develop and maintain its ability in this field.

The main benefits for the client are the time and cost saving aspects, as well as the fact it is possible to achieve multiple intersections from a single hole at the surface. It is possible to achieve meaningful time and cost savings.

"The benefits to the industry include the facts that it is possible to save costs on exploration budgets, improve project time lines and to save time on achieving the required number of intersections on a particular ore body, thereby adding significantly to achieving acceptable feasibility confidence levels in good time," Bevelander states.

"In other words, it is possible to optimise exploration costing and planning, and the technology supports the achievement of a geostatistically acceptable pattern of intersection in order to timeously increase confidence levels to the geological model of an ore body," he concludes.