Borehole surveying

Paul Boughton

Maurice Jones examines the latest developments in borehole surveying

Borehole surveying has had a long history of mainly steady development due largely to the demands of the upstream oil and gas industry where the stakes are high, including the available investment for the right methods. 

National geological surveys have also played their part, with the emphases on ‘pure’ research and the mapping of a state’s mineral and water resources.

Similarly the mining industry is naturally interested in potential reserves, although perhaps on a smaller and more detailed scale. The industry is also interested in using well monitored boreholes to find out about geological structures that may disrupt mining plans, groundwater to be used or avoided, and perhaps voids due to older mine workings and natural processes.

The ever-present pressure on costs means that it is important to reduce the time taken for drilling, monitoring, data collection and analysis of results if possible. Thus cutting the time taken for procedures is a spur to development.

Reflex (Imdex Group) recently introduced a rapid descent version of the Reflex ACT digital core orientation instrumentation package with the ACT III RD. Subject to the condition of the bottom hole assembly it is claimed to be accurate to 88 degrees. It is waterproof and shock-tolerant and is easily maintained.

The drive for rapid data collection to save time and avoid drilling errors can be aided by Measurement While Drilling procedures, also sometimes known as Logging While Drilling (LWD). Much depends on the type of data required, the instrumentation that can be installed in the bottom-hole-assembly of the drill-string, and cross-interference that may occur between system and other drilling equipment. 

Scientific Drilling of the US and worldwide offers MWD services based on the use of mud pulse, electromagnetic and gyro devices. The company emphasises reliability with its TUF (Tool Utilization Factor) system to accumulate data on tool wear based on temperature and vibration levels (directionally logged) down the hole. The customer should then be able to achieve longer drill components life.

Devico of Norway offers a range of borehole logging and instrumentation systems with the emphasis on coring by directional drilling and multi-shot instruments. The use of accurate directional drilling from a single rig set-up can greatly save of exploration time and produce related data across variable-shape orebodies and other deposits from fewer locations. 

The Devico DeviShot multi-shot borehole survey instrument can record inclination, azimuth, too-face position, gravity vector, magnetic field vector and magnetic dip as well as the temperature and battery status. It comes with its own flexible DeviSoft .

Renishaw of the UK produces a number of borehole logging tools including the Boretrack. It is also marketing the C-ALS, which is a laser scanner deployable from a borehole to check on the presence and size of concealed voids to cut out the guesswork when one is encountered by drilling.  It is claimed to be the only such borehole deployable device on the market and is more accurate than alternatives such as ground-penetrating radar.

The processing of data collected, whatever its accuracy, can be a time-consuming and therefore expensive task. EpiLog from K&A Epimetron is an exploratory works management service that allows the user to enter, process and monitor many works in real time via the Internet. 

The main advantages of this procedure are immediate recording and management of drilling data, monitoring of works progress anywhere at any time, automated and immediate computation of quantitative data and a great reduction in the time required to produce reports and other documents. Results include valuable additions to exploratory data, better structural safety for mine workers and more accurate estimation of remedial measure requirements.

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