Prime Horizontal Ltd, a pioneer in developing intersection technology for the horizontal directional drilling (HDD) industry, is now servicing the coal seam gas (CSG) market with the equipment and engineers to perform horizontal-to-vertical well intersections.

The company's Rotating Magnet Ranging System is being used to guide, in real time, the drilling of CSG production wells when they are drilled horizontally to intersect vertical production wells.

To improve production and allow better flow and dewatering of CSG wells, it is common to have at least one vertical well intersecting the horizontal lateral. Pumps are located in these vertical wells to remove water as well as to lift the gas to the surface. The technique used to intersect these vertical wells is important, as issues with poor intersections can include build-up of coal fines in the vertical well and problems with the water flowing towards the intersection point.

In this application, using a rotating magnet, a steering tool is lowered into the target well while a magnet sub is located in the bottom hole assembly (BHA) directly behind the bit of the horizontal well. The rotation of the magnet sub generates an alternating magnetic field, which is measured with the sensors in the steering tool. As the horizontal drilling comes into proximity of the target well, the magnetic fields are recorded and processed with the output information being co-ordinate range and angular co-ordinates to the target well. The result of the process is the intersection of the vertical target well by the horizontal well by means of correcting the original trajectory using the ranging information from the Rotating Magnet. It is now possible to intersect the target without having to perform a sidetrack and re-drilling as is currently required by DC and Passive ranging technology.

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The use of DC magnetic fields for ranging of vertical well targets is well documented and has been used for a number of years in the CSG industry. Not so well known are the technical benefits gained when using AC magnetic fields rather than DC fields. The primary benefit of using AC rotating magnets is the increased signal-to-noise ratio against the various magnetic distortions commonly encountered in HDD magnetic guidance. In a magnetically quiet environment, DC magnetic fields work well, but the more common case is a magnetically noisy environment in which magnetic field distortions have one or more causes. In these environments, the sensitivity of the steering tool to common AC magnetic field distortions is reduced by the use of the AC Rotating Magnet in combination with appropriate noise reduction software so ranging can be performed with greater confidence.

There are numerous economic benefits for using Prime Horizontal’s rotating magnet ranging service. Intersect operations become streamlined and take less time. This in turn allows better planning for operators to gain cost savings from their production plans. Well conditioning is maintained and the risk of losing horizontal drilling tools downhole while ranging at depth is reduced since, while ranging, the circulation is maintained constant, whereas DC ranging requires the pumps to be turned off each time a co-ordinate ranging “shot” is taken. Ranging occurs while the well is being drilled, so the only time necessary to halt drilling operations is the time needed for the regular breaks to connect drill pipe and take directional surveys.

By using the AC magnetic technology, Prime Horizontal now offers a unique service that is at the forefront of technology in completing more productive CSG wells.