No matter how carefully you planned and drilled, bore holes are rarely straight. Many things can have an effect on the direction of the hole, such as weight on bit, poorly set up drill rig, fractures or voids in the ground formation, bedding planes, or ground that goes from hard to soft. Too often, the path of the bore hole needs to be corrected in order to reach a desired target and that is when you should consider using a wedge.
There are several different styles of wedges available for different applications. The By-Pass wedge is placed at the bottom of the hole or on top of a cemented section and remains a permanent fixture in the bore hole. However, it can take up to 4 trips in and out of the hole to install this wedge. The Retrievable wedge can be oriented, and removed completely after the deflection is made, leaving no steel in the hole. The Casing wedge is a tool where the corrected hole to be drilled is one size smaller than the parent hole. The wedge facet is installed at any given point in the casing string, which stays in place. Drilling continues in the next smaller size.
My favourite is the One-Trip Wedge system. It allows the driller to lock the wedge securely at any point in the bore hole, orient the wedge, and anchor the facet in the desired direction – all in one trip. This saves a lot of time, thereby increasing productivity.
Regardless of the tool you choose, you should take certain precautions before setting your wedge.
These are 5 precautions you should take to avoid issues:
Make sure the bore hole is clean, free from cuttings and sludge and is stable.
Keep detailed notes of the bore hole, such as the type of ground conditions encountered in the hole, any fractures or voids, etc. Make sure to examine the core to determine the best location to position the wedge
Never place a wedge in badly broken or fractured ground, sandy conditions etc. If the wedge has to be placed in this type of condition, an option would be to cement the hole, wait for it to dry and then re-drill/
Use a suitable lubricant in the circulating water, such as Torqueless™ or a polymer. Good lubrication of your diamond tools will enable the bit to cut into the rock and stay off the steel.
Keep detailed notes, sketches and measured lengths of everything in the hole including the rod string, wedge facet, dropper, adaptors etc. Once the wedge is placed, note the exact location of the top of the wedge in the drill as caution is required on subsequent trips in and out of the hole
While wedging still remains a tricky exercise, technology and driller experience have allowed manufacturers to improve on existing options. It can be wise to check with a manufacturer’s technical support team for advice and to tap into their combined experience.