Problems with Boulders

Problems with Boulders

The most significant challenge for drilling contractors is dealing with boulders. In reverse circulation well drilling, boulders remain the most difficult type of deposit to penetrate. Depending on their size and placement, they can cause various problems, from blocking the drill rod and pump to forcing complete abandonment of the reverse rotary method. In extreme cases, it becomes necessary to use a large cable tool rig to drive the casing through the boulder zone before continuing with reverse rotary drilling. Sometimes, both types of equipment must be available, alternating drilling methods to complete a well successfully.

Regardless of the depth reached or the diameter of the well, all wells are designed to be drilled in one of two ways: as a straight, full-diameter hole to the bottom or as an under-reamed hole. Straight-diameter holes are typically faster to drill and are suitable for wells with single casing. Under-reamed holes are generally required when a well has double casing and the outer casing is cemented into place above the screen zone.