Most of us in the water well industry know our areas well enough to be able to preplan a well and go to the location with the right tools and equipment. But sometimes Mother Nature, or geology, fools us into problems. Knowing what to expect sure helps, but sometimes we run into the unexpected. Murphy’s Law throws a curve. At depth, we can’t see the bit any better than a blind man could. We have to use the surface clues and indicators we have to complete the well.
The most common problem is when we drill a shallow, low pressure zone knowing the productive formation is deeper, and we have to control it to get there. The lower formation may be pressured up, meaning we may have a flowing well on completion. This requires mud with a higher specific gravity than the shallow formation will stand. In this case, good mud is a must. The specific gravity of the mud must be low enough to not lose mud in the upper, low pressure formation, and still hold the higher pressure formation back until you have finished the well. Mud that builds a good, thin, tough wall cake is key. Natural clays won’t do this, so you will need some thoroughly mixed — and properly hydrated — bentonite mud with area-specific additives.