The End In Mind
Originally written for the NGWA toolkit
So, there we are, myself and the driller Shifty. Shifty is telling me he just can’t figure out why this well isn’t performing the way it did when it was built. I asked Shifty what was wrong with the well? His reply was that it was “heavy on sand, light on flow”. I absolutely love specific details, precise units of measure, accurate field measurements. Shifty makes me want to turn into oncoming traffic sometimes.
I tried again “So, more sand and less flow, right? Any idea how much more, and less?” Shifty realigns with the celestial drilling crystal, and replies “Well, more or less too much and not enough, according to owner”. If there were a bridge near, I’d jump.
“Shifty, when was the well constructed, and what kind of perforations?” Chin scratching, removal of the 14-year-old ball cap, and then I get this reply “About 35 years ago, and we torched a bunch of them into the pipe, for about 400 feet”. I’m done, send me home Coach.
Future historians will hold me accountable for this, and there is no good reason for what I was about to do, but I asked one more question. “Shifty, when was the last time you pulled any maintenance on this well?”. Stunned silence, its so quiet I can hear the cedar waxwings migrating. “Well, as best as I can remember, never”. I have nothing.
So, the moral of this story? Well, there are several, but let’s focus on one. I believe that it’s best to design and build wells with the end in mind. And that end is a long and effective operational life for a well, which is an asset to the owner in this paradigm, that serves it purpose well.
Reverse engineering this scenario, wells need to be built so that they can be maintained. We’ve learned that lesson over the last 20 years or so, and we seem to be getting a little better at maintaining them. However, when many wells were built, there was little to no thought given to well maintenance, or rehabilitation. A well fails, you drill a new one, that’s the way it works.
Wells are “a subsurface hydraulic structure” and like other structures, they need to be maintained. Many bridges have no moving parts, and yet they do in fact need to be maintained, lest they fall down on someone. As such, keeping in mind that structures need to be maintained, we need to design wells to perform adequately over the entire operational life of the well. This means, wells that can both provide water effectively and efficiently, when pumped; and wells that can be maintained.
Well maintenance is more then brushing and blowing bubbles into a well. Perhaps the most critical component of effective well maintenance, is the ability to cause fluid movement through the intake structure (i.e. well screen, perforations, slots, etc.) at rates sufficient enough to move water through the filter pack. And the rate that fluids need to flow, should not be so low as to “just” move water, and on the other end, not so high as to create a water-jet cutting effect that damages well casing or intake structures.
With that in mind, then the design of the well needs to take into consideration the type of intake structure, and the thickness of the filter pack surrounding the intake structure. The design needs to facilitate maintenance. There are existing vehicles, that have such compact and crowded engine compartments, that to change the oil, requires almost removing the engine! We do not need wells like that. We need wells that are hydraulically efficient structures, that can be easily maintained.
Intake structures that are of irregular size and shape, that provide too little access to the filter pack, and that are too easy to plug, reduce the effectiveness of well maintenance. Intake structures need to be strong, and allow water to easily flow into the well. However, these same intake structures need to allow water to flow out, often under pressure, as part of a maintenance program that includes flushing the filter pack. This is initially critical in well efficiency development, i.e. well development. And it is also critical in the long-term maintenance of the hydraulic efficiency of the filter pack – intake structure couplet.
Filter pack thickness, is both a design and construction concern, and challenge. Well designers want thin filter packs, for hydraulic efficiency and ease of development and maintenance. Well contractors would like to oblige, but properly installing a well usually requires at least three inches of room between the casing and the borehole, the space called the annulus.
State and local agencies, along with various engineering organizations, all have suggestions, and sometimes requirements, for gravel pack thicknesses, minimums and maximums. Following both these requirements and good construction practices, gravel packs tend to nudge up there because it’s easier and less problematic for the installation of the gravel pack.
The thicker the gravel pack, the more time, energy and money it is going to take to properly develop the initial well efficiency. Over time, through the life of the well, a thicker gravel pack will more then likely create conditions where maintenance and possibly rehabilitation, become more costly compared to a thinner gravel pack, simply because keeping the gravel pack relative free of clogs, debris and the occasional sand trout is more difficult.
Back to Shifty. He built a well, cheap and fast, and for the first few years his client was okay with the well. But then, it started to pump sand, enough to damage two pumps. Then, it started to experience a decline in flow rate. Shifty did nothing, just shrugged and said “That’s a well for you. Want a new one?”. Finally, when his client needed water, and hand mostly wet sand coming out of the well, Shifty had to take action. Had Shifty built this well, with his clients best interests in mind, Shifty would have made it easy to maintain, and provided that service to his client, and made some well earned profit for his efforts.
In the end, Shifty pumped the old well full of concrete, and drilled his client a new well. Now, I wish I could tell you that one or the other of them, Shifty or the client, had decided to invest in a better well, but sadly, no they did not. I was fortunately not present, having already found a bridge nearby if they had asked me to help them.
What did we learn? Design and build wells that can be maintained. Pretty simple, keep the end in mind, make things that can last, focus on craftsmenship.