All's Well That Ends...Properly Cemented
How did it all go so wrong?
It's the day before. We're out in the Texan countryside, enjoying the 100+ heat index and watching roadrunners dance by the drill rig (such cute little guys!). I've expertly navigated the field truck around the mesquite thorn trees...well truthfully, we didn't get a flat tire so I'd call that expert-level.We've been here a while, drilling a 700 ft deep test well for groundwater supply. We've drilled the borehole, threaded together all the screen and casing (10 inch, ductile iron), filled around the screen with a filter pack (sand to marry the new casing to the geology), completed geophysical downhole testing, and are waiting on the cement truck to finish filling in the annulus with cement.For a good amount of the time we spent waiting for the cement truck, I'd sat in my field truck meticulously calculating the exact amount of cement and water needed to meet the design specifications from the design engineer. (I can show you my spreadsheet if you want to see it...it's pretty AND helpful :lol: ). 367.01 cubic feet. Give or take some allowance for potential voids in the ground that might be filled with grout during the cementing process.
Two semi-sized trucks, one water truck, and a super duty american-made service truck rolls up onto the ranch. For some reason, the driller subcontracted an oil well grouting company instead of one of those big rounded-belly ones you see at construction sites. Four very young, very well dressed oil field cement grouters step out of the trucks. These guys got paid well, were attractive, and knew it. What they didn't know was how much cement they put into a well. My calculations would not be needed.To be fair, the well we drilled is extremely tiny by oil field standards so their metrics are for much bigger amounts of cement. They pump it into the annulus starting at 470 feet below the surface (the purpose of the cement is to protect the drinking water aquifer from cross-aquifer contamination via the well) until it comes out on the ground. The cement is left to set all night.We wrap up and trek home. It's now after midnight.
The next groggy day, we get a call from the drillers. They were out on site doing finishing touches and measuring depth to water in the well. They had dropped the water level meter into the well.... 10 ft... 20 ft... 30 ft...it keeps unwinding... 39 ft.... and hits cement. Inside the well. The entire well was cemented up to 40 ft below ground surface.We're certainly not pumping groundwater out of that well.
How did it all go so wrong?
There's a couple of possibilities.
It's possible that the casing threading was not completely together--either leaving space for cement to get into the well or dropping off the bottom completely.
While inserting the casing into the well, the iron may have been punctured by a rock at the edge of the borehole.
The casing got sheared apart downhole while the rig was lowering it into the hole.
The filter pack and clay plug filled up a void in the bottom of the hole and didn't completely cover the screen, allowing cement in through the screen.
And any other number of possibilities. We speculated for days and days and days. We became detectives that week!
So the drillers got back out there a couple of weeks later and drilled a whole new well. 700 ft deep. I'm guessing in the ballpark of $100,000. Whatever happened, that was an expensive mistake. They performed the pumping tests and concluded that the area was suitable for a production well. Next week, I will be finishing up finalizing the specifications and drawings for the production well that will be drilled here.All's well that ends well.
Reading: Britt-Marie Was Here. Fredrik Bachman. I read his "My Grandmother Told Me to Tell You She's Sorry" and loved it. Excited to read his new one about a character from the other book.Listening: Planet Money podcasts - I found myself a few weeks behind!Working: Groundwater production well specifications, finishing up a 100% submittal for a wastewater conveyance project, and wrapping up the tech memos for the confidential project from last week.