When I drilled this little well over 30 years ago the little sand at 1,781 feet was clean looking on the open hole logs and upthrown on the controlling field fault. I'd never seen it before drilling in the trend; it just popped out of nowhere, a depositional fluke of nature. I shot a sidewall core in it, just for fun.
When the core analysis was mailed to the office, the permeability in this sand was OK, the gas by volume was low, however, and total water was too high, by my way of thinking. The cased hole gamma ray/neutron log had a small neutron response indicative of gas. It was not a big deal and I forgot about it.
We produced the well for seven years in lower oil zones below 2,000 feet; the well paid out with something a little less than a disappointing, 200% ROI. This was a low, flank well at or near oil-water contacts and it was time to plug the damn thing. I went thru the well file one least time (SOP in my shop) and there was this little tiny sliver of a sand left to try. Gas prices were pretty good back then. So, what the hell...
I set a cast iron bridge plug at 1,850 feet, bailed 20 feet of cement on top of that. Ran a production packer to 1,680 feet, loaded the back side and tested, broke the tbng. collar out and spun a 2000 PSI F/O valve on it and shot the well with thru-tubing Link (Tornado) jets, 2 feet, 2 SPF. That all cost about $5,500 including rig time and perforating.
I had immediate pressure at the surface and the CCL and rope socket blew up the hole as fast as we could reel it in. It hit the lubricator pack off with a big... whap! The head would not squeeze off very well and the well started hissing gas and water. It surprised the shit out of me and the logging hands were scared of it. I led them in, we closed the master valve, rigged all their crap down and sent them to the house.
I scrambled around looking for more 2000 PSI fittings and as much Teflon tape as I could find, nippled up a nominal choke body, stuck a 10 in it, staked down a flowback line, and opened 'er up. It unloaded kill fluid in about 8 minutes and the damn FTP kept going up and up and up. I said to one of the rig hands, "well, lookit this son of a bitch, will ya?'
When I lit the flare it 'bout knocked my hard hat off and the FTP keep climbing. After 3 hours of testing I was sufficiently impressed.
I calculated probable recoverable reserves based on volumetric GIP and spent another $10K hooking the well up to a nearby low pressure gas line. I was going to be tickled plum to death with 150% ROI on plugback and hookup costs, based entirely on net sand thickness of 3.0 feet. I started producing the well on a 5 at about 780 PSI FTP.
Well, it was like I popped holes in a pipeline. The well produced for 12.5 years and made over 321 MMCF of dry gas, no water, net to the 100% working interest owners, myself included. The ROI on the plugback was 4,287% and ROI on the entire well ultimately ended up nearly 625%. For a few months I started to think of myself as a real oil man, then drilled two straight dry holes and got over that shit real quick.
I never saw this little sand again in any subsequent infill, or exploratory wells drilled in the entire trend over the next 25 years. It was a simple gift from the Goddess, Eocene.
It just goes to show you, always have one last look at your well files before calling the funeral parlor... and leave no stone unturned.
Every now and then there might be a pleasant surprise under it.