Higgs, in south Louisiana, the rig is set up over the area where the well is to be drilled. Before the well is drilled they set a string of drive pipe. It is usually 24" OD. They pick it up in 40 foot joints with a hydraulic hammer above it. It is then run thru the floor down to the to the ground and hammered down into the soil. They will continue to pick up joints of drive pipe and weld them together and drive them into the ground until it takes between 20 to 25 hits in order to drive it one foot. In some areas you may be able to drive to pipe as much as 300 feet deep. This drive pipe is very heavy about 125 lb/ft and about 1 to 1 1/2 inches thick. The well is then drilled and several other casings are run at different depths and cemented in the hole. If the well is abandoned sometimes the operator (oil company) will try to recover the casing that has been cemented to use on another well. The casings are then cut off above the cement tops and laid down. The drive pipe stays in the hole. The rig sets several plugs as per the Louisiana oil and gas commission. The plug they do not set is the top or last plug. The rig is then moved off. A lease crew along with a track hoe come in and they usually dig down 15' below ground level and cut off the drive pipe. The drive pipe and the 10' or so are filled with cement. Dirt is then used to finish covering up the hole. Sometimes the operator decides not to recover the casing and plugs are set in the last casing that was set and the rig moves off. The lease crew and track hoe comes in and digs down cuts off all the casings and the drive pipe level with each other below the surface. Then the cement is placed in the last string of casing and the hole is covered the same way. There has been instances where the drive pipe will start to settle and slowly drop deeper in the ground, especially after time. If the other casings were cut out and laid down then their tops would not be up at that 15' level. If the other casings were still in place then only the drive pipe would settle and the casing would be viewable.
Cache, if you continue to dig make sure that whoever goes into that hole is tied off. Just in case someone is in the hole and standing over what could possibly be 24" OD drive pipe there may not be much of a cement cap inside that drive pipe and it would be a bad day if someone was to fall in. I hope I am wrong and you find some burried treasure. I also have a Gemini 3 and I have located 3" pipes at 10' deep. Good luck.
