The World According to Wayne: Well Abandonment in Hard-rock Formations
The
purpose of proper well abandonment goes far beyond just covering it up so your
horse won’t trip in it. The purpose is to restore the geologic conditions to as
close as possible to original before the well was drilled. To do this properly
sometimes takes more steps and engineering than the local government hand has
written down in his complete book of instructions. You could follow his
instructions, but you might not make a proper abandonment, or it might not be
doable. In this case, negotiation and education is the key.
Well abandonment in hard-rock aquifers where the production is from large fractures, vugs or sometimes extensive caverns is particularly challenging. Historically, the most common abandonment material is neat cement. This is cheap, available and accepted by most bureaucrats, but it won’t always work without some “enhancement.”
One of the first steps is to know what you’re dealing with. Good well logs may or may not be available, but if they are, they’re a start. From the log, you can calculate approximate well-bore volumes to figure your cement. If logs are not available, sounding or logging and some knowledge of the local geology will help. Now we get to the tricky part: Since cement has a much higher specific gravity than water, when pumped in a well, it may overcome the natural formation pressure, and leak into the formation faster than you can pump it. In vugged formations, this sometimes can be overcome by adding gel to the cement to 1) lighten the hydrostatic head, and 2) increase the viscosity of the mix. This will allow it to stay where you put it until it sets and develops enough mechanical strength to stay where you need it.
If the formation is highly vugged, fractured or cavernous, a different method usually is employed. Since the formation usually won’t take much hydrostatic pressure, pumping a huge column of cement is impractical, as it will leak away. If lightening the hydrostatic head with gel is not enough, staged cement may be the answer. This is done by pumping small amounts of cement (a few sacks) at a time, and letting it develop some compressive strength before the next stage. This may take a long time, and if you anticipate this condition, be sure to figure it in your bid; you may be there for a while. I’ve seen wells that took more than a month to properly cement. In states that require an onsite witness to all abandonment procedures, this will make you very popular with your inspector if you pump 20 sacks, wait 3 hours, pump 20 more sacks, wait 3 more hours until you have the entire 1,200 sacks in the hole.
One way to cut the WOC (waiting on cement) time is to accelerate the cement. One of the most common methods: calcium chloride. This will cut the waiting time considerably, depending on how much you add, but be careful, too much and the cement will flash-set in your pumps and tremie, and ruin your day. If you see the pressure start to spike, and the pump is grunting and groaning, it’s time to do something right now. An old trick that still works is to have 10 pounds or so of sugar on hand. Sugar will prevent cement from setting for a good, long time, long enough to wash out your pumps and save the job, if not your tremie line. Just add it to the pump suction, and let it work. If you don’t use it, you always can take it home for your wife to use to make tea.
If the hole is so fractured or cavernous that staging cement is not practical, there are other methods. One of the purposes of proper abandonment is to restore the hole to pristine condition geologically. This means sealing any interconnection between discrete, separate aquifers. If the section you are sealing is all one aquifer, sometimes it is acceptable to pump gravel of the same formation as native. This works well and is fast, but is not always allowed by the regulations. If not, bentonite chips – if allowed – are an alternative. They are more expensive, but the make an excellent seal between aquifers. If you are dumping or pumping them deep, it is important to screen out the fines, or they will swell before you get them where you need them. Additional pump/dump time can be gained by mixing some polymer such as Baroid E-Z mud (usual disclaimer) to the mix water.
Once you have cemented up to the casing shoe, it is easy to calculate the displacement and pump to surface in one batch. Allow enough excess for your inspector to see, and you are almost done. Keep in mind that cement is at its greatest volume when it is pumped, and will shrink. When you go back the next day, don’t be surprised if the cement level is down somewhat; this is natural. Actually, it’s probably a good thing. It allows you to cut off the casing below ground level, and fill to surface so your horse won’t fall in it.
Hope this helps. If you need any help abandoning a well or with general cementing, give me a call.
Just in case ya’ll think I’ve gotten all serious or something, I’ve got to tell you a story about my brother Willard. Ya’ll know my brother Willard; he’s not the sharpest bit at the rig, but he likes to go moose-hunting in Alaska. He’s been a couple times and done pretty well, too.
Last year, he went to a little camp on Lake Whodathunkit. Hired a plane out of the Yellow Pages. I guess he didn’t understand exactly what “bush pilot” meant. The pilot delivered him and his gear, and he had a wonderful week and shot a good-sized moose. After a few days, the pilot showed back up to get him, and Willard started loading a 1,400-pound moose in the little ol’ single engine plane. The pilot told him that the moose was too heavy, and he couldn’t take all of it: “You can take the head to mount, or a haunch to eat, but not all of it.”
Willard told him, “I kill’t a moose last year, and the pilot let me put in the plane. It’s about the same size as yours.” The pilot finally gave in, and they loaded the moose and all Willard’s gear. The plane roared, struggled mightily to take off, but didn’t quite clear the tree line on the other side of the lake. Down they went. The crash pretty much destroyed the plane and knocked out the pilot. Willard wasn’t hurt – probably because he was drunk – and got out to check the damage; it was totaled. About that time the pilot came to, and asked Willard, “Where are we?” Willard said, “’Bout a 100 feet farther than we made it last year.”
ND
Well abandonment in hard-rock aquifers where the production is from large fractures, vugs or sometimes extensive caverns is particularly challenging. Historically, the most common abandonment material is neat cement. This is cheap, available and accepted by most bureaucrats, but it won’t always work without some “enhancement.”
One of the first steps is to know what you’re dealing with. Good well logs may or may not be available, but if they are, they’re a start. From the log, you can calculate approximate well-bore volumes to figure your cement. If logs are not available, sounding or logging and some knowledge of the local geology will help. Now we get to the tricky part: Since cement has a much higher specific gravity than water, when pumped in a well, it may overcome the natural formation pressure, and leak into the formation faster than you can pump it. In vugged formations, this sometimes can be overcome by adding gel to the cement to 1) lighten the hydrostatic head, and 2) increase the viscosity of the mix. This will allow it to stay where you put it until it sets and develops enough mechanical strength to stay where you need it.
If the formation is highly vugged, fractured or cavernous, a different method usually is employed. Since the formation usually won’t take much hydrostatic pressure, pumping a huge column of cement is impractical, as it will leak away. If lightening the hydrostatic head with gel is not enough, staged cement may be the answer. This is done by pumping small amounts of cement (a few sacks) at a time, and letting it develop some compressive strength before the next stage. This may take a long time, and if you anticipate this condition, be sure to figure it in your bid; you may be there for a while. I’ve seen wells that took more than a month to properly cement. In states that require an onsite witness to all abandonment procedures, this will make you very popular with your inspector if you pump 20 sacks, wait 3 hours, pump 20 more sacks, wait 3 more hours until you have the entire 1,200 sacks in the hole.
One way to cut the WOC (waiting on cement) time is to accelerate the cement. One of the most common methods: calcium chloride. This will cut the waiting time considerably, depending on how much you add, but be careful, too much and the cement will flash-set in your pumps and tremie, and ruin your day. If you see the pressure start to spike, and the pump is grunting and groaning, it’s time to do something right now. An old trick that still works is to have 10 pounds or so of sugar on hand. Sugar will prevent cement from setting for a good, long time, long enough to wash out your pumps and save the job, if not your tremie line. Just add it to the pump suction, and let it work. If you don’t use it, you always can take it home for your wife to use to make tea.
If the hole is so fractured or cavernous that staging cement is not practical, there are other methods. One of the purposes of proper abandonment is to restore the hole to pristine condition geologically. This means sealing any interconnection between discrete, separate aquifers. If the section you are sealing is all one aquifer, sometimes it is acceptable to pump gravel of the same formation as native. This works well and is fast, but is not always allowed by the regulations. If not, bentonite chips – if allowed – are an alternative. They are more expensive, but the make an excellent seal between aquifers. If you are dumping or pumping them deep, it is important to screen out the fines, or they will swell before you get them where you need them. Additional pump/dump time can be gained by mixing some polymer such as Baroid E-Z mud (usual disclaimer) to the mix water.
Once you have cemented up to the casing shoe, it is easy to calculate the displacement and pump to surface in one batch. Allow enough excess for your inspector to see, and you are almost done. Keep in mind that cement is at its greatest volume when it is pumped, and will shrink. When you go back the next day, don’t be surprised if the cement level is down somewhat; this is natural. Actually, it’s probably a good thing. It allows you to cut off the casing below ground level, and fill to surface so your horse won’t fall in it.
Hope this helps. If you need any help abandoning a well or with general cementing, give me a call.
Just in case ya’ll think I’ve gotten all serious or something, I’ve got to tell you a story about my brother Willard. Ya’ll know my brother Willard; he’s not the sharpest bit at the rig, but he likes to go moose-hunting in Alaska. He’s been a couple times and done pretty well, too.
Last year, he went to a little camp on Lake Whodathunkit. Hired a plane out of the Yellow Pages. I guess he didn’t understand exactly what “bush pilot” meant. The pilot delivered him and his gear, and he had a wonderful week and shot a good-sized moose. After a few days, the pilot showed back up to get him, and Willard started loading a 1,400-pound moose in the little ol’ single engine plane. The pilot told him that the moose was too heavy, and he couldn’t take all of it: “You can take the head to mount, or a haunch to eat, but not all of it.”
Willard told him, “I kill’t a moose last year, and the pilot let me put in the plane. It’s about the same size as yours.” The pilot finally gave in, and they loaded the moose and all Willard’s gear. The plane roared, struggled mightily to take off, but didn’t quite clear the tree line on the other side of the lake. Down they went. The crash pretty much destroyed the plane and knocked out the pilot. Willard wasn’t hurt – probably because he was drunk – and got out to check the damage; it was totaled. About that time the pilot came to, and asked Willard, “Where are we?” Willard said, “’Bout a 100 feet farther than we made it last year.”
ND
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