The World According to Wayne: Solids Control Systems Come of Age
May 3, 2008
The drilling industry never ceases to amaze me. I’ve been around long enough to see some absolutely amazing developments as the industry matures and progresses. I broke out on cable-tool rigs, and we were lucky to make one house well a week – if they weren’t too deep. On deep jobs, such as oil wells, two a year was doing pretty good. Then, kelly-drive rotaries started showing up in the field. They’d been around for a while, but a lot of drillers didn’t trust them. They said they drilled too fast and missed the thin “stringers” that might be the only production (either oil or water) in some areas. That probably was true in the early days, before drillers got the feel of the rig and the bit. We found out that a good driller easily can feel a 6-inch drilling break if he’s paying attention. Then came tophead rigs. At first, they were underpowered and complicated, and tripped pipe at the speed of a glacier. It took the industry a while to get used to them, and for the manufacturers to get the productivity up to promised levels.
One interesting note about tophead technology: Most of the advances in the water well industry have come from the oilfield – rotary rigs, logging, solids control, mud chemistry, that sort of thing. But, the development of tophead drives seems to have originated in the water well and mineral exploration industries, and gradually transferred to the ’patch. The new oilfield topheads are big as a freight car, and do everything but make microwave popcorn. They also can cost more than three or four big water well rigs.
The latest development that has long been needed, but just now is coming into wide acceptance is solids control. Drillers are starting to see the need and the economy of good mud systems, and the market is starting to fill that need. As with a lot of our technology, solids control originated in the oilfield, and gradually is trickling down to the water well industry. As with all new things, there is a learning curve for water well drillers to get up to speed. Hey, it took me quite a while to retire that old 22W and get my first rotary!
Unfortunately, some of the manufacturers are taking advantage of this learning curve to market products that don’t perform as advertised.
A properly sized mud system must be able to process at least 100 percent of the mud that circulates though the hole. This means that it must not only be able to scalp the large cuttings from the mud, it also must be able to desand the entire flow to properly keep up.
I see systems with an advertised throughput of 500 gpm that only have two desander cones on them. Let me explain something: A single, standard API 5-inch cone only will process 80 gpm. This means that two cones will process 160 gpm, period. You may be able to scalp 500 gpm, but if it is not properly desanded before returning to the hole, you haven’t cleaned the mud, and the sand content and weight are going to go up, way up. Pretty soon, the mud will be out of control and have to be pumped off and replaced, negating the reason to have a mud system in the first place. This works OK on small wells that take only a few hours to drill; you are going to pump off anyway. But if you are on a larger project, such as a geothermal drilling job or larger, deeper commercial projects that require the same mud to be used day after day, you are going to find yourself circulating liquid emery cloth. Not good for the pump or the hole.
Remember this: A high-school kid with a shovel can take out the big cuttings, but it takes the right equipment, in the right size to take out the fines, and this is the difference in a well-designed mud system. Next time you look at a mud system, ask the salesman how many gallons a minute the system is designed for, then simply count the cones, and multiply by 80. If those figures don’t add up, I’d walk away.
Another thing to look at when considering a mud system is the shaker. Things to look at are screen type and basket motion. Screens come in a bewildering array of mesh sizes and shapes, but the critical aspect is the attachment method. The older-style hook-strip screens are a little cheaper, but they have some problems. They take a lot of time to change, and they must be retensioned periodically. If the crew isn’t on top of things (like they don’t have enough to do already), the screens will be either too tight or too loose most of the time. This leads to much shortened screen life, making cheaper screens a joke when you consider initial cost and downtime to replace them – if you have spares on hand. The more modern screens are pre-tensioned; they are built on a sub frame that slides into the shaker basket, and are secured with wedges. With 30 seconds and a 3-pound hammer, you can change a screen and be back on line. The tension is factory-set, and never needs adjustment.
Next, look at the motion of the basket. Obviously, the basket must vibrate to separate the cuttings from the mud, and the shape of the vibration is critical to the efficient operation of the shaker. Most shakers operate with orbital, elliptical or linear motion. The original oilfield shakers all were orbital. In other words, the motion of the basket was a small, round circle that forced the mud through the screen, and required a pretty good downhill slope to transport the cuttings. The advantage is that they are cheap. The downside: They will not handle much of a polymer load. No matter what the salesman says. They generally will blind within minutes. Their solution to this is to run screens with such a large mesh that they don’t do much, except take out the big chunks (and throw the load on already undersized desander circuits). The modern solution to this problem was the development of linear shakers. The actual motion of the basket is in a straight line, at a 45-degree angle to the discharge end. A linear shaker not only will handle significantly more throughput, it also will handle polymer loads that will choke an orbital shaker in minutes. Since it can handle more throughput, finer screens can be run, increasing the efficiency of the desander circuit.
These are some of the features to look at when considering a mud system. There are a lot of others, but the shaker/mud cleaner is the heart of the system, and the part that does the work. You probably can get a cheap system, but that’s just what it will be – a cheap system. Your mud, pump and hole will know the difference. And so will your wallet after a while.
On a side note: As many of you know, I’ve been building solids-control systems for years now. I recently have had to move my fabrication facilities, due to theft and mismanagement issues, and now it seems that these people have decided to steal my designs and build knock-offs of my equipment. Let the buyer beware: If you aren’t talking to me personally, you are not getting ProDrill Systems equipment and may be dealing with people who never have drilled a foot of hole – and who not only will steal from their employer, but most likely will steal from their customers as well.