Solids Control — Part 1
The benefits of a good solids control system are many and contribute to your bottom line. Benefits to the borehole include thinner wallcake. This means lower circulating pressure and less horsepower required for the pump as well as less chance of differential, or wall sticking — meaning you can more easily and quickly trip pipe without swabbing the hole in. Next is faster penetration. We all know that the faster you can drill, the faster you can cash the check. Good solids control allows faster penetration because you don’t have to regrind the cuttings. It took a lot of time, effort, money, labor and bits to get the cuttings to the surface; there is no point in circulating them around again. Besides, bits are not a cost-effective way to make large cuttings into small ones! Control of hydrostatic pressure also is a consideration. High-solids mud exerts higher hydrostatic head on the formation. If you are drilling a loose, low-pressure sand, the last thing you want for mud is some kind of 15 pound-per-gallon yogurt-looking mud knocking the bottom out of your hole.
When the hole has reached total depth (t.d.), and you trip the drill pipe out of the hole, it’s time to run casing. Good solids control during drilling and a good, thin, tough wallcake will allow much easier casing insertion. A thinner, slicker wallcake will allow you to drill a smaller hole and still get the casing in. With proper solids control, gravel packs are easier to insert and develop, and grout seals better because you don’t have to fight the solids left in the hole to make a seal.
There is another important benefit to good solids control — the mechanical benefit. Abrasive solids wear out things. Emery cloth is made up of many small, sharp solids. You never sand your ‘57 Chevy with a brick, you sand it with fine grit emery cloth. This is the same with rig parts. Actually, large solids do less damage than small ones. It is the continuous, fine blasting effect that wears out your rig. Consider the mud pump: A slurry of fine to medium quartzite sand continuously circulating through the pump will drill OK for a while, but it will wear out the pump swabs, liners, rods and valves quicker’n Bill Clinton can tell a lie. When you have to rebuild the pump prematurely, you are wasting money that should be on your bottom line. In addition to the parts for a rebuild, add the fact that it probably will take a couple of pretty good hands better than a half day to rebuild the fluid end of a typical pump. Good hands cost money and could be put to better use making hole.
In addition to the pump, mud and the solids it contains impact other parts of the rig as well. Often overlooked until too late is the impact of high-solids mud on the swivel. Most swivels have a smaller bore than the hose leading to them or the drill pipe. To pump a given amount of fluid through a smaller cross section, higher velocity is necessary. This increases erosion tremendously in high-solids mud. After the swivel, the mud must pass through the drill pipe. High-solids mud can scour the interior of the drill pipe to failure. Most drill pipe is made to take quite a bit of exterior wear before failure, but interior wear is harder to detect and allow for.
After the drill pipe, the mud flows through the bit, where it really starts doing its job. In case you haven’t won the lottery lately, you’ve probably noticed that bits cost money — real money. We all try to get as much footage out of our bits as possible, but a high-solids mud will eat bits like a bunch of termites on an old pine house. My friend, Richy, only got about 800 feet out of a bit I can usually get 3,000 feet out of. The reason? His mud looked like liquid emery cloth.
Now that I’ve got you all scared as a bride with a cold sore, let’s look at the historical methods of solids control.
The easy — and some drillers still think — cheapest way to control solids is to dig a pit in the customer’s yard. This fairly low-tech approach has worked for years and actually works pretty well if properly done. The first consideration is pit size. It needs to be at least twice the capacity of the hole. The reason for this is that you must contain all the cuttings from the hole and still have enough room left over for proper treatment and volume. I seldom see a house where the well driller has dug a pit this size. The pit should be a two-part pit — with the first part large enough to contain the cuttings and the second part large enough to settle the fines and condition the mud. A good rule of thumb on a dug pit is: Check the flow time across your pit. Throw a cigarette butt in the mud coming from the hole. If it makes it to the suction in less than 2 minutes, the pit ain’t big enough! There’s no way the cuttings can properly settle out with the mud going 90 miles an hour!
The advantage of dug pits is they’re simple. If you have a minimum wage crew, they can dig a pit big enough to run a Jet Ski on for practically nothing. Pit maintenance is simple, too — hey, it’s made of dirt!
To most of us, the downside to dug pits is the digging. You are going to need a backhoe. Wonderful device. The only problem for most drillers is that after pit-digging, it just sits there costing you money until it’s time to re-landscape the customer’s yard. On new construction locations that will be landscaped later, a dug pit usually is no problem. But in an existing yard with thousands of dollars worth of beautiful landscaping, digging a strip mine is not a good way to endear yourself to the customer. Add to this the possibilities of cutting gas or electric lines or other utilities, and the downside of dug pits starts to become apparent.
Now that I’ve covered a little bit of the benefits of good solids control as well as the historical methods, next month I’ll go into the newer, more efficient and, even more important, more profitable methods of solids control. Until then, keep turning to the right!