My last article focused on the case of the usage of solid control equipment in your drilling operation. For this article, I would like to explore the different options available for you to add mechanical solid control to your drilling program. I talked to four solids control system subject matter experts to supplement my opinions and experiences with that of others who may have greater experience in building, selecting, maintaining, and running solid control equipment. 

I would like to thank all four of these gentlemen for providing me with insights into their knowledge of solid control equipment and operations: Thank you, John Miller (CEO of Mud Technology International), Kenneth Martinez (Owner of Mud Puppy Corporation), Jim LaPorte (Owner of Mud Slayer Manufacturing), and Derek Anderson (President of Drilling Equipment Resources, Inc.) for your professionalism and willingness to share your knowledge.

Intelligently Selecting Your Solid Control Equipment

When selecting equipment of any type, there are details we must consider prior to purchasing said equipment. These include the average size of the boreholes you drill, the formations you work in, job site footprint, and finally, your budgetary restrictions. Luckily, solid control system manufacturers offer varied sizes and types of equipment to meet the needs of your operation. Rest assured, no matter what drilling discipline your company pursues there is likely a mechanical solid control system solution that will increase your overall efficiency, job site cleanliness, and profitability.

A common rule is that the volume of the mud tanks has a direct relationship to the amount of clean mud sent to the bit without the density of the “cleaned” mud raising to an unacceptable level and causing downhole problems. The rule of thumb is typically that your mud weight should stay below 8.8 pounds per gallon. If it reaches 9 pounds, changes must be made to avoid future problems. For a 500-foot geothermal hole six inches in diameter, there is a total volume of 735 gallons. We need 1.5 times the hole volume or a total of 1100 gallons minimum for a mechanical solids control system to work effectively. If we do not have at least 1.5 times the hole volume in our solids control tanks, we can expect for the sand content and density in our system to increase throughout the drilling process.

Not every one of the subject matter experts I talked to agrees with that calculation. Jim LaPorte of Mud Slayer Manufacturing commented, “To me, it was never about how much mud you got in your mud tank. To me, it's how good you are at cleaning the mud in the borehole.”

Jim's theory is that he likes to use the borehole as his “tank” and minimize the size of the tank on the solids control equipment he produces. I tend to agree that it is the mud sent to the hole that matters the most when utilizing any type of solids control, be that pit splash pan or mechanical. My advice is to invest in a mud testing kit that allows you to evaluate the properties of the fluid sent to the bit. Test the mud periodically through the entire drilling process.

Understanding Your Equipment

When considering buying solids control equipment, if possible, see if you can visit a customer using the solids control equipment you intend to purchase and ask their experiences with mud properties using the equipment. Remember to ask what diameters and depths the equipment has completed successfully. What type of fluid testing does the company typically do while utilizing their solids control equipment? What life expectancy of pumps and screens and other components have they experienced?

Your success depends on the formation, drilling process, and speed of your drill. Your operation may be able to use a system that is smaller than 1.5 times your maximum hole volume successfully. However, you may have to make the calculation that at some point during the drilling process you will be disposing of the mud and remixing. So, let's assume that we're going to use the rule of thumb and choose the system with at least 1.5 times the fluid capacity of the deepest hole we intend to use the system on. What do I need to know to understand the system and decide what is right for the intended operation?

Drilling Down Into the Components

Solids control equipment have two categories based on the type of motive power used to drive the system. The two motive powers are electric and hydraulic. Both types of systems used in water well and geothermal drilling will have similar components. These including a high solid handling pickup pump, a shaker system, hydro cyclone de-sanders/desilters, and the associated pumps and piping, as well as “dirty” and “clean” mud tanks.

Hydraulic systems have the advantage that they are typically smaller, more portable systems, whereas electrical systems can range from smaller, portable systems all the way to extremely large oil field-sized systems. Hydraulic systems tend to be less expensive and lighter, increasing their portability. Meanwhile, electric systems are a little heavier, even in the same size category due to the generator required to power the system. Electric systems tend to be more environmentally friendly for use in sensitive areas, as well as having the advantage of being able to run linear shakers without complicated engineering.

Let us talk about cleaning capacity and how design of the system impacts the amount of mud cleaning per minute we can expect from a given system. The first thing to talk about is the actual shaker and screens which place a G force load on the particle. The purpose of this force is to get the particle entrained inside the fluid to break through the surface tension of the mud, allowing the mud to return to the tank and the particle to fall off the end of the screen.

The screen is selected for the size of particle we intend to remove. The first-time mud that flows over a shaker is typically flowing over a screen with larger openings called scalping. This removes the largest cuttings. Fed directly from the pickup pump, the mud then falls into the “dirty” side of the tank. The dirty mud is sent to another pump and sent to the hydro cyclones. The amount of mud that the hydro cyclones can clean is a result of the size and number of the hydro cyclone cones. The diameter of the cones determines the centrifugal force the cone can put on the fluid.

The smaller diameter a cone is, the finer the particles it can remove. But the cones’ total flowrate is decreased due to its smaller size. For most water well applications, the hydro cyclone cones tend to be sub eight inches which puts them in the desalting category. The amount of mud that your system can clean is a direct result of the number of cones the system runs and the square feet of the shaker that the cones exhaust out onto.

I talked with Derek Anderson of Drilling Equipment Resources, Inc. about cone size commonly available in the equipment used in water well and geothermal drilling. Anderson commented, “Those 5 inch cones are commonly known, non-brand specific, to process up to eighty gallons a minute. However, they may only be able to give you clean sixty gallons or so fluid (per cone). Depending upon the efficiency of the system piping, the header, the system pressure, etc. If I am going to say I need so many gallons per minute of clean fluid, I need to look at those areas first.”

Linear or Orbital?

Using that logic, if our system rated at 320 gallons a minute based on four five-inch desilting cones flowing at 80 gallons a minute on to the second shaker screen, if the flow down hole is less than 225 gallons a minute, our system could run with a 100% duty cycle. But this is an oversimplification. The type of shaker (linear or orbital) and area of our screens has a direct result on our ability to clean the fluid. Orbital shakers run in elliptical motion and bounce the fluid on top of the screen. The screen is situated at a slight downward angle so the gravity will assist in the material left on the top of the screen and deposited out of the system.

Orbital shakers tend to be at a lower price point than their linear counterparts. This comes with a tradeoff as they also do not clean as efficiently. That is not to say that an orbital shaker cannot effectively clean or drill mud, however, they may struggle to remove the ultra-fines.

Linear shakers differ from orbital in that they can produce a straight motion in a 30-40° angle. This angle allows our cuttings to be conveyed uphill making for more effective cleaning and higher G forces applied to the particles entrained in the mud, allowing for smaller fines to be removed in the same screen total area.

In talking about linear shakers, John Miller of Mud Technology International commented, “You can actually raise the shaker up, allowing the liquid to pool at the back bottom of the shaker, while your solids still walk uphill and go off. This increases your efficiency and your cut point for particles, which is really what I'm looking for—to get that fine material out. If I can pull those particles out in the first circulation, then the unit will work more efficiently.” Typically, we want are fluid to pool in the back but to have only dry cuttings conveying up the last third of our desilting screen. And seizing those screens will also have a direct relationship with the formation.

What’s Next: Screen Sizing and Common Pitfalls

In the next article, we will talk about sizing the screens operating the systems and basic pitfalls encountered when first utilizing solids control equipment. Until then, keep turning to the right, be safe, and keep your mud clean.