water well drilling mud pump free sample

There are many different ways to drill a domestic water well. One is what we call the “mud rotary” method. Whether or not this is the desired and/or best method for drilling your well is something more fully explained in this brief summary.

One advantage of drilling with compressed air is that it can tell you when you have encountered groundwater and gives you an indication how much water the borehole is producing. When drilling with water using the mud rotary method, the driller must rely on his interpretation of the borehole cuttings and any changes he can observe in the recirculating fluid. Mud rotary drillers can also use borehole geophysical tools to interpret which zones might be productive enough for your water well.

The mud rotary well drilling method is considered a closed-loop system. That is, the mud is cleaned of its cuttings and then is recirculated back down the borehole. Referring to this drilling method as “mud” is a misnomer, but it is one that has stuck with the industry for many years and most people understand what the term actually means.

The water is carefully mixed with a product that should not be called mud because it is a highly refined and formulated clay product—bentonite. It is added, mixed, and carefully monitored throughout the well drilling process.

The purpose of using a bentonite additive to the water is to form a thin film on the walls of the borehole to seal it and prevent water losses while drilling. This film also helps support the borehole wall from sluffing or caving in because of the hydraulic pressure of the bentonite mixture pressing against it. The objective of the fluid mixture is to carry cuttings from the bottom of the borehole up to the surface, where they drop out or are filtered out of the fluid, so it can be pumped back down the borehole again.

When using the mud rotary method, the driller must have a sump, a tank, or a small pond to hold a few thousand gallons of recirculating fluid. If they can’t dig sumps or small ponds, they must have a mud processing piece of equipment that mechanically screens and removes the sands and gravels from the mixture. This device is called a “shale shaker.”

The driller does not want to pump fine sand through the pump and back down the borehole. To avoid that, the shale shaker uses vibrating screens of various sizes and desanding cones to drop the sand out of the fluid as it flows through the shaker—so that the fluid can be used again.

When the borehole has reached the desired depth and there is evidence that the formation it has penetrated will yield enough water, then it’s time to make the borehole into a well.

Before the well casing and screens are lowered into the borehole, the recirculating fluid is slowly thinned out by adding fresh water as the fluid no longer needs to support sand and gravel. The driller will typically circulate the drilling from the bottom up the borehole while adding clear water to thin down the viscosity or thickness of the fluid. Once the fluid is sufficiently thinned, the casing and screens are installed and the annular space is gravel packed.

Gravel pack installed between the borehole walls and the outside of the well casing acts like a filter to keep sand out and maintain the borehole walls over time. During gravel packing of the well, the thin layer of bentonite clay that kept the borehole wall from leaking drilling fluid water out of the recirculating system now keeps the formation water from entering the well.

This is where well development is performed to remove the thin bentonite layer or “wall cake” that was left behind. Various methods are used to remove the wall cake and develop the well to its maximum productivity.

Some drillers use compressed air to blow off the well, starting at the first screened interval and slowly working their way to the bottom—blowing off all the water standing above the drill pipe and allowing it to recover, and repeating this until the water blown from the well is free of sand and relatively clean. If after repeated cycles of airlift pumping and recovery the driller cannot find any sand in the water, it is time to install a well development pump.

Additional development of the well can be done with a development pump that may be of a higher capacity than what the final installation pump will be. Just as with cycles of airlift pumping of the well, the development pump will be cycled at different flow rates until the maximum capacity of the well can be determined. If the development pump can be operated briefly at a flow rate 50% greater than the permanent pump, the well should not pump sand.

Mud rotary well drillers for decades have found ways to make this particular system work to drill and construct domestic water wells. In some areas, it’s the ideal method to use because of the geologic formations there, while other areas of the country favor air rotary methods.

Some drilling rigs are equipped to drill using either method, so the contractor must make the decision as to which method works best in your area, for your well, and at your point in time.

To learn more about the difference between mud rotary drilling and air rotary drilling, click the video below. The video is part of our “NGWA: Industry Connected” YouTube series:

Gary Hix is a Registered Professional Geologist in Arizona, specializing in hydrogeology. He was the 2019 William A. McEllhiney Distinguished Lecturer for The Groundwater Foundation. He is a former licensed water well drilling contractor and remains actively involved in the National Ground Water Association and Arizona Water Well Association.

To learn more about Gary’s work, go to In2Wells.com. His eBooks, “Domestic Water Wells in Arizona: A Guide for Realtors and Mortgage Lenders” and “Shared Water Wells in Arizona,” are available on Amazon.

The 2,200-hp mud pump for offshore applications is a single-acting reciprocating triplex mud pump designed for high fluid flow rates, even at low operating speeds, and with a long stroke design. These features reduce the number of load reversals in critical components and increase the life of fluid end parts.

The pump’s critical components are strategically placed to make maintenance and inspection far easier and safer. The two-piece, quick-release piston rod lets you remove the piston without disturbing the liner, minimizing downtime when you’re replacing fluid parts.

Mud pumps, or mud drilling rigs, are also used as water well drilling rigs, to address water concerns at the bottom of the mines. Mud pumps, also known as mud drilling rigs, are water well drilling rigs that are used to extract water from pits, and mud drilling rigs. The mud water drilling rig is also called as water well drilling rigs, and are also called as water well drilling rigs. The mud pumps, mud drilling rigs, are also called as water well drilling rigs, for example, droplets or mud pumps. They are designed to cut slurry from pits, mud pits, and mud drilling rigs. The most common mud pumps and mud drilling rigs are also called as water well drilling rigs, to mud pits.

A water well drilling rig can consist of a large amount of mud, which is easily drained by due to the conditions of the water being high. There is also a band of mud trucks and drilling holes that are adequate for flowing water.

A gasoline powered pump, also known as an off-road mud drilling rig, is a good choice for people that choose either a gasoline-powered pump or a water well driller rig. Gasoline-powered water well driller rig, for example, is a type of water well drilling rig that has two or more volt engines. On the other hand, a gasoline-powered water well driller rig is hard to distinguish from one of these two. Generally speaking, a gasoline-powered water well driller rig is one with the energy of a day, it is important to consider the type of water well drilling rig that is powered by a gasoline-powered pump, for instance, is a by-product of the two types of water well drilling rig. For instance, a gasoline-powered water well driller rig is by one that is high-pressure, and a two-stroke engine.

Choosing the mud pumps depends on the size, the course of time, and the surface of the water. For instance, a one-stroke mud pumps depends on the size and the type of mud pumps. For instance, gasoline-powered is an electric version of the water well drilling rig.

OK, all y’all air drillers just thumb on over to Porky’s column or something. This is for mud drillers. On second thought, I know a lot of you air guys drill about three mud wells a year, and consider it a hassle to rig up mud. So, maybe something I say will be interesting …

The mud pump is the heart of the circulating system, and mud is the blood circulating in the hole. I’ve talked about mud before and will again, but this month, let’s talk about the pump.

Historically, more wells, of every kind, have been drilled with duplex pumps than any other kind. They are simple and strong, and were designed in the days when things were meant to last. Most water well drillers use them. The drawbacks are size and weight. A pump big enough to do the job might be too big to fit on the rig, so some guys use skid-mounted pumps. They also take a fair amount of horsepower. If you were to break down the horsepower requirements of your rig, you would find out that the pump takes more power than the rotary and hoist combined. This is not a bad thing, since it does a lot of the work drilling. While duplex pumps generally make plenty of volume, one of the limiting factors is pressure. Handling the high pressures demanded by today’s oil well drilling required a pump so big and heavy as to be impractical. Some pretty smart guys came up with the triplex pump. It will pump the same — or more — volume in a smaller package, is easy to work on and will make insane pressure when needed. Some of the modern frack outfits run pumps that will pump all day long at 15,000 psi. Scary. Talk about burning some diesel.

The places that triplex pumps have in the shallow drilling market are in coring and air drilling. The volume needs are not as great. For instance, in hard rock coring, surface returns are not always even seen, and the fluid just keeps the diamonds cool. In air drilling, a small triplex is used to inject foam or other chemicals into the air line. It’s basically a glorified car wash pump. The generic name is Bean pump, but I think this just justifies a higher price. Kinda like getting the same burger at McDonald’s versus in a casino.

One of the reasons water well drillers don’t run triplex pumps, besides not needing insane pressure, is they require a positive suction head. In other words, they will not pick up out of the pit like a duplex. They require a centrifugal charging pump to feed them, and that is just another piece of equipment to haul and maintain.

This brings me to another thought: charging. I know a lot of drillers running duplex pumps that want to improve the efficiency of their pumps. Duplexes with a negative suction head generally run at about 85 percent efficiency. The easy way to improve the efficiency is to charge them, thus assuring a 100 percent efficiency. This works great, but almost every one of them, after doing all that work and rigging up a charging pump, tells me that their pump output doubled. Being the quiet, mild mannered type that I am, I don’t say “Bull,” but it is. A duplex pump is a positive displacement pump. That means that it can deliver no more than the displacement it was designed for. You can only fill the cylinder up until it is full. It won’t take any more. The one exception to this is when you are pumping at very low pressure. Then the charging pump will over run the duplex, float the valves and produce a lot more fluid. Might as well shut off the duplex and drill with the charging pump.

Another common pump used in the water well industry is the centrifugal. You see them mostly on air rigs that don’t use mud too often. They have their place, but are a different breed of cat. They are not positive displacement. Flow is a function of speed and horsepower up to the limits of the pump. After that, they just dead-head. With large diameter drill pipe they make a lot of mud, but after the hole gets deeper, friction losses — both inside and outside the drill pipe — build up. This means that the deeper you go, the less circulation you have. This slows the whole process. Positive displacement pumps don’t do this; they pump the same per stroke regardless of pressure. It just takes more horsepower. Also, displacement calculations like bottoms-up time and cement placement are just about impossible. One way to get around the limited pressure of centrifugal pumps is to run two of them in series. I’ve seen a few of these rig-ups and they work very well for large diameter drilling. They will make almost the same pressure as a big duplex for a lot less money. They are still variable displacement, but they roll so much fluid that it doesn’t seem to matter. And run at pretty reasonable depths, too: 300 to 400 psi at 400 gpm is not uncommon with two 3 x 4 centrifugal pumps in series.

I reckon there are pumps for every type of drilling. It is just a matter of using the right one correctly. I once drilled a 42-inch hole 842 feet deep with a 5½ x 8 duplex. Talk about long bottoms-up time … but we got the casing in with less than two feet of fill on bottom! Took time, but we got-er-done.

When choosing a size and type of mud pump for your drilling project, there are several factors to consider. These would include not only cost and size of pump that best fits your drilling rig, but also the diameter, depth and hole conditions you are drilling through. I know that this sounds like a lot to consider, but if you are set up the right way before the job starts, you will thank me later.

Recommended practice is to maintain a minimum of 100 to 150 feet per minute of uphole velocity for drill cuttings. Larger diameter wells for irrigation, agriculture or municipalities may violate this rule, because it may not be economically feasible to pump this much mud for the job. Uphole velocity is determined by the flow rate of the mud system, diameter of the borehole and the diameter of the drill pipe. There are many tools, including handbooks, rule of thumb, slide rule calculators and now apps on your handheld device, to calculate velocity. It is always good to remember the time it takes to get the cuttings off the bottom of the well. If you are drilling at 200 feet, then a 100-foot-per-minute velocity means that it would take two minutes to get the cuttings out of the hole. This is always a good reminder of what you are drilling through and how long ago it was that you drilled it. Ground conditions and rock formations are ever changing as you go deeper. Wouldn’t it be nice if they all remained the same?

Centrifugal-style mud pumps are very popular in our industry due to their size and weight, as well as flow rate capacity for an affordable price. There are many models and brands out there, and most of them are very good value. How does a centrifugal mud pump work? The rotation of the impeller accelerates the fluid into the volute or diffuser chamber. The added energy from the acceleration increases the velocity and pressure of the fluid. These pumps are known to be very inefficient. This means that it takes more energy to increase the flow and pressure of the fluid when compared to a piston-style pump. However, you have a significant advantage in flow rates from a centrifugal pump versus a piston pump. If you are drilling deeper wells with heavier cuttings, you will be forced at some point to use a piston-style mud pump. They have much higher efficiencies in transferring the input energy into flow and pressure, therefore resulting in much higher pressure capabilities.

Piston-style mud pumps utilize a piston or plunger that travels back and forth in a chamber known as a cylinder. These pumps are also called “positive displacement” pumps because they literally push the fluid forward. This fluid builds up pressure and forces a spring-loaded valve to open and allow the fluid to escape into the discharge piping of the pump and then down the borehole. Since the expansion process is much smaller (almost insignificant) compared to a centrifugal pump, there is much lower energy loss. Plunger-style pumps can develop upwards of 15,000 psi for well treatments and hydraulic fracturing. Centrifugal pumps, in comparison, usually operate below 300 psi. If you are comparing most drilling pumps, centrifugal pumps operate from 60 to 125 psi and piston pumps operate around 150 to 300 psi. There are many exceptions and special applications for drilling, but these numbers should cover 80 percent of all equipment operating out there.

The restriction of putting a piston-style mud pump onto drilling rigs has always been the physical size and weight to provide adequate flow and pressure to your drilling fluid. Because of this, the industry needed a new solution to this age-old issue.

Enter Cory Miller of Centerline Manufacturing, who I recently recommended for recognition by the National Ground Water Association (NGWA) for significant contributions to the industry.

As the senior design engineer for Ingersoll-Rand’s Deephole Drilling Business Unit, I had the distinct pleasure of working with him and incorporating his Centerline Mud Pump into our drilling rig platforms.

In the late ’90s — and perhaps even earlier —  Ingersoll-Rand had tried several times to develop a hydraulic-driven mud pump that would last an acceptable life- and duty-cycle for a well drilling contractor. With all of our resources and design wisdom, we were unable to solve this problem. Not only did Miller provide a solution, thus saving the size and weight of a typical gear-driven mud pump, he also provided a new offering — a mono-cylinder mud pump. This double-acting piston pump provided as much mud flow and pressure as a standard 5 X 6 duplex pump with incredible size and weight savings.

The true innovation was providing the well driller a solution for their mud pump requirements that was the right size and weight to integrate into both existing and new drilling rigs. Regardless of drill rig manufacturer and hydraulic system design, Centerline has provided a mud pump integration on hundreds of customer’s drilling rigs. Both mono-cylinder and duplex-cylinder pumps can fit nicely on the deck, across the frame or even be configured for under-deck mounting. This would not be possible with conventional mud pump designs.

The second generation design for the Centerline Mud Pump is expected later this year, and I believe it will be a true game changer for this industry. It also will open up the application to many other industries that require a heavier-duty cycle for a piston pump application.

The LS300H takes the hydraulic drill line to new depths thanks to a powerful 13-horsepower mud pump. The water well drill features the same user-friendly design and hassle-free operation as the LS200H, but with a drilling depth of up to 300 feet. Its heavy-duty welded steel frame and re-enforced table base provide added durability while the drill’s powerful hydraulics delivers pull-back and push-down forces up to 5,000 pounds. The rig’s three-way ball valve enables quick bypass mudflow when adding pipe, and the swivel base design moves the rotary aside to access the borehole.

I’ve run into several instances of insufficient suction stabilization on rigs where a “standpipe” is installed off the suction manifold. The thought behind this design was to create a gas-over-fluid column for the reciprocating pump and eliminate cavitation.

When the standpipe is installed on the suction manifold’s deadhead side, there’s little opportunity to get fluid into all the cylinders to prevent cavitation. Also, the reciprocating pump and charge pump are not isolated.

The gas over fluid internal systems has limitations too. The standpipe loses compression due to gas being consumed by the drilling fluid. In the absence of gas, the standpipe becomes virtually defunct because gravity (14.7 psi) is the only force driving the cylinders’ fluid. Also, gas is rarely replenished or charged in the standpipe.

Another benefit of installing a suction stabilizer is eliminating the negative energies in fluids caused by the water hammer effect from valves quickly closing and opening.

The suction stabilizer’s compressible feature is designed to absorb the negative energies and promote smooth fluid flow. As a result, pump isolation is achieved between the charge pump and the reciprocating pump.

The isolation eliminates pump chatter, and because the reciprocating pump’s negative energies never reach the charge pump, the pump’s expendable life is extended.

Investing in suction stabilizers will ensure your pumps operate consistently and efficiently. They can also prevent most challenges related to pressure surges or pulsations in the most difficult piping environments.

Sigma Drilling Technologies’ Charge Free Suction Stabilizer is recommended for installation. If rigs have gas-charged cartridges installed in the suction stabilizers on the rig, another suggested upgrade is the Charge Free Conversion Kits.

We have looked at drilling fluids from two points of view in this Water Well Journal column. We began by looking at the science of drilling fluids. This included defining the functions of a drilling fluid and the properties of the fluid that indicate the ability of the fluid to perform those functions. We also introduced several classes of drilling fluid additives, and when properly mixed, provide defined and measurable properties to control the subsurface geology that the bore path will intersect.

Drilling can be looked at as system drilling fluids being just one part along with geology, equipment, and fluid flow and fluid pressure. Choosing the proper drilling fluid formulation is as easy as remembering how to use the five-finger method—treat the makeup water, create suspension, protect the borehole, protect the cuttings, and address any local issues.

One of the most widespread local issues is loss of circulation. Loss of circulation is losing whole mud to the formation, which we see as getting less volume of fluid back to the surface as compared to what was pumped down.

Second, a pressure differential must exist between the pressure exerted by the fluid in the borehole and the pressure in the formation. We intuitively know the pressure exerted by the fluid in the borehole is higher than the formation pressure if we are losing drilling fluid.

An example is when drilling through a gravel formation above the water table where the void spaces are filled with air, the hydrostatic pressure of the drilling fluid is greater than the air pressure in the formation, and fluid moves into the formation. The opposite is true if we have an artesian or flowing well; the pressure within the formation is higher than the pressure exerted by the drilling fluid, and fluid flows out of the borehole.

We seldom know exactly what the pressure from the formation is in the water well drilling business. We can calculate the hydrostatic pressure of our drilling fluid by this formula:

Hydrostatic pressure in pounds per square inch (PSI) equals mud weight (MW) in pounds per gallon times the depth (D) in feet where you want to know the pressure times a conversion factor (0.052) to connect all the units of measurement.

If this drilling fluid was present in our dry gravel example above, the only thing we know for sure is the hydrostatic pressure of 52 PSI is far greater than the formation pressure. The loss of returns in the dry gravel would be almost instantaneous. As the pressure exerted by formation fluids increases, the rate of drilling fluid losses decreases.

I have only talked so far about hydrostatic pressure, which means the drilling fluid is sitting still in the borehole and not being pumped. For the drilling fluid to circulate, additional pressure needs to be added by means of a mud pump.

As mentioned in a previous column, the pressure added is used up moving the drilling fluid from the pump to the drill pipe, down the drill pipe to the drill bit, through the bit, and up the annular space to the surface.

In the annular space, the remaining pump pressure must be added to the hydrostatic pressure to get a true fluid pressure against the formation. Most of these calculations are beyond the scope of this column, but suffice it to say a circulating fluid’s pressure against a formation is greater than the hydrostatic pressure at any given point. You may have experienced this phenomenon if you have had a borehole stand full when not circulating but start losing fluid while circulating.

One takeaway from the mathematics involved is the circulating pressure can be used to calculate an equivalent mud weight if the fluid was static. This is the drilling fluid’s equivalent circulating density.

Up to this point we have put the blame for lost returns on the geology of the formations we are drilling—if it were only that simple. Sometimes we must take the blame for operator-induced errors that lead to loss of returns.

Drilling fluid properties and drilling practices can contribute to loss of circulation. The pressure formulas use mud weight in the calculations. Water weighs 8.34 pounds per gallon (ppg), so this would be the minimum mud weight used to calculate pressures. As we add solids to water—either as beneficial drilling fluid additives to create our desired drilling fluid properties or non-beneficial solids such as drill cuttings— the mud weight increases.

As mud weight increases above 8.34 ppg, the hydrostatic pressure increases and the equivalent circulating density increases. High viscosity or thicker drilling fluids require more pump pressure to initiate circulation and maintain flow and therefore increase equivalent circulating density as well. This also holds true for drilling fluids with high gel strengths.

Maintaining good drilling fluid properties and controlling the buildup of drilled solids in the fluid by effective solids control methods, all within our control, minimizes the chances of loss of returns.

This would be a good time to introduce fracture gradient. Fracture gradient is the pressure gradient at which the formation breaks. If the pressure applied by the drilling fluid is higher than the formation’s fracture gradient, the formation will break and create a potential loss of returns.

How we break circulation and pull and run pipe can lead to fluid losses. If we put the mud pump immediately full on when we are ready to circulate, we send a pressure surge through the circulating system. This can have either of two effects: We could possibly exceed the formation’s fracture gradient and fracture the formation, or the pressure could be higher than the formation fluid pressure, resulting in loss of returns.

To minimize pressure surges, bring the pump on slowly until it is at your desired flow rate. Running drill pipe into the hole can have the same effect. Since the drill bit is only slightly smaller than the hole diameter, it acts as a piston in a cylinder, pressurizing the fluid in front of it. If the surge pressure is higher than the formation fracture gradient or the formation fluid pressure, we could induce loss of returns. To control this, do not let the drill pipe free-fall into the hole but run in at a rate that allows the drilling fluid to flow around the bit, minimizing the pressure surge.

There are two directions we can go. Since loss of returns is directly pressure-related, we could find a way to lower the fluid pressure exerted against the formation by the drilling fluid. This might mean changing from conventional circulation to reverse circulation, and may not be practical.

Or it could be changing from a liquid circulating fluid to drilling with air or foam. Again, maybe not practical, and I’ll leave the air and foam drilling discussion for another day.

The only other direction to follow is adding a loss of circulation material (LCM) to our drilling fluid to plug up the loss zones and keep the drilling fluid in the borehole.

A big misconception is the plugging material needs to make a rigid plug, setting up like concrete. The plug only needs to be strong enough to redirect the direction of fluid flow. In other words, it would take more pressure to push the drilling fluid through the plug and into the formation than to flow up the annulus.

Now would you really want some of these things in a water well? No, not really, because they are organic materials that biodegrade and can pollute the groundwater. We are more enlightened today and search out inert and nonhazardous materials that will not be harmful to the environment or human health.

Two types of acceptable LCM in water wells are spun mineral fiber products and water-swellable polymers. See your supplier of choice for specific products and trade names.

The choice of LCM depends on the severity of the loss. To cure a seepage loss, increasing the concentration of bentonite in the drilling fluid may be sufficient. The increased concentration of bentonite platelets can build a better mat to plug small openings. To plug a large void, chipped bentonite and gravel may need to be poured into the wellbore.

Any loss between these extremes will require varying concentrations of materials and material sizes and shapes. It is best to consult your drilling fluids supplier or local mud engineer for advice on products and concentrations.

Here are some final thoughts on lost circulation. Prevent it if possible by maintaining a good drilling fluid with low mud weight. Do not let your drilled solids concentration build up in the fluid system by utilizing effective solids control.

Follow good drilling practices and pay attention to surge pressures created by the mud pump or when running pipe. Use adequate LCM concentrations during early stages of treating the loss; the problem usually gets worse with time. When possible, combine different sizes and shapes of materials to achieve a matting effect to form a plug.

Finally, I think of combating lost returns this way: I don’t know where that lost drilling fluid is going, so hit it hard and stop it because it might end up in the neighbor’s water well or basement!

5-1. Mud Rotary Drilling. Rotary drilling with mud is the most widely used method for water-well construction. A rotary drill rig has three functions: rotating the drill string, hoisting the drill string, and circulating the drilling fluid. A bit is rotated against the formation while mud is pumped down the drill pipe, through ports in the bit, and back to the ground surface through the annulus between the drill pipe and the borehole wall. (Table 5-1 shows the relative performance of drilling methods in various geologic formations.) Drill cuttings rise to the ground surface in the drilling fluid. Rotary drilling is sometimes called mud rotary drilling. Drill pipes or rods are joined to a bit to form the drill string. The drill pipe is the link transmitting torque from the rig to the bit, and the pipe carries the drilling fluid down the hole.

a. Rotary Rigs. Rotary rigs vary in design. Drilling rigs are truck- or trailer-mounted and are powered by an on-board engine or by a PTO from the truck transmission. Power is delivered to the various components through hydraulic pumps and motors or through mechanical transmissions and clutches and geared on roller-chain drives. Many drill rigs may use both mechanical and hydraulic drives. Torque is applied to the drill string, which rotates by using three basic designs--rotary table, top head, and quill-and-drive bar. Military drilling machines use rotary table drives.(1) Rotary Table. The rotary table is a rotating platform that transmits torque to the drill rod through the kelly. The kelly, which is attached to the mud swivel, is the uppermost section of the drill string that passes through the rotary table. The drill string may be square, hexagonal, or round with grooves or flukes on the outside wall. The drive kelly bar slides through the rotary table while rotating. By removing the kelly bar, you can add drill pipe and work the pipe through the open hole in the rotary table. The rotary table normally is a mechanical, positive drive mechanism.

(4) Mud Pump. A mud pump (Figure 5-1) on a rotary drill is usually a positive-displacement, double-acting piston pump with capacities ranging from one to several hundred GPM at pressures up to several hundred psi. Power may be provided through a mechanical PTO and clutch, with or without a separate transmission. Power may also be provided by a separate engine or a hydraulic or air motor. Other types of pumps are often used successfully, but their limited pressure capacity may jeopardize the success of the drilling operation. Most well-drilling machines have dual piston, double-acting, positive-displacement mud pumps. Pump capacity (volume and pressure) can limit the effective depth of a drilling operation. The horsepower required to drive a mud pump often exceeds the power required to hoist and rotate the drill string.

c. Rotary Operation. Standard rotary drilling involves the bit rotating against the formation. Drilling fluid is pumped through the drill string and face of the drill bit and backup the annulus to the surface. The rotary action of the bit loosens the material, while the drilling fluid cools and lubricates the drill pipe and bit and carries cuttings to the surface. The drilling fluid is under high hydrostatic pressure and supports the wall of the borehole against caving. The properties of the drilling fluid are important to the drilling operation. Well drillers must have knowledge of drilling fluids and their use for successful rotary drilling. Drillers must also know about drilling-fluid additives used to prevent problems in drilling. Preventing drilling problems, such as an unstable borehole wall or a stuck tool, is easier than fixing the problem after it occurs. See paragraph 5-1e for information on drilling fluids.

Before drilling with mud, build a mud pit. The pit may be either a portable pit or an excavated mud pit. The decision depends on the hole depth and the alternatives available. See paragraph 5-1e(9) for more information on mud pits.

d. Variables. Bit design, weight on bit, rotation speed, fluid consistency, and cumulation pressure and velocity affect rotary drilling. Experience helps the driller handle unique problems and conditions. Continue to experiment wherever you drill to develop the best drilling procedure. Before starting the hole, plumb the kelly to provide a straight hole (Figure 5-3).

(2) Weight on Bit. Adding weight on the bit increases the torque required for rotation. Too much weight can cause excessive penetration and produce cuttings that are too large and heavy. Large cuttings are difficult to wash out and may cause gumming and premature failure of the bit. Insufficient weight reduces or stops penetration and can produce fine cuttings. In cohesive soils, fine cuttings may thicken the drilling fluid and fail to settle in the mud pit. How weight is applied can also cause serious alignment problems and difficulty in well construction. Rotary-drilled boreholes spiral slightly and are seldom straight. Once spindling occurs, weight added by pulling down with the drill rig bends the string and magnifies the deviation. You should never use the chain pulldown to advance the hole beyond the first run (20 feet). Ideally, keep the drill string in tension. Add drill collars (heavy wall drill steel) at the bottom just above the bit. See Table 5-3 for drill collar weights.

Bit weight required to cut rock depends on the design of the bit and the strength of the rock. Roller bits need a minimum of 2,000 psi of bit diameter for soft rock and shale and a maximum of 6,000 psi of bit diameter for hard rock. Before drilling, add drill collars instead of drill pipe until the load is sufficient for reasonable cutting. As you dig deeper and add drill pipe, you may have to hold back on the drill string. See Table 5-4 for weight on bit and rotary speed.

(5) Fluid Requirements. Fluid requirements depend on size, weight, nature of cuttings, and circulation velocity. Velocity depends on capacity and condition of the mud pump, annular area in the borehole, and the stability and permeability of the formation. See paragraph 5-1e for more information on drilling fluids.

(6) Circulation Pressure and Velocity. These elements of the drilling fluid are controlled by the pump capacity and speed. The fluid"s density, velocity, and viscosity let it carry cuttings. If the drilling fluid is too thick, cuttings will not settle in the mud pit. Sufficient velocity with a fluid of low viscosity (even water) will carry drill cuttings to the surface. Excessive velocity will erode the wall of the hole to the extent of failure.

Pump pressure results from flow resistance caused by viscosity, friction, weight of the fluid column, or restrictions in the circulating system. Pressure should be exerted at the ports in the bit, causing a downward jetting as the fluid exits. Regulate mud-pump pressure by varying the RPM of the pump. Mud-pump pressure against the bit is not harmful if it does not exceed the operating pressure of the pump. Other sources of fluid pressure can be detrimental. Pressure from friction occurs if the drill string is long for its inside diameter or pipes are internally upset. Frictional pressure increases wear in the pump. Pressure from the weight of the fluid column in the annulus or from a restriction in the annulus caused by an accumulation of cuttings indicates insufficient cleaning. This type of pressure can cause formation damage, resulting in lost circulation and wall damage.

e. Drilling Fluids. Drilling fluid is circulated in rotary drilling to cool, clean, and lubricate the drill string, to flush cuttings from the hole, and to stabilize the borehole wall. Water is the basic fluid and is satisfactory for lubricating and cooling the tools. However, water has limited abilities to carry cuttings and stabilize the borehole wall. Many drilling fluid additives are prepared and formulated for various purposes. Polymer fluids and water-based clay fluids (muds) are the primary additives used in water-well drilling. Table 5-5 lists drilling fluids.

Mud cools and lubricates through heat absorption from the bit and reduction of drill-string abrasion against the borehole wall. Heat is generated as the bit scrapes and grinds. Without the cooling fluid, the bit would overheat and be useless. Research indicates that removing the cuttings around and under the bit is the most important factor in keeping the bit cool. Requirements for cooling fluid are less than those for removing the cuttings.

Therefore, if you keep the borehole clean with the fluid as you drill, you also cool and lubricate. This is true with clay muds and polymer fluids. Clay muds are colloidal suspensions. Solutions are chemical mixtures that cannot be separated by simple filtering. Suspensions are physical mixtures of solids and liquid that can be separated by filtering. This distinction underlies the difference in behavior between drilling polymers (solutions) and drilling muds (suspensions). You can mix natural clays with water for use as a drilling mud. Drillers often use water in shallow clayey strata and depend on the formation clay to produce a suitable mud. Natural-clay mud properties are marginal for good water-well drilling.

Hydrostatic pressure allows the fluid to support the borehole wall and is a function of the density or weight of the mud column. Important characteristics of a drilling mud are viscosity and weight to carry cuttings, gel strength, yield point, and active clay solids for filter cake. Use the following formula to calculate hydrostatic pressure:

(1) Polymers. Polymer fluids are water-based and very low in solids. The polymer admixture can be organic, inorganic, natural, synthetic or synthetically formulated natural polymers. Polymer additives are formulated for various drilling-fluid purposes and can be used alone or to enhance clay muds. Polymers, containing salt and other contaminants, are available and are compatible with water. Polymers are more sensitive to pH than are bentonite muds. Change the pH to effect desirable changes in the polymer fluid. Drilling-fluid weight impacts drilling rate and high-density drilling fluid reduces drilling rote. There is strong indication that the solids of a fluid have a similar effect as density. Polymer fluids are very different from clay muds because a large part of the polymer is soluble in water and becomes a solution when mixed with water. Long, complicated molecular chains tie up the water and can build viscosity without solids. In water-well drilling, many polymers are manufactured for producing drilling fluids, such as E-Z Mud, Revert, and Poly-Sal. E-Z Mud is a synthetic, inorganic polymer. Revert is a natural, organic polymer fluid derived from the guar plant.

Polymers are generally best mixed through a mud gun. Polymers used for special purposes are available from the manufacture complete with specifics on how to use the product. Most polymers can hydrate more water than a high-grade bentonite. Up to ten times more bentonite is needed to build the same viscosity in a given amount of fluid, depending on the quality of the polymer. A polymer does not fully hydrate as quickly as bentonite. Mix the polymer very slowly through the mud gun a minimum of four hours before using for more complete hydration. The fluid will thicken as hydration continues, so do not mix to the desired viscosity. Some polymers possess physical qualities that can result in unusual hydration, gelling and viscosity. Follow the manufacturer"s recommendations for hydration. Factors that affect the viscosity are quality of polymer, concentration and size of colloid, metallic ions in mixing water, temperature, rate of shear, and pH.

Water is the primary building block for drilling fluids. Water quality affects the overall performance of drilling fluids. The action of bentonite in water is seriously impaired by dissolved acids or salty substances. Acidic water usually contains dissolved metals that cannot be used unless treated. Hard water affects the suspending and sealing qualities of bentonite. You can test the pH level by using paper pH strips. The pH level should be 8 to 9. If the water is too acidic, treat it with soda ash at a ratio of 1 to 5 pounds of soda ash per 100 gallons of water. Following treatment, retest the pH level as before.

Do not use water from wetlands, swamps, or small ponds for mixing drilling fluids because the water may be contaminated. If you use water from these sources, chlorinate the water before making the drilling fluid. Be careful because chlorine removes metallic ions that are necessary for viscosity in polymers. Adjust the pH of drilling water to 7.5.

Temperature affects the viscosity and stability of some polymers. Consider the following examples:Seven pounds of Revert per 100 gallons of water at 45°F yields Marsh funnel viscosity of 125 seconds per quart. The same mix at 85°F yields 70 seconds per quart.

Polymer drilling fluids can break down viscosity. Without treatment, the viscosity of some polymers (Revert) completely breaks down in one to six days depending mainly on temperature. You can correct this by adding chlorine. Revert requires Fast Break; E-Z Mud needs sodium hypochlorite at a ratio of 2 quarts for every 100 gallons of water. Other polymers, such as E-Z Mud and Poly-Sal, maintain their viscosity for long periods of time since natural breakdown is not significant. Table 5-6 lists additives for drilling fluids.

Some drilled fines (clay, silt) circulate back down the hole. Recirculated solids are much less a problem with polymer fluids than with clay fluids. Revert will not hydrate in water containing any appreciable amount of borate. However, Borax can be used to produce a gel plug in hydrated guar-gum polymer. With a pH of 7.5, the borate cross-links the polymeric chains and forms a strong three-dimensional molecular gel. If a strong gel plug is necessary to get through a lost circulation zone, mix 1 cup of borax in 5 gallons of water and pour slowly into the pump section while pumping at idle speed. When the berated fluid (stringy gelled mass) recirculates, stop pumping for one-half hour. Resuming normal drilling should be possible after wasting the borated fluid. Repeat the procedure, if necessary. Although the polymer fluid is not thixotropic and has no gel strength, it thins somewhat while being pumped.

Polymer fluids build a type of membrane on the wall different from clay mud. Unnatural clay particles (bentonite) are not introduced into the hole. Since the polymer fluid is partly a thick solution, infiltration into the permeable wall is reduced. However, insoluble portions of some polymer colloids do exist. The insoluble and cuttings are surrounded with thick coatings that are more impermeable per unit thickness than a bentonite filter cake. The insoluble and cuttings seal the wall of the hole with a thinner, less active layer. The impermeable layer performs the same function as the filter cake in clay muds but does not restrict the annulus.

The colloids in the polymer fluid are nonionic, have no chemical interaction, and are easier to remove in water-well development. When the viscosity of the fluid is broken, much of the cohesive function of the thin film becomes a water-like liquid and is washed out of the water well. Field testing of polymer fluids, using the falter press and the Marsh funnel, yields different results. The mud balance for measuring fluid density does not change. Weighing of the polymer fluid is limited. You can add sodium chloride to the fluid to bring the weight up to about 10 pounds per gallon. The addition of heavy solids (ground barite) is ineffective because of the polymer fluid"s lack of thixotropic qualities.

(2) Mud Products. Commercially processed clays for drilling are bentonite and attapulgite. Bentonite is superior except in brackish or salty water. (Use attapulgite in these waters.) Bentonite forms naturally from decomposition of volcanic ash when ground. Bentonite consists of aggregates of flat platelets in face-to-face contact. Bentonite is mined in many states, but the best grade (Wyoming bentonite) is mined only in Wyoming and South Dakota. Wyoming bentonite contains sodium montmorillonite (the active part of the clay mineral) and is small in size, which is important in building viscosity.

Mud drilling fluids should be mixed with a mud gun. When agitated and sheared with water, the bentonite platelets absorb more than 25 times their own weight in water, separate, and swell. The amount of surface area wetted determines the ability of the particle to build viscosity. One ounce of Wyoming bentonite dispersed in water has more surface area than five football fields. Interparticle activity between platelets gives the mud its gel properties. The chemical composition of the mixing water affects the ability of bentonite to develop desirable qualities. These qualities can be manipulated by adding small amounts of various chemicals.

(3) Mud Viscosity. True viscosity is a term relating only to true (Newtonian) fluids, such as water, and is a proportional constant between shear stress and shear rate in laminar flow. Drilling muds act differently in that the proportion between shear stress and shear rate is reduced when shear rate is increased. Drilling muds are thixotropic. The viscosity of a drilling mud refers to the thickness of the mud while flowing. Gel strength is the term used to describe the thickness of drilling mud at rest. Gel strength develops over a short period of time.

Yield point is the mud quality broadly included in viscosity. You need more stress (pump pressure) to cause the gelled drilling mud to start flowing than to sustain flow once the gel is broken. The stress required to initiate shear or flow is the gel strength of the mud. The stress required to maintain shear is the viscosity. You want a higher yield strength with respect to the gel strength so the mud becomes very thin in flow shear.

The primary function of viscosity is to help lift drill cuttings from the borehole. Other mud characteristics affecting lifting capacity are density, velocity, and flow patterns. Gel strength holds the cuttings in suspension at the bottom of the hole when circulation is stopped. The stress (hydraulic pressure) required to break the gel strength to initiate cumulation can be detrimental. Required bottom-hole pressures can cause fracturing or opening of fractures in the formation, resulting in loss of drilling fluid, formation damage, and borehole wall damage. Down-hole pressure required to continue circulation depends on friction, density (or weight of fluid column), and viscosity of the mobilized fluid. These pressures can also cause serious problems. Therefore, it is desirable to use a drilling mud of relatively low density and viscosity, moderate gel strength, and high yield point relative to the gel strength (a very thin fluid in circulation).

(4) Mud Testing. The Marsh funnel (Figure 5-6) is routinely used to give an indication of thickness or apparent viscosity of drilling fluid. The Marsh funnel is 12 inches long and 6 inches in diameter and has a No. 12 mesh strainer and a 1,000-milliliter (ml) cone. The funnel has a 2-inch-long, calibrated, hard-rubber orifice with an inside diameter of 3/16 inch. The funnel"s cup is marked with a capacity of 1,000 ml. Use the following procedure for the Baroid Marsh funnel:Hold or mount the funnel in an upright position, and place a finger over the hole.

The funnel viscosity measurement obtained is influenced considerably by the gelation rate of the mud sample and its density. Because of these variations, the viscosity values obtained with the Marsh funnel cannot be correlated directly with other types of viscometers and/or rheometers. Graduated in cubic centimeters (cc) and fluid ounces, the 1,000-cc measuring cup is designed specifically for use with the Baroid Marsh funnel viscometer. A quart volume is clearly marked on the measuring cup.

You can use test readings as an indicator of changes in mud that might lead to problems. Therefore, conduct Marsh-funnel tests before beginning operations and record the findings. Take mud samples for each test from the same location in the circulating system just before returning to the hole. The apparent viscosity of the drilling mud in motion affects carrying capacity, the pump pressure (hydrostatic down-hole pressure) required for circulation, and the ability to drop cuttings in the settling pit. These characteristics are also intrinsically involved with well hydraulics, density of mud, density and size of cuttings, and particle slip.

(5) Density. The carrying capacity of a mud is affected by its density and the density of the drill cuttings. If the cuttings are denser than the fluid, they will descend. The magnitude of the difference in density, particle size, and fluid viscosity affect the rate at which a particle descends. Particle slip denotes this downward movement through the fluid. Ignoring thixotropy, the actual downward particle slip is constant regardless of velocity of flow. However, when the upward velocity of fluid exceeds the downward particle slip, the new movement of the particle is upward. Up-hole velocity plays a major role in determining the carrying capacity of the cumulating fluid. The practical limits of up-hole velocity depend on pump size and capacity, inside diameter (ID) of the drill string, jet size in the bit, viscosity of the fluid, cross-sectional area of the annulus, and stability of the borehole wall. Up-hole velocity is not as simple as the comparison of pump capacity, drill string ID, and annulus. Up-hole velocity is not a constant.

The density of the drill fluid serves other purposes in rotary drilling. Heavy fluids can control (hold down) formation pressures encountered in drilling. You can build heavy mud by adding a weighing material such as ground barite (specific gravity 4.25). Prepare drilling mud in excess of 20 pounds per gallon by using barite. First, mix bentonite and water to build viscosity. Then, add finely ground barite so the mud will hold the barite in suspension. Use heavy drilling mud only when absolutely necessary to control pressures since the muds have disadvantages. High-density mud increases pressure on the formation by the weight of the fluid column. Figure 5-7 shows the nomograph for determining the hydrostatic head produced by drilling fluids. The increased pressure is further increased by the pump pressure required to mobilize the fluid in circulation. The increased pressure can cause formation damage and loss of circulation. In formations that are strong enough to withstand the pressures without being damaged, the drilling operation can still suffer.

All cuttings should be removed from the drilling mud in the settling pits and not recirculated. Although 100 percent removal is unrealistic, well-designed mud pits and mechanical screens, desanders, and desilters materially aid in removing cuttings from the mud. Water weighs 8.34 pounds per gallon. Clean, low-solid bentonite mud can weigh 8.5 to 9.0 pounds per gallon; try to maintain that weight. Increasing density of the mud during drilling indicates that the mud contains native solids. The drill"s penetration rate could be exceeding the combined effort of the mud pit, desanders, and fluids to effectively separate solids from the drilling mud. To correct this problem, slow down the penetration rate and run the desanders to remove the solids.

You can determine the density or weight of the drilling mud using a mud balance. Fill the mudbalance cup with mud, and place the inset lid in the cup. Excess mud will be displaced through a hole in the lid. Clean the outside cup area, place the assembly on the center pivot, and balance it using sliding weight. You read mud density as pounds per gallon and pounds per cubic feet. If you know the mud weight that enters and exits the drill hole, you can evaluate the efficiency of the mud pit and mechanical separators, determine when to clean the mud pit, and tell how well the mud is cleaning the hole. If you take samples from only one location, take them from the return end of the pit.

(6) Filter Cake. Filter cake consists of solids from the drilling mud deposited on the borehole wall as the water phase is lost into the formation. Desirable properties are thinness and impermeability. Drilling mud is a colloidal suspension that can be separated by simple filtering. With the hole kept full of mud, the hydrostatic pressure inside usually exceeds the formation pressure. Occasionally, an artisan aquifer is penetrated, with formation pressure higher than the hydrostatic in-hole pressure. When the borehole pressure is higher than the formation pressure, the drilling mud tends to penetrate more permeable formations. Solids from the mud filter out and deposit on the wall, and the liquid phase of the mud (filtrate) enters the formation.

Filter cake can be compacted against the wall by the excess hydrostatic pressure in the borehole. If the drilling mud is a well-conditioned bentonite and water mixture, most of the solids plastered against the wall will be flat platelets of highly active clay. The filter cake is self-regulating based on its degree of impermeability. As long as filtrate can pass through, the filter cake continues to thicken. A thick cake detrimentally increases down-hole cumulating pressure by restricting the annulus, making it difficult to pull the drill string because of the physical size of the drill collars and bit. In deep and somewhat deviated holes, the danger of key seating increases. Because a thick filter cake is of a lower quality and depends on its thickness to be effective, it is more easily damaged and eroded. A thick filter cake may indicate that the fluid has a high percentage of native solids. You may have to clean these solids from the mud before drilling progresses.

A thin, highly impermeable filter cake bonds well to the wall and provides a surface for the hydrostatic pressures to act against to support the wall. Filtrate loss into the formation can account for significant fluid loss, if the consistency of the drilling mud is not good. Good consistency does not necessarily mean thick; it has to do with the bentonite content and the quality of falter cake. If a permeable formation is encountered with pore spaces too large to be plugged by the fine bentonite particles, the drilling mud will enter the formation. That mud loss can take the entire output of the mud pump. The drill cuttings being carried up the annulus can sometimes be beneficial. The cuttings are coarser than the bentonite particles and may help bridge across formation pores. If you use this technique, maintain the normal drilling rate to supply the cuttings. Slow down the pumping rate to reduce pressure on the formation while bridging the open spaces. With sufficient bridging, a suitable filter cake follows, circulation is regained, and normal drilling operations are resumed.

In the field, you can test the filtration properties and filter-cake thickness using the filter-press kit. This kit consists of a press with a mounted pressure gauge and a CO2 charging system that is used to simulate the hydrostatic pressure inside a 200-foot hole. By placing a sample of drilling mud in the press and charging the system, you can forma filter cake. The filter cake should be less than 2/32-inch thick.

(7) Salty Environment. A high chloride content in the mixing water causes bentonite to react anomalously or not react at all. The ground bentonite remains agitated; it does not disperse, hydrate, or swell. In salt water, bentonite is an inefficient clay additive for drilling mud. The dissolved salt is an electrolyte that changes the interparticle activity of bentonite. If you add sufficient amounts of salt water to a fresh water and bentonite mud mixture, the dispersed platelets will form lumps. Viscosity and filtrate loss increase and the mud"s ability to build a thin, impermeable filter cake decreases.

Attapulgite is often used for salty formations. The small particles produce a high surface-area-to-volume relationship and good viscosity building. Unlike bentonite, the particle shape is needle-like. Viscosity building in attapulgite depends on the entanglement of these needles. The disorderly arrangement of the particles accounts for the poor filtration qualities of attapulgite. The filter cake is more like a layer of strew or sticks. Attapulgite clay does not have the physical qualities to build a thin, impermeable filter cake. If you can mix bentonite in fresh water first and then add salt water as make-up water, the bentonite flocculates; that flocculation can be reversed by chemical treatment.

(8) Well Hydraulics. You must have a basic understanding of well hydraulics. Fluid is pumped down the drill string, out the ports in the bit, and up the annular space between the drill string and the wall. The fluid empties into the mud pit, through any mechanical solids separating equipment, and is picked up from the pit by the mud pump for recirculation. The system is intended as a conservation system. Except for mud lost into the formation or where artisan water exceeding hydrostatic pressure flows into the hole, the return is largely complete and the mud-pit level does not change. Even if the system is in equilibrium, you need to understand the up-hole rearrangement of flow patterns.

Fluids flow in two distinct patterns. Laminar flow is orderly. The streamlines remain distinct and the flow direction at every point remains unchanged with time. Turbulent flow is disorderly. The flow lines and directions are confined and heterogeneously mixed. The type of flow depends on the cross-sectional area of the fluid course and the velocity, density, and viscosity of the fluid. In water-well drilling, the cross-sectional area of the annulus is usually several times that of the inside diameter of the drill string. Because of the increase in volume in the annular space, flow at the point the fluid leaves the bit is turbulent. The fluid becomes laminar flow when it begins flowing up the annular space. The returning fluid velocity is slower and the drill fluid is more dense and probably has more apparent viscosity, which affects the flow pattern. To clean the hole and carry the drill cuttings out, turbulent flow in the annulus would be better.

For example, if you use a 3 1/2-inch ID and 4-inch outside diameter (OD) pipe to drill a 9-inch hole and pump 200 GPM, the velocity of the ID pipe is 400 feet per minute (fpm) and the velocity of the OD pipe is 75 fpm. To test cumulation at these rates (bit is 300 feet deep), pump down a marker (strew or oats). The majority of the material should take 4 minutes and 45 seconds to return (300 feet at 400 fpm takes 45 seconds and 300 feet at 75 fpm takes 4 minutes). To clean all the cuttings from a 300-foot depth with an average up-hole mud velocity of 75 fpm will require more than four minutes of pumping. Consider this concept regarding sampling cuttings from the return mud.

If cuttings remain in the annular space between the drill rod and borehole wall when circulation is stopped, they will produce a denser fluid than the clean drilling mud inside the drill rods. The denser mud in the annular space will then flow down the hole and force the clean drilling mud up the drill rods. This causes a geyser effect, and the drilling mud may shoot several feet into the air until the mud columns equalize. (Some drillers mistake this for a caving hole.) If this situation happens when adding drill rods, the circulation time should be increased after drilling down the next rod. Use the following formula to calculate the annular space volume:

(9) Mud Pits. Rotary chilling preparation is the design and excavation of an in-ground mud pit or installation of a portable mud pit and the mixing of the drilling fluid. For standard drilling operations that use well-completion kits, well depths could range from 600 to 1,500 feet. For wells up to 600 feet using the 600-foot WDS, use portable mud pits. For wells over 600 feet, use dug mud pits. In either case, you will have to clean cuttings from the pits as drilling progresses. Design considerations include the anticipated depth and diameter of the drill hole, since the material cuttings from the h