Drilling Techniques
Water well drilling techniques vary dramatically geographically throughout the country, and even widely from company to company in given areas. There are four primary methods of water well drilling technology.
Well Digging or Boring
The oldest form of well construction, hand digging of course dates to prehistoric times. Jacob's well in the Bible was dug by hand and exist to this day as a water supply. In the last 125 years or so, various machines have been manufactured that dig or bore the hole by scooping bits of earth at a bite and dumping them above ground. These wells are usually limited to depths of less than 100' deep and are typically quite large in diameter with typical diameters being 16" to 42". This method of well construction has been decreasing consistently over the last 40 years due to the number of problems and limitations associated with the method. Problems with this method of well construction are: The depth limitations of this method usually results in a well completed in formations that are less than the best quantity and quality water available. The large diameter cement casings usually used are difficult or impossible to properly seal from surface contamination. The large sizes involved make it economically unfeasible to use well screens often resulting in sandy water problems with occasional or persistent cloudy water. Also, the shallow aquifers these wells produce from are usually subject to surface contamination such as man-made chemicals and waste.
Percussion Drilling
Percussion drilling is the second oldest method of drilling known. In percussion drilling, commonly called cable tool drilling, a long heavy bit or tool suspended by a cable is lifted and dropped repeatedly to "pound" the hole in the ground. As the bit pounds the hole deeper, steel casing is driven down the hole to within a few feet of the bottom of the hole. This method of drilling began hundreds of years ago, and has been used for both water well drilling and oil well drilling. While percussion drilling is painfully slow, the method can be used in any type of geology dependably. This method of drilling is mostly obsolete in the United States.
Air Rotary Drilling
Air rotary drilling is the newest drilling technology available, and is vastly superior in certain geologic conditions to any other method. Air drilling is done by rotating hollow drill pipe with a bit on the bottom while blowing very high volumes of air through the drill pipe and out the bit at such force that the air will blow the drilled materials (cuttings) up and out of the hole. Air drilling can only be used in formations that are relatively stable and consolidated. In the Northeast Texas area this method cannot be used due to the very unconsolidated and unstable nature of the formations we must drill in.
Mud Rotary Drilling
Mud rotary drilling was developed over the last decade of the 19th and the first half of the 20th century and remains the primary method of well drilling for oil and water in areas where unconsolidated formations exist. This is the method of drilling used across Northeast Texas. While mud rotary drilling is somewhat slower than air rotary drilling, the presence of the drilling mud in the hole provides support to the hole and maintains hole stability long enough to finish the well construction. Without the presence of the mud column, air rotary drilling suffers from hole collapse problems in areas with unconsolidated formations. In our area these collapse problems would be so severe as to cause total loss of the hole. In mud rotary drilling, a bit is attached to a hollow drive pipe (known as the kelly) which is driven (rotated) by a rotary table. "Mud" (a mixture of water and drilling additives) is pumped through the rotating kelly and out the bit. As the bit cuts hole, the mud circulating out the bit carries the cut materials (known as cuttings) up the hole, out a trench and into the settling pit where the cuttings will settle. The mud then flows by another trench from the settling pit to the suction pit where it is pulled up from the pit by a suction hose into the mud pump and is re-pumped back through the kelly and bit and so on. When the kelly has drilled all the way down, it is pulled up, disconnected from the bit, and set aside. A joint of drill pipe is then connected to the bit and the bit is lowered back down the hole until the top of the joint of drill pipe is resting on the rotary table. The kelly is then connected to the drill pipe, lowered back into the rotary table and the drilling process begins again as before. As each joint is drilled down, more pipe is added in the same manner until the hole is completed to the final depth. Various additives are used in the drilling fluid to lubricate the bit, seal the wall of the hole and provide support to the wall of the hole.
Well Contruction Techniques
All wells in Northeast Texas draw there water from layers or "beds" of sand which are saturated with water. These beds of sand when saturated with water are called aquifers. Well construction is engineered to draw water from a bed of water sand while keeping the sand from entering the well with the water. There is much more to quality well construction than meets the eye, and unfortunately, few customers know enough about well construction to know how to determine which contractor they should use. Driller experience, reputation and references can help in the decision making process.
While all well drillers in Northeast Texas use very similar drilling methods, attention to detail separates the best from the rest. The first difference is found in the discipline employed by the driller to plumbness of the hole, selection of tooling and discipline employed in following a rigorous program in making and preserving the hole. The second difference in well quality comes from the experience of the driller in assessing the samples of cuttings as they rise from the hole during the drilling process and by "reading" the way the drilling takes place as the bit penetrates the formations. The third difference comes in the way a driller completes the well. There are as many different well completion techniques as there are well drillers. C. Miller Drilling uses two types of well completion depending on the drilling circumstances of the particular job. These techniques are varied as needed to fit the conditions and requirements of various projects.
One Piece Wells
This method of well construction is used in areas where geologic conditions are stable enough to ensure that the well can be completed before the formations begin to collapse. When constructing a one piece well, we start by drilling a consistent single diameter hole from the ground down to the bottom of the well. Once the hole is completed and the decisions have been made concerning where and how much well screen will be installed in the well, we prepare the materials for installation. We then "ream", or wipe the hole, a procedure where we re-run the bit down the hole with rotation and mud circulation, in a joint by joint manner, usually with multiple passes per joint. This procedure is to ensure a very clean borehole. Once the bit is back to bottom, we then "thin" the hole by pumping fresh, clean water down the drill pipe, out the bit and up through the hole to replace the thick and heavy solids-laden drill fluid with the thin water. The drill pipe are then removed from the hole and the casing and screen installed. A small "tremie" pipe is attached to the casing above the screen that extends to the ground for cement injection after the gravel is in place. The screen is placed adjacent to the desired water producing sand formation. Stainless steel centralizers are placed every 10' throughout the screened area to assure equal gravel placement around the screen throughout the screened zone. Gravel is then slowly poured down the hole around the casing. As the gravel descends down the hole it pushes water down the hole along with it. The descending water "U-tubes" down and through the well screen and back up the casing and is re-directed down the hole as more gravel is poured. This "U-tube" flow of water is carefully throttled to help carry the gravel down the hole as if it were being pumped. When the gravel has risen above the top of the screen, the U-tube flow suddenly stops, indicating to the driller that the proper amount of gravel is in place. Cement is then pumped down the tremie pipe just above the top of the gravel to prevent any co-mingling of water from strata above the screen. Next, the well is purged by air jetting (see "Purging The Well" below). Finally, the well is dis-infected and the required surface cementing is done. The advantage of this method of well drilling is that large diameter screen is installed in the well providing for highly efficient water production, and allowing for possible installation of a secondary screen should it ever be needed.
Two Piece Wells
This method of well construction is used where well depths are unusually deep and/or where geologic conditions threaten probable hole problems such as sand collapse or swelling or crumbling shales. In this method, we drill a large diameter hole down to the top of the water bearing formation, and a smaller hole is drilled through the water formation to the bottom. Once the holes have been drilled the upper hole is reamed as mentioned in the one-piece drilling method above, but the drilling mud is not thinned. Leaving the heavier mud in the hole provides greater support to very unconsolidated and/or troublesome formations. Then we install the casing in the larger diameter hole and a short distance down into the smaller diameter hole. A rubber "shale trap" packer attached around the casing seats into the top of the smaller hole thus sealing the deeper, smaller hole off from the larger hole above it. At this point, we cement the casing above the packer by way of tremie pipe just as in the one-piece well construction. Next, after the cement has cured, a small eccentric bit is lowered through the casing into the smaller hole is used to "ream" or wipe the hole through the producing zone. The drilling fluid is then thinned and the drill pipe is removed from the hole. Well screen, with centralizers every 10', is then lowered through the casing on plastic coil pipe into place into the water formation. The screen is installed from the bottom of the formation up to a point 20' to 60' up into the well casing. The gravel is then poured down the casing and a small cable with a steel rod at the end is used to "feel" and measure the gravel level. When gravel has filled the lower hole and extended up into the well casing a distance of 20' to 50', we unscrew the plastic coil pipe off the screen and remove it from the well. The well is now ready for purging by air jetting (see "Purging The Well" below). Finally surface cementing is done and the pump system installed. The advantage of this method of construction is that the upper hole can be cased while the drilling fluid is heavy with additives ensuring better hole stability and once the casing is in place, the lower hole can be reamed and thinned without concern of encountering any problems from all the hole above the water formation. This allows the driller to fight one battle at a time whenever mother nature is being unusually obstinate.
Purging the Well
Purging or "jetting" a new well is done by running an air pipe down the well to the depth that we anticipate the pump to be installed or deeper and "pumping" the well with air. When we inject high volume air in the well, it blows the water out of the well. More water then enters the well and is also blown out and so on. This purging removes the mud from the gravel pack and prepares the well for the pump installation. More than simply pumping the well with the air, we stop and start the air to "surge" the well a number of times during this process. The surging of the air momentarily reverses the flow of water back through the well screen and into the wall of the formation, breaking loose more mud and solids from the gravel pack wall and removes them from the well. As the jetting continues, the well will produce more and cleaner water. Purging the well with air also allows us to gauge the well production at different depths so that we can determine exactly what depth the pump should be hung at and how much we can expect from that particular well with a certain size pump. This process is essential to installing a good well.
Installing the Pump Station
Just as there are as many well construction techniques as there are well drillers, so are there as many different ways of engineering and installing pump systems in the well. Techniques must be altered to match the different requirements of projects. On deep wells that are for domestic use, C. Miller Drilling installs hydrodynamic pressure tanks along with automatic air volume controls. These are installed instead of bladder type pressure tanks because they provide for a natural removal of Hydrogen Sulfide (sulfur or rotten egg smell) from the water. Four custom made proprietary controls work together to make a trouble free automatic air volume control system. While Hydrogen Sulfide is usually found in small amounts, the use of the hydrodynamic pressure system as opposed to use of a bladder tank can be the difference between a satisfied well customer or a dissatisfied customer. C. Miller Drilling takes pride in their experience and expertise in installing truly trouble free air volume control systems. Customers often may not know exactly how much water they need. Our staff takes great effort to help determine what your true water needs are. Too small of a pump system will leave you unhappy, and too large will mean an unnecessary waste of money in the initial installation and in future service cost.
