Purpose and Importance of Proper Well Development

Well development is a process that is completed after the drilling of a borehole, installation of the casing and screen, filling the annular space with gravel pack, and grouting operations (see the Oct 6, 2020 LWS well completion blog). Well development is completed to clean the well and the surrounding aquifer of drilling mud and sediments that may impair the water flow into the well. It is the final and most important part of a well installation and completion procedure.

LWS always suggests the use of inorganic polymer mud for drilling as it is easier to clean the well. Without a proper well development, well screens may be blocked by drilling muds caked to the borehole wall and/or screens during the installation process. With any blockage related to drilling muds, the groundwater entering the well will be restricted and the well will operate at an efficiency that reduces the amount of water that can be pumped. The key purpose of the well development is to get the well to produce at its maximum rate and produce representative sand-free water from the aquifer.

Why is this important? A proper well development can improve well efficiency, lower the pumping costs, and extend pump life. Figure 1 shows the well water before, during, and after well completion.

Figure 1 - Water samples before, during, and after the well completion.

Methods for well development may include a number of techniques that can be used as standalone processes or in combination with multiple methods. These methods include a surge block, bailing, air lifting, high-pressure water jetting, and/or over-pumping to finish the development. The goal is to remove the drilling mud from the borehole and borehole wall, and to also move near-well fines from the formation matrix to allow the well to produce water at optimum efficiency. The overall objective is to make the well as efficient as possible, given the characteristics of the surrounding aquifer and the design of the well screen and gravel pack. All of these development methods are just different ways of introducing energy (in forms of moving water or air) through the well and gravel pack.

The gravel pack and well screen should be designed such that they stabilize the formation such that the passage of fines is minimized (only 5-10% of the matrix). This is so the formation matrix will be stable and the remaining formation matrix surrounding the gravel pack will not be moved through the gravel pack and screen. Which method to use depends on the purpose of the well, the aquifer characteristics, and of course, budget.

SURGE BLOCK

A surge block is a flat seal that provides a relatively tight fit inside the casing and works like a plunger. The seal is connected with a one-way valve to lift water out of the well on the up stroke and allow water through the valve on the down stroke. The block is positioned in the portion of the well where development is wanted, i.e., the screened section, and is moved to different depths in the well throughout the process.

BAILING

Bailing is like filling a bucket with well water and bring it up to the surface. The water extraction causes aquifer water to flow into the well. The bucket is a long tube with a one-way flap at the bottom, allowing water to fill when lowering the bailer down the well. When the bailer is lifted, the valve closes and the water in the bailer can be pulled to the surface. This method is often used to remove large amounts of sediment from a well.

AIR-LIFTING

Air-lifting involves introducing compressed air into the well to lift the water in the well while pumping out the water. A tube or pipe with air supply is introduced into the well. The compressed air forces water to the surface when the pressure exceeds the weight of the water column, allowing the water from the aquifer to flow into the well. The fines and sediment from the gravel pack are transported upward and removed from the well. There are two main methods of air lifting, single and dual pipe.

Single pipe air lifting is simply putting one pipe down the well and forcing compressed air into the well, causing the aerated water to rise to the surface. This method introduces significant energy to the gravel pack and is good for cleaning very dirty wells. A caution with this type of air lifting is that it should be staged so compressed air is not introduced for a long period before the water unloads at the surface. This is because some of the air may be pushed out into the formation, causing two-phase flow problems that can create future well production issues.

Dual-pipe air lifting is when a larger pipe is put down the well, and a smaller air pipe is placed inside the first pipe. The air pipe does not extend below the larger pipe so the air is released out of the air pipe and lifts the water up through the larger pipe. No aerated water comes in contact with the well screens or casing in this method. This method is good for wells which need moderate levels of sediment removed and also minimizes the potential for air intrusion into the formation which can cause two-phase flow issues. The benefit of both of these methods is that water can consistently be produced from the well with no pump. Water with high amounts of sediment can cause significant damage to pumps, but air lifting has no moving parts in the well itself.

HIGH-PRESSURE WATER JETTING

High-pressure water jetting is a descriptive name for the method that use high-pressure water to induce water circulation in the well. Think of a spinning pressure washing being used to clean the inside of the well. Jets positioned perpendicular to the casing used as the jetting tool allow the high-pressure water to be applied directly to the screened sections of the well. Since this process results in flow outward, this process has to be followed by a development process that then reverses the flow into the well so that materials dislodged during jetting can be removed from the well.

OVER-PUMPING

Over-pumping is the most cost-saving way to clean the well; however, it can only be used after some initial development has been conducted to remove the larger suspended and/or deposited materials in the well. Water is pumped out of the well at a rate higher than the well can sustain. This causes the water to move through the gravel pack at a higher velocity than during normal pumping. The higher velocity water cleans the gravel pack, and sediment that cannot be removed by this higher velocity water is not likely to be moved during normal pumping. This method is used at the end of the development process when the large grain sediments, which can damage or destroy a pump, have largely been cleaned from the well.

LWS is very experienced in well completion and development techniques to assist with improving the efficiency of wells. If you plan on installing a well or have issues with your current one(s), do not hesitate to contact us at 303-350-4090, or email us.