Unit - 3 WELL DESIGN Design characteristics – Design of wells .pptx

Well design is the process of planning and constructing a well to effectively extract groundwater while maintaining efficiency, longevity, and water quality. A properly designed well maximizes yield, minimizes operational costs, and reduces the likelihood of contamination or well failure. The design process involves selecting appropriate well dimensions, materials, and construction techniques based on the specific hydrogeological conditions of the site.

Key Considerations in Well Design:
Hydrogeological Conditions: The design of the well depends on the characteristics of the aquifer, including:

Aquifer type (confined, unconfined, or semi-confined).
Depth to water-bearing formations.
Hydraulic conductivity and transmissivity.
Groundwater quality.
Purpose of the Well: The design varies depending on whether the well is for:

Water supply (domestic, industrial, agricultural, or municipal use).
Monitoring (to track groundwater levels or contamination).
Recharge (artificially recharging the aquifer).
Expected Pumping Rate (Yield): The size and structure of the well should be designed to achieve the required yield. Larger yields require larger well diameters and deeper penetration into the aquifer.

Well Depth: The depth of the well is determined by the depth of the aquifer and the water level. It is crucial to reach the most productive water-bearing zones to ensure sufficient water supply.

Components of Well Design:
1. Well Diameter
Definition: The inside diameter of the well casing, typically expressed in inches.
Significance: Affects the volume of water the well can store, the size of the pump, and the efficiency of water extraction. Larger diameters allow for more water storage and easier pump installation but are more expensive.
Selection Criteria: The required flow rate (yield) and the type of pump being used.
2. Well Casing
Definition: A pipe placed inside the well bore to prevent the collapse of the borehole walls and protect the water from contamination.
Materials: Common materials include steel, PVC (polyvinyl chloride), and fiberglass.
Functions:
Prevents the contamination of the well by surface water or polluted zones.
Ensures the structural integrity of the well.
Provides a path for water flow from the aquifer to the pump.
3. Well Screen
Definition: A perforated section of the casing installed at the depth where the well intersects the aquifer, allowing water to flow into the well while preventing sand and sediment from entering.
Materials: Stainless steel, PVC, or other corrosion-resistant materials.
Slot Size: The size of the openings in the screen should be selected based on the size of the aquifer material to prevent clogging by fine sediments.
Length: Depends on the thickness of the water-bearing formation and the expected yield.
4. Gravel Pack (Filter Pack)
Definition: A layer of sand or gravel placed around the well screen to filter out fine particles from the formation and prevent clogging.

1. KONGUNADU COLLEGE OF ENGINEERING AND TECHNOLOGY (Autonomous) Department of Agriculture Engineering Course: Groundwater and Well Engineering Topic :Well By Mr. M.Sundharan , Assistant Professor, Department of Agricultural Engineering, Kongunadu College of Engineering and Technology

2. The depth and type of groundwater well you'll need depends on several factors, including: The depth of the water table in your area:  This is the distance from the ground surface to the top of the saturated zone where groundwater is found. You can usually get this information from a local well driller or Hydrogeologists. The amount of water you need:  If you only need a small amount of water for domestic use, a shallow well may be sufficient. However, if you need a large amount of water for irrigation or other purposes, you may need a deeper well. The type of soil and rock in your area:  Different types of soil and rock will affect how easily water can flow through them and how deep you will need to drill to reach the water table. Your budget:  Drilling a well can be expensive, so you will need to factor in the cost of drilling, materials, and installation when making your decision.

3. Here are the most common types of groundwater wells: Dug wells:  These are the simplest and oldest type of well. They are typically dug by hand or with a machine and can be up to 30 feet deep. Dug wells are not a good choice in areas with contaminated soil or rock, as they are susceptible to surface water infiltration.

4. Driven wells:  These wells are created by driving a small-diameter pipe into the ground until it reaches the water table. Driven wells are typically 25 to 50 feet deep and are a good option for areas with limited space.

5. Drilled wells:  These wells are created by drilling a hole into the ground with a drilling rig. Drilled wells can be hundreds of feet deep and are the most common type of well for large water supplies .

6. DESIGN OF WELL SCREENS The design of a well screen (also known as ‘strainer’ ) involves the determination of screen length, location of the screen, percentage open area, size and shape of openings (slots), screen diameter, and the selection of screen material.

7. Important Factors Determining Well Screen Location and Length of the screen Size and Shape of Slots Screen Diameter Screen Materials

8. Types of Well screen Types of commonly used well screens: (a) V-shape continuous slot screen, (b) Louver-type screen, (c) Rectangular slot screen, and (d) Pipe-base well screen or Metallic filter point.

9. WELL CASING A well casing is a pipe inserted into a wellbore to prevent the sides from collapsing and to isolate the well from surrounding formations. It is typically made of steel, plastic, or fiberglass and is installed in sections, with each section being welded or screwed together. The space between the casing and the wellbore is then filled with cement to create a seal.

10. Prevent the wellbore from collapsing: The wellbore is often drilled through unstable formations that could collapse without support. The casing provides the necessary structural support to keep the wellbore open. Isolate the well from surrounding formations: This is important to prevent contamination of the well water by fluids from other formations. The casing also helps to prevent the well from affecting the surrounding formations. Provide a conduit for fluids: The casing allows fluids, such as water, oil, or gas, to flow from the wellbore to the surface. Protect the well from corrosion: The casing can be coated with a corrosion-resistant material to protect it from the corrosive effects of the well fluids.

11. Here are some of the most common types of well casings: Steel casing: Steel casing is the most common type of casing used in oil and gas wells. It is strong and durable, but it can be expensive and susceptible to corrosion. Plastic casing: Plastic casing is less expensive than steel casing and is more resistant to corrosion. However, it is not as strong as steel casing and may not be suitable for some applications. Fiberglass casing: Fiberglass casing is a good option for wells that are drilled through corrosive formations. It is strong and lightweight, but it can be more expensive than other types of casing.