“Flowing artesian” wells mean:
A flowing artesian well is “controlled” when:
Artesian conditions arise when there is a movement of groundwater from a recharge area under a confining formation to a point of discharge at a lower elevation. An example of this is a natural spring, or in the example of the drilling industry, a flowing water well.
Groundwater recharge areas may consist of higher elevation lakes or swamps/muskegs, or exposed sand and gravel formations, fractured bedrock, or other permeable formations. The confining formations may consist of: clay formations, glacial till deposits, impervious bedrock formations. Groundwater flow conditions can vary to a great degree within local areas depending upon local geological conditions.
Flowing artesian wells are generally controlled by the use of a sealed surface casing and the use of control valves on the production casing. As seen in the Figure 1, the use of multiple pressure relief fittings may be required to gain control of a flowing well. With these fittings, cement grout can be pumped between the production and surface casing against the artesian flow that may be moving upward toward the surface.
Some knowledge of the artesian pressure and artesian formation depth(s) is required, so that when pumping the grout, one does not overpressure the confining formation and cause a condition known as a “Frac- Out”. A Frac-Out (also known as hydraulic fracture) may occur close to the well or at some distance away, and may result in artesian flows coming to surface in unexpected locations.
A commonly used “rule of thumb” calculation for confining ground weight could be: 1 ft. of overburden material will hold back approximately 1 psi of formation pressure.
Example of pressure in an artesian condition: Artesian flow encountered at 100 ft. below ground elevation, artesian pressure measured at 10 psi at surface. The weight of the water column is 100ft / 2.41 ft/psi = 43.29 psi. The weight of the ground is about 100psi. Ground weight minus column weight is 56.71 psi. Ground pumping pressures nearing 56 psi have the potential of causing a Frac-Out condition.
Grout can be pumped from 10+ psi to 70 psi (safety factor) to fill voids between the production casing and the ground formations and to seal the annulus between the production casing and surface casing. The rate at which an artesian formation will accept grout will vary due to the available porosity of the geological unit. For example, coarse, clean gravels will accept pumped fluids at a faster rate than fine grained sand because of the pore capacity.
Different methods of drilling require different strategies for installing the surface casing.
In this method, the hole is drilled open, surface casing is installed, and then grout is pumped in to displace fluids in the annulus between the casing and the geological formation. To calculate the volume of grout required to seal the surface casing and the formation, the volume of the open hole is first calculated, and then the enclosed volume of the surface casing is subtracted from the total volume of the hole. The open hole must be drilled to a suitable depth in a competent formation (such as clay or bedrock) in order to provide an adequate surface seal. Creating a suitable seal with the cement grout minimizes the potential for artesian groundwater pressures to cause water to flow outside of the casing. When the desired depth of casing has been installed in the open hole with a flow fitting welded to the side, the casing installation is typically completed in the following manner:
In this method of drilling, surface casing can be placed in a shorter length of time than using the Mud Rotary Method. Similar to driving a steel pipe piling, a seal is formed between the geological formation and the surface of the steel pipe being driven.
Some knowledge of artesian groundwater flows, pressures, and geological conditions within the local area is a valuable asset in determining the amount of surface casing that will be required to provide a suitable seal.
Installation of surface casing for a flowing artesian well is typically undertaken in the following manner:
In all drilling programs planning is essential for the successful completion of the project. Knowledge of the geology of the area, required materials for the project and equipment to do the job are required for a successful completion of a drilling program.
When a cable tool drill rig is used to drill a flowing artesian well, surface casing can be installed using either the mud rotary method or the air rotary method whichever is desired. One method may be more practical than the other, dependent upon the drilling equipment utilized to complete the well. As in all drilling programs, preplanning and execution of good drilling practices aid in the successful completion of the project.
British Columbia has over 357 thousand square miles of land area within the provincial boundaries. Within this land mass there are varied geological formations. There are some recorded flowing artesian formations and many more to be discovered as drilling continues. One of the least explored areas within the province is on the east side of the Rocky Mountains in the north-east section of the province (Peace River District). Artesian conditions will likely be encountered while drilling for the Oil & Gas industry, since much of the rural population in the area relies on either surface water dugouts, or cisterns with hauled water for their water supply.
Drilling programs conducted by the Oil & Gas sector vary greatly. These include: seismic exploration, water injection supply wells, and soils investigations for pipeline river crossings, drive pile installation programs, and slope stability assessments. While conducting these types of drilling programs, flowing artesian conditions have been encountered.
Many of these holes have been drilled without the use of surface casing, making the control of water flows much more difficult. Inflatable packers and bentonite have been used to control and stop flows with some success, but the locations and geological conditions at most of those sites have not been recorded, and the long term success or failure of such seals is uncertain. There are potential detrimental effects on the environment, and on the groundwater resource when drilling in artesian conditions without the appropriate equipment and materials.
The ultimate impact on the environment and the groundwater resource will likely continue to be debated for some time to come.
Sometimes in drilling programs there are formations that are encountered that are not expected. They may be flowing artesian formations or formations containing natural gasses such as carbon dioxide, methane, or hydrogen sulphide (H2S).
Encountering these gasses creates some very unique problems. Carbon dioxide gasses, in sufficient quantities, can create a low oxygen atmosphere and create a safety hazard. Methane gasses, in quantities, can create an explosive atmosphere as well a fire hazard. H2S in very low percentages can cause suffocation and possibly death. The possibility of encountering these formations increases when working on the east side of the Rockies (e.g. the Peace River area) in northern B.C. where shale gas resources are known to exist.
This article has been prepared in good faith to assist water well professionals working in flowing artesian environments. Every well is unique and requires site-specific planning. Any use, interpretation, or reliance on the information presented herein is at the sole risk of that party, and neither the author nor the BC Ground Water Association accept any liability for injury or damage resulting thereof.
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