Wellpoint
What is a WellPoint:
A well point is a hole that is blown with water pressure to extract shallow ground water from the water table below the surface of the ground. They usually can reach a maximum depth of about 10m depending on your particular area and ground water profile. WellPoint's are sufficient for the irrigation of small to medium sized residential gardens. It consists of a pump that is situated above ground to suck up the water. It is more cost effective and quicker to install than a borehole due to the shallower depths needed. Sometimes the water yield from one well-point will not be enough to run your irrigation system and so a second /third or fourth well-point is blown. These points are then connected together to work as one system. The whole process takes about 2-4hrs to install.
PROS
High penetration rate, fairly cheap.
Easy soil and groundwater sampling during drilling.
Possible to measure yield estimate at selected depth in the formation.
CONS
Can only be used in sandy conditions with a high water table.
No use of drilling mud.
Water level fluation may cause well to dry up in very dry weather conditions as water table lowers.
Rotary Mud Drilling
What is a Rotary Mud Drilling:
In the direct-mud rotary drilling method, the borehole is advanced by rapid rotation of a drill bit mounted on the end of the drill rods. The bit cuts and breaks the material at the bottom of the hole into small pieces (cuttings). The cuttings are removed by pumping drilling fluid (water or water mixed with a fluid enhancer, such as bentonite) down through the drill rods and bit and up the annulus between the borehole and the drill rods. The drilling fluid also serves to cool the drill bit and stabilize the borehole wall, to prevent the flow of fluids between the borehole and surrounding earth materials, and to reduce cross-contamination between aquifers.
Direct-mud rotary drilling offers a number of advantages. It is a very fast and efficient means of drilling. Efficient rigs can produce several thousand feet of hole per day. The direct-mud rotary method can reach to several thousand feet in depth and create hole diameters greater than 48 inches. The method is adaptable to a wide range of geologic conditions. Only exceptionally large, poorly stabilized boulders or karst (cavernous) conditions are unsuited for direct-mud rotary drilling.
Sediment sampling is broadly supported in direct-mud rotary drilling. Standard split-barrel and thin-wall sampling are available in poorly lithified materials, while a broad range of coring equipment is supported for consolidated rock. Hydrologic conditions have little effect on direct-mud rotary drilling; operations usually are unhindered by the presence of ground water. Direct-mud rotary drilling readily supports the telescoping of casings to successively smaller sizes to isolate drilled intervals and to protect lower geologic units from contamination by previously drilled, contaminated upper sediments.
Direct-mud rotary drilling has some inherent disadvantages for monitoring well installation. If the drilling mud is not carefully engineered, drilling fluids may invade permeable zones, compromising the validity of subsequent monitoring well samples from those intervals. The mud cake necessary to hole stability usually will interfere to some extent – by ionic exchange – with the analysis of monitoring well water samples. Organic compounds that commonly are added to drilling fluids also may interfere with chemical and physical tests on sediment samples. Poorly engineered drilling fluids may produce difficult-to-remove mud cakes that inhibit the flow of fluids to the well. Relatively large volumes of cuttings and drilling fluids may provide containment problems, and must be disposed of properly.
At sites being monitored for hydrocarbons, inherently complex rotary rigs may introduce grease and oil to the monitoring system. Mud pumps, water swivels, rotary drives, rod connections and drilling fluid components all may contribute hydrocarbons inadvertently to the system, despite the best decontamination/degreasing efforts. When water or other materials are introduced to the drill hole, those materials must be sampled and analysed as control samples.
Despite these obstacles, direct-mud rotary drilling can be the best alternative, especially for deep wells or wells completed into well-lithified rocks. When direct-mud rotary methods are used, hole diameters should be 3 inches to 5 inches larger than the outer diameter of the well casings to allow effective placement of filter and sealing materials. Two-inch diameter monitoring wells should, therefore, be installed within 5.5-inch or larger holes.
PROS
High penetration rate.
Drilling operation requires a minimum amount of casing.
Rapid mobilization and demobilization.
CONS
Use of a drilling fluid, both in terms of sample contamination and water management (in the case of water-based fluids and air injected by gasoline compressors).
Circulation of drilling fluid may be lost in loose/coarse formations, hence making difficult to transport drill cuttings.
Difficult to collect accurate samples, i.e. a sample from a discrete zone since the cuttings accumulate at surface around the rim of the borehole.
ODEX Percussion Down-The-Hole Hammer
What is ODEX Percussion Down-The-Hole Hammer (Odex, Stratex, and Tubex are trade names):
ODEX is an adaptation of the air-operated down-the-hole hammer. It uses a swing-out eccentric bit to ream the bottom of the casing. The percussion bit is a two-piece bit consisting of a concentric pilot bit behind which is an eccentric second bit that swings out to enlarge the hole diameter. Immediately above the eccentric bit is a drive sub that engages a special internal shouldered drive shoe on the bottom of the ODEX casing. The ODEX is thus pulled down by the drill stem as the hole is advanced. Cuttings blow up through the drive sub and casing annulus to a swivel conducting them to a sample collector or onto the ground.
Drilling limitations are essentially the same as for the down-the-hole hammer method.
PROS
Rapid removal of cuttings.
No use of drilling mud.
High penetration rate, especially in resistant rock formation (e.g. basalt).
Easy soil and groundwater sampling during drilling.
Possible to measure yield estimate at selected depth in the formation.
Advantageous in unconsolidated formations with a high risk of caving (this is probably the most important feature).
CONS
Practically restricted to unconsolidated formations.
Relatively a more expensive method.
Down-The-Hole Hammer Drilling Method
What is Down-The-Hole Hammer Drilling Method:
The down-the-hole hammer drill is a pneumatically operated bottom-hole drill that efficiently combines the hitting action, similar to that of cable tool drilling, with the turning action of rotary drilling. The pneumatic drill can be used on any standard rotary rig with an integral or auxiliary air compressor of sufficient capacity. It is used for fast and economical drilling of medium to extremely hard formations. Fast penetration results from the air piston blows transmitted directly to the bit, so practically no energy is wasted in chewing up cuttings. A straight hole is assured by short, rapid blows that minimise the effect of dipping and broken formations. Down-the-hole hammer drilling is by far the fastest method of penetration in hard rock material. The bit is turned slowly (10 to 15 RPM) by the same method that rotates the drill bit in the mud or air drilling operation.
PROS
Rapid removal of cuttings.
No use of drilling mud.
High penetration rate, especially in resistant rock formation (e.g. basalt).
Easy soil and groundwater sampling during drilling.
Possible to measure yield estimate at selected depth in the formation.
CONS
Restricted to semi-consolidated to consolidated formations.