Drilling is used in
- site assessments for the collection of soil and water samples
- installation of water monitoring wells
- installation of producing wells
Drilling method depends on:
- purpose of drilling program
- geology
- drilling depth
- site accessibility
- available equipment
- cost
What does make footage mean?
Drilling as fast as they can
What does cavings mean?
Pieces of sides of borehole will collapse into hole
What does lost circulation mean?
Drilling fluids (muds) leave the borehole and enter (lost in) a subsurface formation
What does mud cake mean?
(Filter cake) build up of solids from the mud into the borehole wells from the mud across from K zones
What does cuttings mean?
(Chips) very small pieces of rocks that have been ground up by the drill bit to create the borehole
What does lag time mean?
Time between when the chips are cut down hole and when they arrive at surface
What does tripping in/out mean?
- time it takes to pull the bit out of the hole (tripping out)
- time it takes to put the bit in the hole (tripping in)
What does fishing mean?
Drillers or loggers have lost a tool (down hole and are trying to retrieve it)
Explain Driven wells
Installed by hand using a sledge hammer, percussion or a
Driver head
For shallow, small diameter drilling in unconsolidated seds
Explain Direct push wells
Hydraulic units, mounted in trucks, push a steel core barrel (d~6cm) into the ground
For shallow drilling in unconsolidated seds
Explain auger wells
Don’t need drilling fluid
3 types:
- rotary bucket
- Hollow stem auger
- Solid stem auger
Also hand augering
Explain a rotary bucket
Large diameter (d~90cm) cylindrical bucket with cutting blades at its base where it contacts soil
~80 x 90 cm casing sections can then be lowered into the angered hole
For unconsolidated material
Explain a Hollow stem auger
Hollow stem pipe encircled by ‘flights’
Auger is driven by a hydraulic rig with a rotary head
How can a hollow stem auger help with soil sampling
- Sample between borehole and auger
2. Sample through the augers hollow stem
Explain solid stem auger
Solid stem pipe encircles by flights
Driven by hydraulic rig with a rotary head
Auger must be removed before you can put in a monitoring well
Sed must be cohesive
Explain cable tool wells
Percussion drilling, shudder rigs
- earliest form of drilling
- involves lifting, dropping and rotating a heavy drill bit in end of cable
-you have to periodically stop and remove cuttings
Cuttings removed as a slurry
Large hole (d is 40-60cm)
In cable tool wells what do you do if no water is naturally entering hole from surroundings
A little water is added to mix with the chips to bring them to surface as a slurry
Explain drilled wells
-use drilling fluid
-2 types: 1. Conventional
Rotary and 2. Reverse rotary
Based in direction of mud flow in borehole
Explain conventional rotary
Rotation of but on the end of a drill pipe at high speeds
- drilling fluids pumped down through the drill pipe and out through holes in drill bit
- fluids pick up cutting and bring them to surface through annulus
Subtypes based on fluid used (I.e. water, mud air,chemical foams)
Purpose of drilling fluid in drilled wells is to:
- Lubricate bit
- Cool bit
- Bring chips to surface. A) don’t need to stop drilling(saves money). B) bit doesn’t get stuck in down hole (jamming)
- mud cakes over K brines. A) stop lost circulation. B) stops further contamination of formation
Downsides to drilling muds
- Mudcake buildup -> seals off low yield aquifer
(You may even miss it while drilling) - P mud»_space;> P formation
- > will not push formation fluids from borehole
- > won’t get representative sample
Common drilling bits
- Drag bits
- unconsolidated seds - Roller cones (most common is tricone)
- rocks - Diamond core drill bits
- hollow pipe with industrial diamonds (boarts) on it’s cutting edge
