I85PREP
⌘ K
AL Well Driller study materials
AL Well Driller study resources

AL Well Driller practice questions

One question at a time. Build your AL Well Driller understanding.

First 50 of 199 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Water Well Drilling Practices and Equipment

Which drilling method uses a heavy, free-falling bit suspended on a cable to break rock by impact?

  1. Cable tool drilling Correct answer.
  2. Rotary air drilling
  3. Auger drilling
  4. Jetting

Explanation

Cable tool (percussion) drilling breaks formation by repeatedly lifting and dropping a heavy bit on a cable. The hole is cleaned with a bailer rather than by circulating fluid. Rotary and auger methods cut or grind the formation instead of crushing it by impact.

Question 2Water Well Drilling Practices and Equipment

In mud rotary drilling, what is the primary function of the drilling fluid?

  1. Provide buoyancy for the drill pipe
  2. Lubricate the drill bit bearings only
  3. Carry cuttings to the surface and stabilize the borehole wall Correct answer.
  4. Cool the drill string while it is being pulled

Explanation

Drilling mud lifts cuttings up the annulus and, through filter-cake formation and hydrostatic pressure, helps hold the borehole wall open. Cooling and lubrication are secondary benefits. The main purposes are hole cleaning and borehole stability.

Question 3Water Well Drilling Practices and Equipment

A well is to be completed in unconsolidated sand where the formation tends to cave. Which screen type is most appropriate?

  1. Perforated PVC casing without slots
  2. Louvered steel screen
  3. Wire-wound screen with a gravel pack Correct answer.
  4. Continuous-slot stainless steel screen

Explanation

In caving unconsolidated sand, a gravel pack surrounds a well screen to filter formation sand while allowing water entry. Wire-wound screens are commonly used with gravel packs because their openings can be sized to retain the gravel. The gravel pack prevents sand from moving into the well.

Question 4Water Well Drilling Practices and Equipment

What is the purpose of a packer in a water well?

  1. To filter sand from the produced water
  2. To seal off an interval of the borehole or casing Correct answer.
  3. To measure the static water level
  4. To increase the pumping rate of the well

Explanation

A packer is an expandable device that isolates a section of the borehole or casing, separating intervals for grouting, testing, or preventing cross-connection between aquifers. It does not affect pumping capacity, water-level measurement, or sand filtration. Isolation of intervals is its defining function.

Question 5Water Well Drilling Practices and Equipment

Which factor most directly determines the required wall thickness of a well casing?

  1. The depth of the well and the expected collapse pressure Correct answer.
  2. The color of the formation
  3. The pumping rate of the test pump
  4. The type of screen slot size

Explanation

Casing wall thickness must resist external collapse pressure, which increases with depth and with the hydrostatic and formation pressures. Slot size and pumping rate do not govern casing strength. Formation color has no bearing on structural design.

Question 6Water Well Drilling Practices and Equipment

During rotary drilling, a sudden loss of drilling fluid returns to the surface most likely indicates:

  1. A worn swivel
  2. An increase in mud weight
  3. A lost-circulation zone Correct answer.
  4. A plugged bit

Explanation

Loss of returns means the fluid is escaping into the formation rather than returning up the annulus, which signals a lost-circulation zone such as a fracture or highly permeable layer. A plugged bit would typically raise pump pressure while returns continue. Changes in mud weight or swivel wear would not stop returns outright.

Question 7Water Well Drilling Practices and Equipment

What is the main purpose of grouting the annular space between the casing and the borehole wall?

  1. To increase the well's yield
  2. To reduce the cost of the casing
  3. To prevent surface contamination and cross-connection between aquifers Correct answer.
  4. To make the casing easier to remove

Explanation

Annular grout seals the space around the casing so that surface water and shallow contaminated water cannot travel down the annulus, and it prevents interconnection between separate aquifers. It is a sanitary and hydraulic seal, not a yield enhancement. Grout also helps stabilize the casing.

Question 8Water Well Drilling Practices and Equipment

A driller observes that the drill string is bouncing and the rate of penetration has dropped sharply while pump pressure remains normal. Which condition is most likely?

  1. The screen has plugged
  2. The bit has encountered a hard boulder or hard rock layer Correct answer.
  3. The mud weight is too low
  4. The casing has collapsed

Explanation

Bouncing of the drill string with reduced penetration and normal pump pressure is characteristic of a hard obstruction such as a boulder or hard rock layer. The bit is chattering on a hard surface rather than cutting efficiently. Low mud weight, collapsed casing, or a plugged screen would produce different symptoms.

Question 9Water Well Drilling Practices and Equipment

Which of the following best describes the function of a drilling jar in the drill string?

  1. To circulate fluid around the bit
  2. To measure the depth of the hole
  3. To straighten the borehole
  4. To deliver an upward or downward impact to free a stuck string Correct answer.

Explanation

A jar stores energy and releases it as a sharp upward or downward blow to help free a stuck drill string. It is a recovery tool, not a measurement or circulation device. It does not correct borehole deviation.

Question 10Water Well Drilling Practices and Equipment

When setting a well screen in a gravel-packed well, the gravel should be placed:

  1. In the annular space surrounding the screen Correct answer.
  2. Above the grout seal at the surface
  3. Inside the screen before it is lowered
  4. Only below the screen

Explanation

Gravel is placed in the annulus around the screen so it forms a filter pack between the formation sand and the screen openings. This graded filter prevents formation sand from entering the well. Placing gravel elsewhere would not provide the intended sand control.

Question 11Water Well Drilling Practices and Equipment

A well is drilled to 300 ft with static water level at 60 ft. What is the pumping water level if the drawdown is 25 ft?

  1. 35 ft
  2. 85 ft Correct answer.
  3. 60 ft
  4. 25 ft

Explanation

Pumping water level equals static water level plus drawdown, measured from the reference datum. Here 60 ft + 25 ft = 85 ft. Drawdown is the difference between static and pumping levels, not the pumping level itself.

Question 12Water Well Drilling Practices and Equipment

Which drilling fluid property is most important for suspending and carrying cuttings in a mud rotary hole?

  1. Viscosity Correct answer.
  2. Temperature
  3. pH only
  4. Color

Explanation

Viscosity and gel strength govern the mud's ability to hold cuttings in suspension and transport them up the annulus. Color and temperature do not control cuttings transport. pH matters for mud chemistry but is not the primary cuttings-carrying property.

Question 13Water Well Drilling Practices and Equipment

A driller needs to seal the annulus of a well completed in a bedrock aquifer where a single grout stage from surface would be impractical due to depth. Which approach is most appropriate?

  1. Pouring dry cement from the surface
  2. Tremie grouting in stages from the bottom up Correct answer.
  3. Backfilling with drill cuttings
  4. Leaving the annulus open to the surface

Explanation

Deep annular seals are placed by pumping grout through a tremie pipe from the bottom of the interval upward, often in stages, so the grout displaces water and fills the annulus without bridging. Dry cement poured from surface can bridge and leave voids. Leaving the annulus open defeats the sanitary seal.

Question 14Water Well Drilling Practices and Equipment

Which of the following is the primary reason for developing a newly completed well?

  1. To increase the casing diameter
  2. To remove drilling mud and fines from the screen and gravel pack Correct answer.
  3. To increase the well's static water level
  4. To lower the pumping water level

Explanation

Well development removes drilling fluid, fines, and disturbed material from the screen, gravel pack, and near-well formation so the well produces clear water at its full capacity. It does not change the static water level or casing diameter. Development improves hydraulic connection to the aquifer.

Question 15Water Well Drilling Practices and Equipment

A well produces significant sand after completion even though a screen was installed. Which is the most likely cause?

  1. The screen slot size is too large for the formation Correct answer.
  2. The pumping rate is too low
  3. The casing is too thick
  4. The static water level is too high

Explanation

Sand production usually means the screen openings or gravel pack are too coarse to retain the formation particles. Slot size must be matched to the formation gradation. Low pumping rate, high static level, or thick casing would not cause sand to pass the screen.

Question 16Water Well Drilling Practices and Equipment

What does a specific capacity test of a well measure?

  1. The total depth of the well
  2. The diameter of the screen
  3. The pumping rate per foot of drawdown at steady conditions Correct answer.
  4. The static water level alone

Explanation

Specific capacity is the pumping rate divided by the drawdown, expressed as flow per unit of drawdown, and indicates well efficiency. It is computed from a pumping test, not from well depth or screen diameter. Static water level alone does not define specific capacity.

Question 17Water Well Drilling Practices and Equipment

Which drilling method is best suited to drilling a large-diameter shallow hole in unconsolidated clay and sand for a monitoring well?

  1. Reverse circulation with a large bit
  2. Cable tool with a heavy bit
  3. Hollow-stem auger Correct answer.
  4. Air rotary with a button bit

Explanation

Hollow-stem augers cut and remove unconsolidated material efficiently at shallow depths and allow sampling or well installation through the hollow stem. Cable tool and air rotary are better suited to rock or deeper consolidated formations. Reverse circulation is used for large-diameter deep holes.

Question 18Water Well Drilling Practices and Equipment

A well's pumping water level continues to decline without stabilizing during a constant-rate pumping test. What does this most likely indicate?

  1. The aquifer is being dewatered or there is boundary/leakage effects Correct answer.
  2. The pump is running at too low a speed
  3. The screen is clean
  4. The well has reached steady state

Explanation

A continuously declining pumping level under constant pumping indicates that drawdown has not stabilized, which can result from a limited aquifer, dewatering, or boundary effects. Steady state would show a stable pumping level. A clean screen would favor stabilization, not continued decline.

Question 19Water Well Drilling Practices and Equipment

What is the purpose of a sanitary seal at the top of a well?

  1. To support the weight of the pump
  2. To prevent surface water and contaminants from entering the well annulus Correct answer.
  3. To measure the water level
  4. To increase the well yield

Explanation

The sanitary seal, typically a grout or bentonite seal at the surface, prevents surface water and shallow contaminants from entering the well along the casing. It is a health-protection measure. It does not support the pump or measure water level.

Question 20Water Well Drilling Practices and Equipment

During air rotary drilling, the cuttings return to the surface mainly by:

  1. A bailer lifted on a cable
  2. A suction pump at the surface
  3. The upward flow of compressed air and entrained water Correct answer.
  4. Gravity settling in the annulus

Explanation

In air rotary drilling, compressed air injected down the drill pipe returns up the annulus carrying cuttings, often with formation water or injected foam. The air velocity provides the lifting force. Bailers and suction pumps are not used for this purpose in air rotary.

Question 21Water Well Drilling Practices and Equipment

A driller is selecting a pump for a well with a static water level of 150 ft and a pumping water level of 200 ft. Which pump setting depth consideration is most important?

  1. The pump must be set at the ground surface
  2. The pump must be set below the pumping water level with adequate submergence Correct answer.
  3. The pump must be set above the static water level
  4. The pump must be set above the pumping water level

Explanation

A submersible pump must be set deep enough to remain submerged below the pumping water level, with adequate submergence to avoid cavitation and loss of prime. Setting it above the pumping level would cause it to draw air. Setting it above the static level or at the surface would not work for a deep well.

Question 22Water Well Drilling Practices and Equipment

Which of the following best describes the purpose of a liner in a water well?

  1. To increase the pumping rate
  2. To filter formation sand
  3. To seal the annulus at the surface
  4. To line an unstable interval inside the borehole or casing Correct answer.

Explanation

A liner is installed inside the borehole or existing casing to support an unstable or caving interval. It is a structural support element, not a sand filter or surface seal. It does not by itself increase pumping rate.

Question 23Water Well Drilling Practices and Equipment

What is the main advantage of a pitless adapter in a well installation?

  1. It allows the discharge line to pass through the casing below frost depth without a pit Correct answer.
  2. It measures the pumping water level
  3. It increases the well's yield
  4. It replaces the well screen

Explanation

A pitless adapter lets the pump discharge line exit through the casing wall below frost depth, eliminating the need for a pit and protecting the line from freezing. It is a plumbing convenience and freeze-protection device. It does not affect yield or replace the screen.

Question 24Water Well Drilling Practices and Equipment

A driller observes that the borehole is deviating significantly from vertical at depth. Which factor is the most common cause?

  1. Excessive mud weight
  2. A clean screen
  3. A low pumping rate
  4. Bit walk in steeply dipping or hard formations Correct answer.

Explanation

Borehole deviation commonly results from bit walk, where the bit tends to drift in steeply dipping or alternating hard formations, and from insufficient stabilization. Mud weight, screen condition, and pumping rate do not cause deviation. Proper stabilization and drilling technique help control it.

Question 25Water Well Drilling Practices and Equipment

Which test is commonly performed to determine the yield and drawdown characteristics of a completed well?

  1. A sieve analysis of the gravel pack
  2. A constant-rate pumping test Correct answer.
  3. A water quality lab test
  4. A casing thickness measurement

Explanation

A constant-rate pumping test measures pumping rate and drawdown over time to characterize well and aquifer performance. Sieve analysis characterizes gravel gradation, water quality testing characterizes chemistry, and casing measurement checks structural dimensions; none of these determine yield and drawdown.

Question 26Water Well Drilling Practices and Equipment

Which component of a mud rotary drilling rig is responsible for removing cuttings from the drilling fluid before it is recirculated?

  1. The swivel
  2. The mud pump
  3. The shale shaker Correct answer.
  4. The kelly

Explanation

The shale shaker uses vibrating screens to separate drill cuttings from the returning drilling fluid so the mud can be recirculated. The mud pump moves fluid, the swivel allows rotation while circulating, and the kelly transmits rotation to the drill string.

Question 27Water Well Drilling Practices and Equipment

What is the primary function of a casing centralizer in a water well?

  1. To increase the weight of the casing string
  2. To allow the casing to be driven without rotation
  3. To filter sand from the produced water
  4. To keep the casing centered in the borehole Correct answer.

Explanation

Centralizers are attached to the casing to keep it centered in the borehole, which helps ensure a uniform annular space for grouting. They do not add significant weight, filter sand, or enable driving.

Question 28Water Well Drilling Practices and Equipment

Which drilling method uses a heavy, free-falling bit to break rock by impact?

  1. Air rotary drilling
  2. Cable tool drilling Correct answer.
  3. Reverse circulation drilling
  4. Mud rotary drilling

Explanation

Cable tool drilling breaks rock by repeatedly lifting and dropping a heavy bit, and the cuttings are removed with a bailer. The other methods use rotating bits and circulating fluids to remove cuttings.

Question 29Water Well Drilling Practices and Equipment

Which type of well screen is made by winding wire around a cage of longitudinal rods?

  1. Slotted PVC screen
  2. Bridge-slot screen
  3. Louvered steel screen
  4. Continuous-slot wire-wound screen Correct answer.

Explanation

Continuous-slot wire-wound screens are manufactured by winding wire around longitudinal rods, creating a precise slot opening. Slotted PVC and louvered steel screens are made by cutting or punching openings in a pipe, and bridge-slot screens are formed by punching and bridging metal.

Question 30Water Well Drilling Practices and Equipment

What is the primary function of a mud pit in a mud rotary drilling operation?

  1. To provide a water supply for the drilling crew
  2. To hold the drill pipe when it is not in use
  3. To mix cement for grouting
  4. To store and allow cuttings to settle from the drilling fluid Correct answer.

Explanation

Mud pits provide storage and allow cuttings to settle out of the drilling fluid before it is recirculated. They are not used for cement mixing, pipe storage, or as a potable water supply.

Question 31Water Well Drilling Practices and Equipment

Which of the following is a common type of drilling bit used in air rotary drilling?

  1. Button bit Correct answer.
  2. Roller cone bit
  3. Fishtail bit
  4. Drag bit

Explanation

Button bits, which have tungsten carbide buttons, are commonly used in air rotary drilling for hard rock. Drag and fishtail bits are used in soft formations with mud rotary, and roller cone bits are typically used in mud rotary or oil and gas drilling.

Question 32Water Well Drilling Practices and Equipment

What is the purpose of a J-hook or safety hook on a drilling rig?

  1. To measure the weight on the bit
  2. To prevent the traveling block from accidentally detaching from the swivel Correct answer.
  3. To guide the drill string into the hole
  4. To connect the mud hose to the standpipe

Explanation

A J-hook or safety hook is a locking device that secures the traveling block to the swivel and prevents accidental detachment. It does not measure weight, guide the drill string, or connect the mud hose.

Question 33Water Well Drilling Practices and Equipment

A driller is using a mud rotary rig and notices that the drilling fluid is becoming thicker and returning fewer cuttings. Which adjustment is most appropriate?

  1. Stop circulating and continue drilling dry
  2. Add more cuttings to the mud
  3. Decrease the mud flow rate
  4. Increase the mud flow rate and adjust viscosity Correct answer.

Explanation

Thickening mud and poor cuttings returns indicate the mud is carrying too much solids or has improper viscosity. Increasing flow and adjusting viscosity helps improve cuttings transport and cleaning. Decreasing flow or stopping circulation would worsen the problem.

Question 34Water Well Drilling Practices and Equipment

When drilling with a cable tool rig, what is the purpose of adding water to the hole?

  1. To cool the bit
  2. To lubricate the drill line
  3. To create a slurry that helps suspend and remove cuttings Correct answer.
  4. To increase the weight of the string

Explanation

In cable tool drilling, water is added to mix with cuttings and form a slurry that the bailer can remove. It is not primarily for cooling, adding weight, or lubricating the line.

Question 35Water Well Drilling Practices and Equipment

A driller is installing a well screen and wants to maximize open area while maintaining strength. Which screen type generally provides the highest ratio of open area to total area?

  1. Perforated casing
  2. Slotted PVC screen
  3. Louvered steel screen
  4. Continuous-slot wire-wound screen Correct answer.

Explanation

Continuous-slot wire-wound screens are designed with a continuous wire winding that provides a high percentage of open area while maintaining structural strength. Slotted PVC, louvered steel, and perforated casing typically have lower open-area ratios.

Question 36Water Well Drilling Practices and Equipment

What is the primary purpose of a blowout preventer (BOP) in water well drilling?

  1. To filter the drilling fluid
  2. To measure the flow rate of the well
  3. To control pressure and prevent uncontrolled flow from the well Correct answer.
  4. To prevent the drill pipe from dropping into the hole

Explanation

A BOP is a safety device that seals the wellbore to control formation pressure and prevent blowouts. It does not support the drill pipe, measure flow, or filter mud.

Question 37Water Well Drilling Practices and Equipment

A driller is using a roller cone bit and notices that the rate of penetration has decreased while the pump pressure has increased. What is the most likely cause?

  1. The mud weight is too low
  2. The bit bearings are new
  3. The drill string is too short
  4. The bit is balling up with cuttings Correct answer.

Explanation

Bit balling occurs when cuttings adhere to the bit, reducing penetration rate and increasing pump pressure. New bearings, low mud weight, or a short drill string would not cause these symptoms.

Question 38Water Well Drilling Practices and Equipment

Which of the following is a typical function of a drilling fluid in a mud rotary well?

  1. To cool and lubricate the bit Correct answer.
  2. To generate electricity for the rig
  3. To provide structural support to the casing
  4. To increase the weight on bit

Explanation

Drilling fluid cools and lubricates the bit and drill string, in addition to carrying cuttings and stabilizing the borehole. It does not add weight on bit, support casing, or generate electricity.

Question 39Water Well Drilling Practices and Equipment

A driller is using a drag bit in a hard formation and experiences rapid wear. Which change is most appropriate?

  1. Switch to a roller cone or button bit Correct answer.
  2. Increase the rotary speed
  3. Decrease the mud flow rate
  4. Add more weight on bit

Explanation

Drag bits are designed for soft formations and wear quickly in hard rock. Switching to a roller cone or button bit, which are designed for harder formations, is the appropriate change. Increasing speed or weight would accelerate wear.

Question 40Water Well Drilling Practices and Equipment

What is the purpose of a casing shoe in water well construction?

  1. To connect two joints of casing
  2. To guide the casing through the borehole and protect the casing end Correct answer.
  3. To filter sand from the water
  4. To measure the depth of the well

Explanation

A casing shoe is attached to the bottom of the casing to guide it through the borehole and protect the casing end during installation. It does not join casing, measure depth, or filter sand.

Question 41Water Well Drilling Practices and Equipment

Which drilling method is most suitable for drilling a deep well in hard crystalline bedrock with minimal water use?

  1. Air rotary drilling Correct answer.
  2. Auger drilling
  3. Mud rotary drilling
  4. Cable tool drilling

Explanation

Air rotary drilling uses compressed air to remove cuttings and is well suited for hard bedrock, especially where water is scarce. Cable tool is slow, mud rotary requires large water volumes, and auger drilling is limited to shallow unconsolidated formations.

Question 42Water Well Drilling Practices and Equipment

A driller is experiencing lost circulation while drilling with mud. Which of the following is a common method to regain circulation?

  1. Add lost circulation material to the mud Correct answer.
  2. Increase the mud weight
  3. Reduce the mud flow rate
  4. Increase the rotary speed

Explanation

Lost circulation material (LCM) is added to the mud to plug the openings in the formation and restore circulation. Increasing mud weight or rotary speed would likely worsen the loss, and reducing flow may not solve the problem.

Question 43Water Well Drilling Practices and Equipment

What does the term 'make-up torque' refer to in drill pipe handling?

  1. The torque applied to tighten a threaded connection Correct answer.
  2. The torque needed to pull the drill string
  3. The torque applied to the drawworks brake
  4. The torque required to rotate the bit

Explanation

Make-up torque is the torque applied to tighten a threaded connection to the proper specification. It is not the torque to rotate the bit, pull the string, or apply the brake.

Question 44Water Well Drilling Practices and Equipment

A driller is using a mud rotary rig and notices that the borehole is caving in. Which action is most likely to stabilize the borehole?

  1. Increase the mud density and viscosity Correct answer.
  2. Increase the rotary speed
  3. Reduce the mud flow rate
  4. Decrease the mud density

Explanation

Increasing mud density and viscosity helps to support the borehole wall and prevent caving. Decreasing density or reducing flow would reduce support, and increasing rotary speed does not address the cause.

Question 45Water Well Drilling Practices and Equipment

Which of the following is a primary consideration when selecting a drilling method for a specific site?

  1. The experience of the drilling crew
  2. The distance to the nearest town
  3. The geological formations to be penetrated Correct answer.
  4. The color of the drilling rig

Explanation

The geological formations are a primary factor because different methods are suited to different materials and conditions. Rig color, crew experience, and distance to town are not primary technical considerations.

Question 46Water Well Drilling Practices and Equipment

A driller is using a mud rotary rig and observes that the drill string is sticking. Which of the following is the most likely cause?

  1. Too much water in the mud
  2. Low mud viscosity
  3. Excessive rotary speed
  4. Differential pressure sticking Correct answer.

Explanation

Differential pressure sticking occurs when the drill string is pulled against a permeable formation by the pressure difference between the mud column and the formation. Excessive rotary speed, low viscosity, or too much water are not typical causes of sticking.

Question 47Water Well Drilling Practices and Equipment

In air rotary drilling, what is the purpose of injecting a foaming agent into the air stream?

  1. To reduce the noise of the compressor
  2. To increase the penetration rate in hard rock
  3. To cool the bit more effectively
  4. To help lift cuttings in wet or unconsolidated formations Correct answer.

Explanation

Foam is used in air rotary drilling to help lift cuttings when water is present or formations are unconsolidated, improving hole cleaning. It is not primarily for cooling, increasing penetration in hard rock, or reducing noise.

Question 48Water Well Drilling Practices and Equipment

A driller is using a mud rotary rig and the mud pump pressure suddenly drops while the flow rate remains constant. What is the most likely cause?

  1. A break or leak in the circulating system Correct answer.
  2. The mud viscosity has increased
  3. The drill string is stuck
  4. The bit is plugged

Explanation

A sudden drop in pump pressure with constant flow often indicates a break or leak in the circulating system, such as a hole in the drill pipe or a failed connection. A plugged bit would increase pressure, and increased viscosity would also increase pressure.

Question 49Water Well Drilling Practices and Equipment

When drilling with a cable tool rig in unconsolidated sand, which tool is used to remove the cuttings from the hole?

  1. Tremie pipe
  2. Auger
  3. Core barrel
  4. Bailer Correct answer.

Explanation

A bailer is a long cylinder with a valve at the bottom used to remove cuttings and slurry from a cable tool hole. Augers are used in auger drilling, core barrels in coring, and tremie pipes for placing concrete or grout.

Question 50Water Well Drilling Practices and Equipment

A driller is using a mud rotary rig and the borehole is deviating from vertical. Which factor is most likely to cause this deviation?

  1. High mud flow rate
  2. Excessive weight on bit in a steeply dipping formation Correct answer.
  3. Low mud viscosity
  4. Using a new bit

Explanation

Excessive weight on bit combined with steeply dipping formations can cause the bit to follow the formation dip, leading to deviation. Low viscosity, high flow rate, or a new bit are not typical causes of deviation.