Wellbore Drilling: Process, Rig Systems & Equipment

Course Assessment

• Course assessment includes quizzes (5%), Test 1 (12%), Test 2 (13%), Project (10%), Laboratory (10%), and Examination (50%).
• A minimum of 90% attendance is required to sit for the final examination.
• Passing the course requires a minimum of 40% marks in coursework, final examination, and a combination of both.

Recommended Textbooks

• A.T. Bourgoyne Jr. et al., Applied Drilling Engineering, SPE Textbook Series Volume 2, 2nd Edition, SPE (1991).
• H. Rabia, “Well Engineering & Construction.”
• Steve Devereux, Drilling Technology in Non-Technical Language, 1st Edition, Pennwell Corporation (2001).
• J. P Nguyen, Drilling, TECHNIP (1996).

Course Learning Outcome

• The lecture contributes to fulfilling course learning outcome CLO-1: describing drilling process, drilling rig systems, and equipment used to drill a well.

Learning Outcomes

• Describe the wellbore drilling process.
• Discuss the components of a rotary drilling rig.
• Perform simple calculations relating to these components.

The Rotary Drilling Equipment

• Rotary drilling is the conventional method in the oil and gas industry.
• A well is drilled through the rotating action of a drill bit with applied downward force.
• New pipe lengths are added as drilling progresses.
• Cuttings are transported to the surface via drilling mud.
• A rotary drilling rig is used for drilling.

Components/Systems of a Rotary Drilling Rig

• The major components/systems of a rotary drilling rig include:
  • Power Generating System
  • Hoisting System
  • Mud Circulating System
  • Rotary System
  • Well Control System
  • Data Acquisition & Well Monitoring System

The Power Generating System

• This system includes the fuel storage, engines, and generators.
• Modern rigs use an internal combustion engine with diesel.
• Rigs require a lot of power, ranging from 1000 – 7000 or more horsepower (HP).
• Diesel engines are compounded to provide the required horsepower.
• The two largest power consuming systems are hoisting and mud circulating.

The Power Generating System Performance

• Key performance characteristics include output horsepower, torque, and fuel consumption.
• Formula for output horsepower: 𝑃𝑜 = (2πNT)/33000, angular velocity = 2πΝ
• Formula for fuel consumption in lb/hr: 𝑄𝑓 = 48.46 (NT/EH).
• Engine efficiency calculation: Efficiency (%) = (Output power / Input power) * 100.
• Input power of an engine: 𝑃𝑖 = (𝑄𝑓 H) / 2545
  • T = output torque in ft – lbs
  • E = Engine Efficiency
  • N = Engine rotary speed in RPM
  • Qf = fuel consumption rate
  • H = fuel heating value in BTU/lb

Example 1: Diesel Engine Output Power and Efficiency

• A diesel engine has an output torque of 1,870 ft-lbf at 1,100 rpm.
• It burns 30 gal/hr of diesel with a heating value of 19,000 BTU/lbm and a density of 7.2 lbm/gal.
• The fuel consumption is 216 lbm/hr.
• Output power is 391.7 hp.
• Input power is 1612.6 hp.
• Engine efficiency is 24.3%.

Example 2: Drilling Rig Fuel Consumption

• A rig uses three diesel engines with an average running speed of 900 rpm.
• The average output torque is 1,610 ft-lb, with an engine efficiency of 40%.
• The heating value of diesel oil is 19,000 BTU/lbm.
• Daily fuel consumption is 924 gal/day.

Example 3: Fuel Cost Calculation

• An engine runs at 1,800 rpm with 3,000 ft-lb of output torque and 30% efficiency.
• Diesel cost is RM 2.05/gal, the weight is 7.2 lb/gal, and the heating value is 19,000 BTU/lb.
• The fuel cost is RM 3136.5/day.

Exercises

• Problems involving the calculation of wheel angular velocity, power output, overall efficiency, torque, drill string velocity, and distance traveled using diesel engines on rigs.

The Hoisting System

• The hoisting system raises, lowers, and suspends the drill string.
• It also lifts casing/tubing into the well.
• Two major functions:
  • Making a connection (adding a new joint of drillpipe).
  • Making a trip (moving the drillstring out of the hole).

Components of the Hoisting System

• Key components include the Derrick and substructure, Block and tackle, and Drawworks.
• The derrick provides vertical height to raise sections of pipe.
• It is rated based on its ability to withstand compressive loads and wind loads.

Drawworks

• The drawworks is a winch that reels the drilling line in or out, moving the traveling block.
• It consumes the most energy from the power system.

Principal Function of Block & Tackle

• Provides a mechanical advantage for handling large loads.
  • M = W/Ff (Mechanical advantage = Load supported / Load imposed on the drawworks)
  • n Ff = W , Mi = W / (W /n) = n
• The ideal mechanical advantage assumes no friction.

Components in Block and Tackle System

• The input power is supplied by the drawworks.
• The output is the hookload.
• Formulas include:
  • Power = Force * (distance / time) = Force * Velocity
  • Input Power (P) = Fastline force (Ff) * Fastline Velocity (Vf)
  • Output Power (Po) = Hookload (Fh) * Travelling block Velocity (Vtb)
  • Efficiency (E) = (Po / Pi) = (Fh * Vtb) / (Ff * Vf)
  • Velocity of traveling block (Vtb) = Velocity of fastline (Vf) / Number of drilling lines (n)
• Fh = Hookload
• n = Number of lines.
• Ff = Fastline force

Example: Hoisting System Calculation

• A hook is hoisted at 40 ft/min, with a drill pipe weight of 16.77 lb/ft, a drill collar weight of 94.6 lb/ft, a drill collar length of 300 ft, a well depth of 9000 ft, and 10 drilling lines.
• Efficiency is 78%
  • Fastline velocity is 400 ft/min.
  • Hookload is 174,279 lb.
  • Load at drawworks is 22,343.5 lb.
  • HP of drawworks: 270.8 horsepower

Classwork

• A rig must hoist a load of 300,000 lbf.
• The drawworks can provide an input power to the block and tackle system as high as 500 hp.
• Eight (8) lines are strung between the crown block and traveling block, with efficiency for n = 8 lines to be 0.841
  • The static tension in the fast line when upward motion is impending, Ff=44,590lbf
  • The maximum hook horsepower available is Ρη = 420.5 hp
  • The maximum hoisting speed is Vb= 46.3 ft/min

Mud Circulating System

• This allows for circulation of mud down through the drill string and up through the annular space.
• Components include mud tanks, mud pumps, mud mixing equipment, and solids control equipment.
• Mud pumps of the circulation system and the drawworks are the two largest power consumers on the rig.

Mud Tanks

• A mud tank is a sizable storage container that holds mud on the rig.
• Mud tanks are constructed from welded-up steel plates/tubes.
• Catwalks with guard rails allow workers to inspect the drilling fluid safely.
• Mud tanks are classified as Active tanks and Reserve tanks.

Active Tank

• An active tank holds the mud during drilling and this volume depends on keeping the well hole full. -This tank can pick up mud , contain the cleanest fluid and holds all characteristics of mud.

Reserve Tank

• A reserve mind is not an active park of the drilling process, but it has critical functions.
• This includes the storage of excess mud and heavy mud for emergencies
• For crew members to mix different types of mud.

Mud Pumps

• If gas is used as the drilling mud, an air compressor pumps the gas.
• There are at least two mud pumps connected by a mud manifold.
• When drilling large diameter holes, the two pumps are connected in parallel for high flow rate.
• When drilling smaller holes, only one pump is necessary and the other is a backup.
• Mud pumps must provide the flowrate required.
• Flow rates are selected by the Drilling Engineer based on well stability, annular velocity, type of annulus flow, drilling with a downhole motor, and lag time.

Pathway of a Drilling Mud

• Mud flows in the following sequence:
  • From mud tank to mud pump
  • From mud pump to stand pipe
  • From stand pipe to rotary hose
  • From rotary hose to swivel
  • From swivel into hollow drill string
  • From drill string to drill bit
  • From drill bit nozzles to annular space
  • From annular space to surface
  • From surface to solids control equipment
  • From solids control equipment to the suction tank

Types of Rotary Rig Pumps

• These are reciprocating positive displacement pump units.
• Two types:
  • Duplex have two liners and move fluids on the forward and backward strokes (double acting).
  • Triplex have 3 liners and move fluids only on the forward stroke (Single acting pump).
• Duplex pumps are heavy, have pulsation, are bulky, and have high output pressure and require further maintenance.
• Triplex pumps are light, have no pulsation, are compact, have lower output pressure and are cheaper to operate.

Pump Formulas

• Theoretical volume of fluids displaced by a mud pump calculations:
  • Single-acting pump (Triplex pump): 𝑉𝑡 = (π / 4) 𝐷𝐿² 𝐿𝑆 𝑁𝑐
  • Double acting pump (Duplex pump): 𝑉𝑡 = (π / 4) 𝑁𝑐 𝐿𝑠 (2𝐷𝐿² − 𝐷𝑟²)
• VTheoretical volume of mud displaced by pump (in³/stroke)
• 𝐷𝐿= liner or piston diameter (inches)
• 𝐿𝑆 = stroke length (inches)
• 𝑁𝑐 = number of cylinders (2 for duplex & 3 for triplex)
• 𝐷𝑟= rod diameter (inches)
• Actual volume: 𝑉𝑎𝑐𝑡𝑢𝑎𝑙 = 𝑉𝑡ℎ ∗ 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦
• Pump hydraulic horsepower: HHP = (PpQ)/1714 (Q = flowrate in gals/min; P = Pump delivery pressure (psi);

Rotary System

• The rotary system causes the drill bit to rotate at the bottom of the wellbore.
• It includes the swivel, Kelly, rotary table, drill pipe, and drill collar.

Components of the Rotary System

• Swivel supports the weight of the drillstring, permits drillstring rotation, and allows mud to be pumped while the string is rotating.
• Kelly transfers rotary movement from the rotary table to the drillstring.
• A Kelly cock prevents backflow of fluids through the Kelly to the swivel.
• The top drive rotates the drill string from top whereas a kelly system at the rig floor with the help of a rotary table
• The rotary table transmits rotation to the drillstring and suspends pipe weights during trips.

Well Control System

• Its primary function is to prevent any flow of formation fluid into the wellbore while drilling.
• Three control barriers for controlling a well during drilling:
  • Primary well control (drilling mud)
  • Secondary well control (blowout preventer - BOP)
  • Tertiary well control (drilling a relief well)
• Other equipment include kelly cock, adjustable choke, and inside BOPs.

Blowout Preventer (BOP) Identification

• A blowout preventer stack is identified by a designation, such as 5M - 13 5/8 – SRRA:
  • A = annular type blowout preventer.
  • R = single ram-type preventer.
  • Rd = double ram-type preventer
  • Rt = triple ram-type preventer
  • S = drilling spool with side outlet connections
  • M = 1000 psi rated working pressure.

Data Acquisition & Well Monitoring System

• Consists of all devices to monitor, analyze, record, display, and retrieve information.
• The parameters of prime concern are hookload, WOB, pump discharge pressure, rotary speed, rate of penetration, rotary table torque, and pump strokes per minute, grouped together on a pressurized explosion-proof panel.

Understand the wellbore drilling process and rotary drilling rig systems. This lesson covers equipment used in drilling. Also covers course assessment, required attendance and passing criteria.