CHAPTER # 1. DRILLING ENGINEERING. Rotary Drilling Rigs. Objective To familiarize the student with (1) the basic rotary drilling equipment and operational procedures. (2) introduce the student to drilling cost evaluation . Drilling Team Large companies vs. small Specialized skills
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CHAPTER # 1
Rotary Drilling Rigs
To familiarize the student with
(1)the basic rotary drilling equipment and operational procedures.
(2)introduce the student to drilling cost evaluation.
(1)Wildcat Well:to discover new petroleum reservoir.
(2)Development Well:exploit a known reservoir.
Types of Wells...
Drilling and workover rigs come in a variety of shapes and sizes with each having its own characteristics suited for a particular job. Although there are many factors to be considered in selecting the best rig for the job, a few are especially critical. They are:
Portable Mast (Small)
Common Types of Drilling Rigs
As the name implies, these rigs are primarily used on land; however, some have been transported offshore for structure rig assignments. Most land rigs have to be transported to location in sections, but some are self-contained, permanently mounted on trucks. On location they are usually set up on a board mat with a substructure of 8 to 40 feet high, and a few are capable of drilling holes to 30,000+ feet.
Inland Barges are composed of two types:
a.Barge mounted rigs
This type rig is capable of drilling in water depths from 0 to 12 feet. After being towed on location, the rig’s hull is filled with water until it rests on bottom.
b.Posted barge mounted rigs
These type rigs have an upper deck supported by posts from the lower hull. The deck contains all drilling equipment and accommodations. Posted barges are capable of drilling in water depths from 0 to 20 feet. The rig is towed on location and the lower hull filled with water to secure it on bottom.
These rigs are towed on location and are capable of working in water depths from 18 to 70 feet. They are composed of an upper deck and lower hull connected by beams. On some types a large bottle, or something similar, is located on each corner of the rig for stability. These bottles, as well as the lower hull itself, are filled with water to set the rig on bottom and stabilize against movement.
These rigs are normally towed on location, but a few are self-propelled. They are composed of an upper deck supported by either three or more legs attached to mats or spud cans and are capable of working in water depths from 30 to 350 feet. These mats or cans rest on the ocean floor with the deck jacked up into drilling position. There are two common types of jack-up rigs; Bethlehem and Letourneau. The former uses stabilized column legs attached to mats while the latter uses three, truss-type legs mounted on spudcans.
These rigs can be towed on location, or some types are self-propelled. They are capable of drilling in water depths of 20 to 2,000+ feet. The rig itself remains stationary in the drilling position by a series of anchors (usually two connected at each corner of the rig) positioned on the ocean floor at a distance away from the rig. It should also be noted that some Semis can be used as a submersible rig.
Drill ships are self-propelled drilling vessels capable of drilling in water depths of 18 to 2,000+ feet. There are two basic types of drill ships - one that positions itself with anchors and one that uses dynamic positioning.
Structure rigs are mounted on a fixed platform with all drilling equipment secured on deck. The rig itself is capable of changing positions on the structure; however, the structure is permanently based and designed to last many years. Structures are capable of being set in water depths of 10 to 850+ feet. Structure set-ups usually follow a successful exploratory program in order that many development wells can be drilled from one location. These wells are almost always directional.
Rotary Drilling Process
Main Component Parts of a Rotary Rig are:-
3.Fluid Circulating System
5.Well Control System
6.Well Monitoring System
A Rotary Drilling Rig
1.2 Rig Power System
hoisting system and fluid circulation
Power-System Performance Characteristics
Are stated in terms of:
1.Output horse power
3.Fuel consumption for various engine speeds
P= T = 2N.F.r (1.1)
P=shaft power (hp)
=2N, Angular velocity of the shaft (engine speed), rad/min
T=output torque (lb-ft)
Power-System Performance Characteristics …...
FuelDensity (lbm/gal)Heating Value H(Btu/lbm)
Qi = Wf.H (hp) (1.2)
Et = P /Qi = Energy Output / Energy Input (1.3)
Et = overall power system efficiency
Example 1.1: A diesel engine gives an output torque of 1,740 ft-lbf at an engine speed of 1,200 rpm. If the fuel consumption rate was 31.5 gal/hr, what is the output power and overall efficiency of the engine?
Solution:The annular velocity, , is given by
=2(1,200) = 7,539.8 rad/min.
The power output can be computed using Eq. 1.1:
= 397.5 hp
Since the fuel type is diesel, the density is 7.2 lbm/gal and the heating value H is 19,000 Btu/lbm (Table 1.1). Thus, the fuel consumption rate is wfis
= 3.78 lbm/min
The total heat energy consumed by the engine is given by Eq. 1.2:
Qi= wf H
wf= 31.5 gal/hr (7.2 lbm/gal)
= 1,695.4 hp.
Thus, the overall efficiency of the engine at 1,200 rpm given by Eq. 1.3 is
= 0.234 or 23.4% Answer
1.3 Hoisting System
Used to lower or raise drill strings, casing string and other subsurface equipment into or out of hole.
1.Derrick and substructure
2.Block and tackle
Functions of Derrick:
1.Provides vertical height required to raise sections of pipe.
2.Rated according to their ability to withstand compressive loads and (wind loads)
Components of Block and Tackle:
To provide a mechanical advantage which permits easier handling of large loads.
M= Mechanical advantage
F = tension in the fast line
The ideal mechanical advantage that assumes no friction in the block and tackle can be determined from a force analysis of the travelling block.
n Ff= W
Input power of block and tackle = pi
Pi = Ff Vf(1.5)
Ff = draw works load
Vf = velocity of fast line
Ph = output power of the hook load
Pn = W.Vb(1.6)
W = travelling block load
Vb = velocity of travelling block
Power efficiency is
Tension in the fast line
Eq. 1.7 is used to select drilling line size.
Fd= W + Ff + Fs(1.8a)
Fd= load applied to the derrick
Fs= tension in the lead line
Example 1.2: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 500hp. Eight lines are strung between the crown block and traveling block.
(i) the static tension in the fast line when upward motion is impending,
(ii) the maximum hook horsepower available,
(iii) the maximum hoisting speed,
(iv) the actual derrick load
(v) the maximum equivalent derrick load, and
(vi) the derrick efficiency factor.
Assume that the rig floor is arranged as shown in Fig 1.17.
(i) the power efficiency of n=8 is given as 0.841 in Table 1.2. The tension in the fast line is given by Eq. 1.7.
(ii) The maximum hook horsepower available is
Ph = E.I = 0.841 (500) = 420.5 hp
(iii) The maximum hoisting speed is given by
= 46.3 ft/min
(iv) The actual derrick load is given by Eq. 1.8b
To pull a 90-ft stand would require
= 382,090 lbf
(v) The maximum equivalent load is given by Eq. 1.9
(vi) The derrick efficiency factor is
0.849 or 84.9% Answer
Provide the hoisting and braking power required to raise or lower the heavy strings of the pipe.
1.4 Rotary System
Supports the weight of the drillstring and permits rotation i.e. Bail and Gooseneck.
Square or Hexagonal to be gripped easily. Torque is transmitting through kelly bushings. Kelly saver sub is used to prevent wear on the kelly threads.
During making up a joint slips are used to prevent drillstring from falling in hole.
Provides the power to turn the rotary table.
* Power Sub:can be used to connect casing.
Specified by (a) Outer Diameter
(b) Weight per foot
(c) Steel grade
(d) Range Length
118 to 22
227 to 30
338 to 45
* Tool Joint:Female is called Box.
Male is called Pin.
* Upset :Thicker portion of the pipe.
* Internal upset:Extra thick.
* Thread Type:Round, tungsten carbide hard facing.
Thick walled heavy steel pipe used to apply weight to the bit.
* Stabilizer Subs : Keep drill collars centralized.
* Capacity :Volume per unit Length.
= Capacity of pipe (1.13)
= Capacity of annulus (1.14)
= Displacement (1.15)
Capacity and displacement nomenclature
Example 1.4:A drillstring is composed of 7,000 ft of 5-in., 19.5-lbm/ft drillpipe and 500 ft of 8-in. OD by 2.75-in ID drill collars when drilling a 9.875-in. borehole. Assuming that the borehole remains in gauge, compute the number of pump cycles required to circulate mud from the surface to the bit and from the bottom of the hole to the surface if the pump factor is 0.178 bbl/cycle.
For field units of feet and barrels, Eq. 1.13 becomes
Using Table 1.5, the inner diameter of 5-in., 19.5 lbm/ft drillpipe is 4.276 in.; thus, the capacity of the drillpipe is
And the capacity of the drill collars is
The number of pump cycles required to circulate new mud bit is given by
Similarly, the annular capacity outside the drillpipe is given by
And the annulus capacity outside the drill collars is
The pump cycles required to circulate mud from the bottom of the hole to the surface is given by
Components of the rotating system
1.5 Circulating System
3.Mud Mixing Equipment
4.Contaminants Removal Equipment
Reciprocating Positive Displacement Piston Pumps.
High Output PressureLower
Require more Maint.Cheaper to Operate
Therefore majority of new pumps are Triplex.
(1)Ability to move high solid content fluids
(2)Ability to move large particles
(3)Ease to operation and maintenance
(5)Ability to operate over wide range of pressure s and flow rates by changing the diameters of the pump liners and pistons.
Overall Pump Efficiency =Mechanical Efficiency x Volumetric Efficiency
Em= Mechanical Efficiency ~ 90%
Ev= Volumetric Efficiency ~ 100%
Two Circulating pumps are installed on the rig.
Components of the circulating System.
Figure 1.25 (a)
dr = Piston rod diameter
dL= Liner diameter
Ls= Stroke Length (Stroke = one complete pump revolution).
Forward Stroke Volume Displaced = (/4) dL2Ls
Backward Stroke Volume Displaced = (/4) (dL2 - dr2 ) Ls(for one Cylinder)
Total Volume =Fp= 2 Ls(/4) (2LL2 - Lr2 ) . Ev(1.10)
(for two Cylinders)
Fp= Pump factor or pump displacement cycle.
Example 1.3:Compute the pump factor in units of barrels per stroke for a duplex pump having 6.5-in. liners, 2.54-in. rods, 18-in. strokes and a volumetric efficiency of 90%?
The pump factor for a duplex pump can be determined using Eq 1.10:
Fp= 2 Ls(/4) (2LL2 - Lr2 ) . Ev
= (/2) (18) [ 2(6.5)2 - (2.5)2] . (0.9)
= 1991.2 in.3 /stroke
or = 0.2052 bbl/stroke.Answer
Fp= 2 (/4) dL2 Ls. Ev(1.11)
q=flow rate = Fp . N
(Where N = no. of cycles per unit time)
Pumps are rated for
PH = Pump Pressure, hp
∆P = Increase in pressure, psi
q = Flow rate (gal/min)
∆P cannot more than 3500 psi
Flow conduits between pump and drill string include:
1.Surge chamber (Pulsation Damper)
2.4 or 6 inch heavy-walled pipe connecting the pump to a pump manifold located on the rig floor.
3.Standpipe and rotary hose.
Go over EXAMPLE 1.3.
1.Shale shaker for coarse rock cuttings
2.Hydrocyclones and decanting centrifuge for fine particles.
Gas as a drilling Fluid (Air, Natural gas)
1.Penetration rate is higher than water especially when formation is strong and extremely low K.
2.Water flow is a problem.
3.Isolate by injecting
(a) Low Viscosity Plastic
(b) Silicon Tetrachloride
(c) Using Packers
4.Min. annular velocity is 3000 ft/min for injection pressure.
1.6 Well Monitoring System
11.Gas content of mud
12.Hazardous gas content of air
14.Mud Flow Rate.
*Centralized well monitoring system
*Subsurface well-monitoring and data telemetry systems (mud pulser).
1.7 Well Control System
Prevents the uncontrolled flow of formation fluids from the wellbore.
Flow of formation fluids in the presence of drilling fluid (blowout).
1.Detect the Kick
2.Close the well at the surface.
3.Circulate the well under pressure to remove formation fluids and increase density.
4.Move drillstring under pressure.
5.Divert flow away from rig personnel and equipment.
Kick Detection During Drilling Operation
Well Control System…...
a.Pit volume indicator
c.Hole fill up indicator (during tripping)
d.Count the pump strokes.
BOP (Blow Out Preventer)
Multiple BOP’S used in series: BOP Stack
Ram PreventersSemi circular openings which
Pipe Ramsmatch diameter of pipe
Blind Rams :Closes the hole, no pipe present.
Shear Rams:Blind rams that shear the pipe.
Working press: 2000, 5000, 10000, 15000 psig.
Annular Preventers (Bag-type):Rubber Ring
BOPE:Closed hydraulically or using screw-type locking.
Well Control System…...
High pressure hydraulic system used to close the BOP.
* Fluid Capacity : 40, 80 120 gal.
* Max. Operating Pressure : 1500-3000 psig.
* has a small pump independent of rig power.
Lower pipe with preventer closed. Must be able to vary closing pressure using pressure regulating system.
Placed between ram preventers
(1)provide space for stripping
(2)flowline attached to it.
Well Control System…...
conduit used to pump into the annulus.
Choke LineConduit used to release fluid
Diverter Linefrom the annulus.
Must be large enough to allow next casing to be put in place without removing the BOP.
Casing Head (Braden Head)
Attached to BOP, welded to the first string of casing cemented in the well.
To operate the BOP stack. RSRRS
Well Control System…...
Seals around the kelly at top of BOP stack, used for drilling with slight surface pressure at annulus.
Close the flow inside kelly.
Internal Blowout Preventers
Prevents flow inside drill string.
Used during Kick circulation, controlled from a remote panel on the rig floor.
Sufficient pressure must be held against the well by the choke so that the bottomhole pressure in the well is maintained slightly above the formation pressure.
* Working Press Systems: 2000,3000,5000,10000,15000 psig.