DRILLING ENGINEERING CHAPTER # 1 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 Service companies Types of Wells (1) Wildcat Well: to discover new petroleum reservoir. (2) Development Well: exploit a known reservoir. Geological Group: recommends wildcat location. Reservoir Engg. Group: recommends development Drilling Group: designs and cost estimate. Tool pusher Driller Ass. Driller Derrickman (monkey board) 2-3 rotary helpers (floormen – or – rough necks) Motor man Rig mechanics Types of Wells... Rig electrician Company man Roust abouts Head roust about is the crane operator Mud engineer Casing crew Cementing service Legal Group: secures drilling rights Surveyors: establish and stake well location Drilling Contractor (Bid basis) Cost per Foot – drilling in area is routine. Cost per Day – unknown area Location Preparation Water Wells Types of Wells... • South Louisiana marshlands: inland barge • Canadian Arctic Islands: man-made ice platform • Extensive storage & Supply • Manpower: Contractor Operator Service Company Consultants 1.1 Types of Drilling Rigs 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: Surface location (land, inland water, offshore) Estimated maximum hole depth Horsepower requirements Cost Availability As can be imagined, the selecting of drilling and workover rigs is best accomplished by use of good, sound judgement and engineering experience. Rigs Marine Land Bottom FLoating Conventional Mobile Support Semi/ Drill ship Jacknife Portable Submersible Mast (Small) (Deeper) Platform Barge Jackup Self - Tendered Contained Common Types of Drilling Rigs 1. Land 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. 2. Inland Barges 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. 3. Submersible Rigs 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. 4. Jack-up Rigs 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. 5. Semi-Submersible 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. 6. Drill Ships 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. 7. Structure Rigs 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 • Rotary table rotates the drill string Downward force applied to the bit Cuttings are lifted to the surface by circulating a fluid down the drill string. Main Component Parts of a Rotary Rig are:- 1. Power System 2. Hoisting System 3. Fluid Circulating System 4. Rotary System 5. Well Control System 6. Well Monitoring System A Rotary Drilling Rig 1.2 Rig Power System Most power consumed by : hoisting system and fluid circulation Not used at same time Total power requirements 1000 – 3000 hp Old days steam Now internal combustion diesel engines types (1) diesel- electric type (electric motors), (2) direct-drive type (gears- chains) depending on power method. Power-System Performance Characteristics Are stated in terms of: 1. Output horse power 2. Torque 3. Fuel consumption for various engine speeds P = T = 2N.F.r (1.1) Where, P = shaft power (hp) = 2N, Angular velocity of the shaft (engine speed), rad/min T = output torque (lb-ft) N = Rev./min Power-System Performance Characteristics …... Overall power efficiency determines the rate of fuel consumption (Wf) at a given engine speed. Heating values (H Btu/lbm) of various fuels for internal combustion engines are shown in Table 1.1. Fuel Density (lbm/gal) Heating Value H(Btu/lbm) Diesel 7.2 19,000 Gasoline 6.6 20,000 Butane 4.7 21,000 Methane -- 24,000 • Heat energy to the engine Qi 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: P= T 7,539.8(1740) ft lbf / min = 397.5 hp 33,000 ft lbf / 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 wf is wf = 31.5 gal/hr (7.2 lbm/gal) 1hour 60 min utes = 3.78 lbm/min The total heat energy consumed by the engine is given by Eq. 1.2: Qi= wf H 3.78lbm / min(19,000 Btu / lbm)(779 ft lbf / Btu) 33,000 ft lbf / min/ hp = 1,695.4 hp. Thus, the overall efficiency of the engine at 1,200 rpm given by Eq. 1.3 is P 397.5 Et = 0.234 or 23.4% Answer Qi 1695.4 1.3 Hoisting System Function: Used to lower or raise drill strings, casing string and other subsurface equipment into or out of hole. Principal Components: 1. Derrick and substructure 2. Block and tackle 3. Draw works 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: 1. Crown block 2. Travelling block 3. Drilling line Components of the hoisting system Principal Function: To provide a mechanical advantage which permits easier handling of large loads. Load supported by travelling block Load imposed on the draw works W M Ff 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 W Mi = n W /n 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 Vf Vb n Vf Vb h Ph ( nF f ) (V f / n ) E 1 no friction Pi Ff V f Power efficiency is W E actual system Ff n Tension in the fast line W Ff (1.7) Eh 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 W W 1 E En Fd W W (1.8b) En n En fast dead 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. Calculate (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. Solution: (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. W 300,000 Ff 44,590lbf En 0.841(8) (ii) The maximum hook horsepower available is Ph = E.I = 0.841 (500) = 420.5 hp (iii) The maximum hoisting speed is given by 33,000 ft lbf / min 420.5hp P hp vb h = 46.3 ft/min W 300,000lbf To pull a 90-ft stand would require 90 ft t 1.9 min 46.3 ft / min (iv) The actual derrick load is given by Eq. 1.8b 1 E En Fd W En 1 0.841 0.841(8) (300,000) = 382,090 lbf 0.841(8) (v) The maximum equivalent load is given by Eq. 1.9 n4 84 Fde W (300,000) 450,000lbf n 8 (vi) The derrick efficiency factor is Fd 382,090 F 450,000 0.849 or 84.9% Answer Ed de Drawworks Provide the hoisting and braking power required to raise or lower the heavy strings of the pipe. Principle Parts • The drums • The brakes • The transmission • The catheads 1.4 Rotary System Main Parts: 1. Swivel 2. Kelly 3. Rotary Drive 4. Rotary Table 5. Drill Pipe 6. Drill Collar 1. Swivel: Supports the weight of the drillstring and permits rotation i.e. Bail and Gooseneck. 2. Kelly: 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. Rotary System…... 3. Slips: During making up a joint slips are used to prevent drillstring from falling in hole. 4. Rotary Drive: Provides the power to turn the rotary table. * Power Sub: can be used to connect casing. 5. Drill Pipe: Specified by (a) Outer Diameter (b) Weight per foot (c) Steel grade (d) Range Length Range Length (ft) 1 18 to 22 2 27 to 30 3 38 to 45 Rotary System…... * 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. 6. Drill Collar: Thick walled heavy steel pipe used to apply weight to the bit. * Stabilizer Subs : Keep drill collars centralized. * Capacity : Volume per unit Length. Ap 2 d = Capacity of pipe (1.13) 4 Aa (d 2 d12 ) = Capacity of annulus 2 (1.14) 4 As (d1 d 2 ) = Displacement 2 (1.15) 4 Rotary System…... Capacity and displacement nomenclature Rotary System…... 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. Solution: For field units of feet and barrels, Eq. 1.13 becomes 2 2 gal bbl 12in d 2 Ap d in. 3 ft 1,029.4 bbl / ft 4 231in. 42 gal Rotary System…... 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 4.2762 0.01766 bbl ft 1,029.4 And the capacity of the drill collars is 2.752 0.00735 bbl ft 1,029.4 The number of pump cycles required to circulate new mud bit is given by 0.01776(7,000) 0.00735(500)bbl 719cycles. 0.1781 bbl cycle Rotary System…... Similarly, the annular capacity outside the drillpipe is given by 9.8752 52 0.0704 bbl ft 1,029.4 And the annulus capacity outside the drill collars is 9.8752 82 0.0326 bbl ft 1,029.4 The pump cycles required to circulate mud from the bottom of the hole to the surface is given by 0.0704(7,000) 0.0326(500) 2,858cycles Answer 0.1781 bbl cycle Components of the rotating system 1.5 Circulating System Components: 1. Mud Pumps 2. Mud Pits 3. Mud Mixing Equipment 4. Contaminants Removal Equipment Pumps: Reciprocating Positive Displacement Piston Pumps. • Two-Cylinders - Duplex (Double Acting Forward-Backward) • Three-Cylinders - Triplex (Forward only Single Acting) Duplex Triplex Heavy Light Bulky More Compact High Output Pressure Lower Pulsation Without Pulsation Require more Maint. Cheaper to Operate Therefore majority of new pumps are Triplex. Circulating System…... Advantages (1) Ability to move high solid content fluids (2) Ability to move large particles (3) Ease to operation and maintenance (4) Reliability (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. • Shallow portion both are used. • Deeper portion one is used. Circulating System…... Components of the circulating System. Circulating System…... Circulating System Circulating System…... Pump Displacement (1) Double Acting Figure 1.25 (a) dr = Piston rod diameter dL= Liner diameter Ls= Stroke Length (Stroke = one complete pump revolution). Forward Stroke Volume Displaced = (/4) dL2 Ls 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%? Solution: 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 Circulating System…... (2) Triplex Acting Figure 1.25(b) 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 1. Hydraulic Power 2. Maximum Pressure 3. Maximum Flowrate P q PH (1.12) 1714 PH = Pump Pressure, hp ∆P = Increase in pressure, psi q = Flow rate (gal/min) ∆P cannot more than 3500 psi Circulating System…... 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. 4. Swivel 5. Kelly Go over EXAMPLE 1.3. Circulating System…... Contaminant Removal 1. Shale shaker for coarse rock cuttings 2. Hydrocyclones and decanting centrifuge for fine particles. 3. Degasser 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. 5. Use Foam. 1.6 Well Monitoring System Parameters displayed 1. Depth 2. Penetration rate 3. Hook Load 4. Rotary Speed 5. Rotary Torque 6. Pump Rate 7. Pump Pressure 8. Mud Density 9. Mud Temperature 10. Mud Salinity 11. Gas content of mud 12. Hazardous gas content of air 13. Pit Level 14. Mud Flow Rate. * Centralized well monitoring system * Mud Logger * Subsurface well-monitoring and data telemetry systems (mud pulser). 1.7 Well Control System Function: Prevents the uncontrolled flow of formation fluids from the wellbore. Kick: Flow of formation fluids in the presence of drilling fluid (blowout). Uses: 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…... Kick Detection: a. Pit volume indicator b. Flow 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 Preventers Semi circular openings which Pipe Rams match 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…... Accumulators 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. Strip Pipe Lower pipe with preventer closed. Must be able to vary closing pressure using pressure regulating system. Drilling Spool Placed between ram preventers (1) provide space for stripping (2) flowline attached to it. Well Control System…... Kill Line conduit used to pump into the annulus. Choke Line Conduit used to release fluid Diverter Line from the annulus. Drilling Spools 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. Control Panel To operate the BOP stack. RSRRS Well Control System…... Rotating Head Seals around the kelly at top of BOP stack, used for drilling with slight surface pressure at annulus. Kelly Cock Close the flow inside kelly. Internal Blowout Preventers Prevents flow inside drill string. Adjustable Choke 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.
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