diseÑo bombeo mecÁnico parte 1

7/27/2019 DISEO BOMBEO MECNICO PARTE 1

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Sucker Rod Pump

Beam PumpDesign

30/10/2013 1BOMBEO MECNICO


2/72

Beam Pump Surface Components

Prime Mover

Gear reducer

Pumping unit Polished rod

Transformer

Control BoxElectricMotor

Polished RodStuffing Box

Tubing

Sucker Rods

Pump



3/72

Surface Components

Prime Mover Electric or internal combustion engine

Provides driving force as a rotary movement of themotor shaft

Gear reducer Reduces the high rotational speed of the motor to

the required pump speed Increases the torque (the ability of a force to

cause a body to rotate about a particular axis.)



4/72

Surface Components

Pumping unit Transforms the rotational movement of the

gearbox shaft into a reciprocatingmovement at the tip of the walking beam.

Polished Rod

connects the walking beam with the suckerrod string and provides sealing surface atthe wellhead



5/72

Downhole Components

Rod String Responsible for transmitting the reciprocating

movement of the polished rod to the downholepump.

Pump contains the traveling valve and the standing valve

admit fluids from the annulus to the pump barrel transfer momentum to the fluids to be produced

through the tubing



6/72

Schematic of PumpSucker Rods

Plunger

Traveling Valve

Standing Valve

Upstroke Downstroke

Working Barrel



7/72

Upstroke

Traveling valve closes due to thepressure of the fluids inside the tubing

The rising rod string pushes the plungerand fluids above it upwards.

Standing valve opens and casing fluids

enter.



8/72

Downstroke

Increased pressure forces standingvalve shut.

Traveling valve opens allowing fluidabove the plunger.



9/72

Design Methods

Simplified Method Developed for Shallow wells

Simple (reliable) equations for operationalparameters

API RP 11L Valid at increased depth where simplified

method fails Successfully used in the oil industry for

more than 20 years



10/72

Beam Pump System Performance



11/72

Reference

Gabor Takacs: Modern Sucker-Rod

Pumping- PenWell Books



12/72

Schematic of a Beam Pump Unit



13/72

Beam Pump Configurations

Conventional



14/72


Mark II



15/72


Air Balanced



16/72


Torque Master



17/72

Pumping Unit Designations



18/72

Design Methods

Mathematical solution for the movementof the sucker rod string

Most accurate method Requires the use of a numerical simulator

We will confine ourselves to API RP 11L www.api.org



19/72

Design and Analysis

Prediction of the operating conditions isof vital importance for the design of new

installations and the analysis of existingones Polished rod loads

Downhole stroke length Torques



20/72

Polished Rod Load

The weight of the rod string, Wr

The buoyant force

Mechanical and fluid frictionUsually neglected

Dynamics force on the string

The load of the fluid being produced



21/72

Polished Rod Load



22/72

Design Prequisites

Polished rod loads

Downhole stroke length

Torques



23/72

Peak Polished Rod Load

(PPRL) Maximum

(downward) force on

beam Occurs when the

rod is moving upand lifting liquid

F

rW

TD

DD

DLF ,

ULF ,



24/72

Loads neglecting acceleration

Simplified Model Weight of sucker rod string in air

Pressure force of fluid above plunger

Ap plunger area, ft2

Arod

area of thedeepest sucker rod, ft2

rW

c

rodpTL

D,Lg

AAgDF



25/72

Upward force on plunger due topressure from casing fluid:

DD depth to dynamic fluid level, ft Measured using an Echometer

c

DTpL

U,Lg

DDgAF

Loads neglecting acceleration

Simplified Model



26/72

Dynamic Load SimplifiedMethod

Mass of the rod times its acceleration

Concentrated point load

Acceleration factor of Mills (dimensionless)

S Polished rod stroke length, inches N pumping speed in SPM (strokes per minute)

70500

2NS



27/72

Peak Polished Rod LoadSimplified Method For Conventional Units

In most texts, the last term is neglectedto compensate for unknown friction

losses Fluid Load:

c

TrodL

c

DpL

rg

DgA

g

DgAWPPRL

1

c

DpL

og

DgAF



28/72

Minimum Polished Rod LoadMPRL

F

BrW ,

TD

DD

Occurs when rod ison the downstroke

Fluid flowing throughtraveling valve

Rod buoyed up bysurrounding fluid



29/72

Force Balance - Downstroke

MPRL = Buoyant rod weight DynamicForces

Buoyant rod weight :

Dynamic Forces (Simplified method) :

rod

LrodrW

r

W



30/72

Minimum Polished Rod Load

Simplified Method

SGW

WMPRL

r

rod

Lr

128.01

1

SGfluid specific gravity



31/72

Example

Find the minimum and maximumpolished rod loads for a 5000 ft rod

string composed of 42.3% of , 40.4%of 5/8 and 17.3% of rods.Plunger

size is 1.5 and the fluid level is at 4800

ft. Pump speed is 10 spm, stroke lengthis 120 and the specific gravity of thefluid is 0.95.



32/72

Solution

Determine the total rod weight,Wr From table,

Acceleration Factor

lbf6375

726.0173.0135.1404.0634.1423.05000

rW

17.0

70500

101202



33/72

Table for rod properties



34/72

Solution

Fluid load on Plunger

Peak Polished rod load

lbf3487

480024

5.1

4.6295.0

2

c

DpL

og

DgA

F

lbf10964

1

or FWPPRL



35/72

Solution

Minimum Polished Rod Load

lbf4513

17.095.0128.016375128.01

SGWMPRL r



36/72

Peak Torque Sizing Motor Crankshaft torque

Rod string requirements

Counterweight requirements

Assumptions Pumping unit balanced

MPRL and PPRL occur when the torque

factor maximum

in-lbf4

)(S

MPRLPPRLPT



37/72

Plunger Stroke Length

Surface and downhole stroke lengthsdiffer considerably

Sucker rod string is elastic Tubing string is also elastic

Definition: Plunger stroke is the travel of

the pump plunger relative to thestanding valve. (Units: inches)



38/72

Plunger Stroke Length Fluid load alternately

acts on the travelingvalve and on the

standing valve Upstroke traveling

valve

Downstroke standing

valve Additional stretch due

to acceleration



39/72

Plunger Stroke Length

Low pumping speeds (negligibledynamic loads)

Unanchored tubing

Anchored tubing (no tubing stretch)

erand etare rod and tubing stretch in inches

trp eeSS

rp eSS



40/72

Rod Stretch

Erelastic constant,(see Table)

L

length of the rodsection, ft

Fo- fluid load onplunger, lbf

orr LFEe



41/72

Fiberglass Rods



42/72

Tubing Stretch

Etelastic constant, (see Table) Ltlength of the tubing section, ft Fo- fluid load on plunger, lbf

ottt FLEe



43/72

Dynamic Stretch (inch)

Due to inertial forces Maximal at the endpoints of the stroke

Cause an attritional elongation in therod string

Plunger Overtravel

Simplified model concentrated load

261036.1 Leo



44/72

Total Stretch

Unanchored tubing

Anchored tubing

otrp eeeSS

orp eeSS



45/72

Tapered rod/tubing

If the rod and/or tubing strings aretapered, we must sum the stretches on

each section

i

i

ioLEFe



46/72

Example

Calculate the plunger stroke length for a5000 ft rod string composed of 42.3% of

, 40.4% of 5/8 and 17.3% of rods.Use the results from the previousexample for loads.



47/72

Solution

Elongation of the rod Sum elongations over each section

inch4.21

173.01099.1404.01026.1423.010833.0

50003487

666

i

ririor LeFe



48/72

Solution

Elongation of the tubing

Plunger overtravel

inch9.3

3487500010211.0 6

te

inch8.5

17.050001036.1 26

oe



49/72

Solution

Plunger stroke

inch5.100

8.59.34.21120

pS



50/72

Pump Displacement

From downhole stroke length, the dailyvolumetric pump displacement is given

by

PD pump displacement in RB/d

d plunger diameter (inch)

21166.0 dNSPD p



51/72

Example

Calculate the pump displacement forthe previous example.

Solution

RB/d264

5.1105.1001166.0

1166.0

2

2

dNSPD p



52/72

Question:Does a Sucker rod pump

produce fluid only on theupstroke?



53/72

Rod string design

Should we use a single-diameter rod? Rods near the plunger carry the smallest

loads (the fluid weight) Rods near the surface carry the fluid

weight as well as the weight of all rodsbelow

Use a tapered string Rod diameter decreases with depth



54/72

Ideal Tapered String

Tapered to have nostress hot spots Stress = load/area Want uniform stress

Rod strings come indiscrete diameters Uniform stress

unattainable

Equalize stressesin rod strings.

Ideal Tapered String



55/72

Rod Size

At a given position, the minimumapplicable rod diameter must support

the maximum tensile stress at thatposition. Tensile stresses are cyclic.

Maximum on upstroke Minimum on downstroke

Must account for metal fatigue



56/72

Tensile Strength For small loads, a metal rod will stretch an

amount proportional to an applied load, andreturn to its original dimensions when theload is removed. Hookes Law Applies until the elastic limit

Beyond the elastic limit, additional load willpull the rod apart.

Tensile Strength - The quantity of stressneeded to overcome a materials resistanceto structural failure.



57/72

Metal Fatigue

Weakened condition induced inmetal parts of machines, vehicles,

or structures by repeated stressesor loadings, ultimately resulting infracture under a stress muchweaker

than that necessary tocause fracture in a singleapplication.



58/72

Fatigue Endurance Limit

The maximum stress level at which theequipment will operate under cyclic

loading conditions for 10 millioncomplete cycles.

Affected by operating conditions Salt water

Hydrogen Sulfide


Goodman Diagram


59/72

Goodman Diagram



60/72

Rod Stresses

Maximum Stress, psi

Minimum Stress, psi

2max

4rd

PPRLS

2min4

rd

MPRL

S



61/72

Maximum Allowable Stress

To prevent rod breakage from metalfatigue, we need maximum allowable

stress

SF service factor T tensile strength of the rod

SFST

Sa

min5625.04



62/72

Service Factors

Maximum tensile strength (T) for API grades C and D

are 90000 and 115000 psi respectively.



63/72

Tapered String Design

Attempt to equalize stress distributionsin the rods

Several approaches available Simplified Method

Wests method

Neelys method/API Method



64/72

Simplified Method

Goal Keep maximum rod stresses at avalue based on a percentage of the

tensile strength of the rod material. Set the maximum stress at the top of

each taper section equal.



65/72

Example 7/8 6/8 - 5/8



66/72

Simplified Method



67/72

Simplified Method

Gives reasonable rod life for shallowwells.

Using this method, practically all rodbreaks are due to fatigue Still applied to high-strength E-rods

Maximum allowed stress is constantregardless of stress range (50,000 psi)



68/72

Example

Design an API 65taper rod string usingE rods for a pump setting depth of 5000

ft and a pump size of 2.5 inch. Assumewe are pumping water.

Note: a API 65 refers to two strings, the

top with size 6/8 inch and the bottomwith 5/8 inch.API 64 will consist of 6/8, 5/8, 4/8 rods.



69/72

Solution

From formulas

Length of 5/8 section: 1621 ft

Length of section: 3379 ft

%42.32

5.208.767.762

1

R



70/72

Solution

Checking whether the rod design willmeet maximum allowable stress

requirements Weight of rod string:

lbf5521634.13379

lbf1840135.11621

86

85

W

W



71/72

Solution

Fluid Load

Maximum stresses (neglectingacceleration)

lbf10625500024

5.2

4.62

2

oF

psi40690442.0/5521184010625

psi40600307.0/184010625

8/6max,

8/5max,

S

S



72/72

Solution

Minimum stresses

Since E Rods are rated at a maximum

allowable stress of 50000 psi regardlessof stress range, the design is safe.

psi16650442.0/55211840

psi5990307.0/1840

8/6min,

8/5min,

S

S

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