Design of Sucker Rod Pump

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Design of Sucker Rod Pump March 28 2010 Offshore oil and gas production PE6060 Abhishek Joshi PE10M001 Pramod P ME07B028

Transcript of Design of Sucker Rod Pump

Page 1: Design of Sucker Rod Pump

Design of Sucker Rod Pump

March 28

2010Offshore oil and gas production PE6060

Abhishek JoshiPE10M001

Pramod PME07B028

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Introduction

Artificial lift is the use of artificial means to increase the flow of fluids, mostly crude oil or water from a production well. This can be achieved by a number of ways, the two well-known ones being,

1. Use of mechanical device inside the well, ex. Pump2. By injecting gas into the well to decrease the weight of the hydrostatic

column,

These measures are required in wells where there is insufficient pressure in the reservoir to lift the produced fluids to the surface.

Sucker Rod Pump

It is also known as Beam / Horse head / Thirsty bird / Nodding donkey. It is an over ground drive for a reciprocating piston pump installed in an oil well.

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A SRP converts the rotary mechanism of the motor to a vertical reciprocating motion to drive the pump shaft, and is exhibited in the characteristic nodding motion. The engineering term for this type of mechanism is a walking beam.

The five major components of a SRP are

1. the prime mover, which provides power to the system

2. the gear reducer, which reduces the speed of the prime mover to a suitable pumping speed

3. the pumping unit, which translates the rotating motion of the gear reducer and prime mover into a reciprocating motion

4. the sucker rod string, which is located inside the production tubing, and which transmits the reciprocating motion of the pumping unit to the subsurface pump

5. the subsurface pump

Prime Mover

The prime mover, which may be either an internal-combustion engine or an electric motor, provides power to the pumping unit. The choice of prime mover for a particular well depends on the field conditions and type of power available.

Gear Reducer

The gear reducer is used to convert the high speed and low torque generated by the prime mover into the low speed and high torque required by the pumping unit. The gears are continually lubricated by an oil reservoir contained within the assembly. When in place at the well, the gear train is mounted in an enclosed box.

Pumping unit

The pumping unit changes the rotational motion of the prime mover to a reciprocating vertical motion. The unit is driven by the crankshaft on the gear reducer, and is connected to a polished rod and a sucker rod string, which drives the subsurface pump. Pumping units employ a counterbalance (usually adjustable weights or pressurized air), which opposes the weight of the sucker rod string.

Sucker Rod

The subsurface pump is connected to the pumping unit on the surface by a string of solid sucker rods. These rods are either 25 or 30 foot in length, and have API-standard diameters of 1/2, 5/8, 3/4, 7/8, 1 and 1-1/8 inch.

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Subsurface pumps

The subsurface pump consists of the working barrel, the plunger, the travelling valve and the standing valve. It is actuated by the up and down motion of the sucker rods.

Operation of SRP

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In the downstroke, as the plunger approaches the bottom, the traveling valve is open, and so the standing valve is closed because it is carrying the weight of the fluid above it. At this point in the cycle, the fluid above the standing valve is moving upward through the open traveling valve. During the upstroke, the plunger has reached the bottom of the stroke and is just beginning to move upward. The plunger starts to lift the weight of the fluid above it, and the traveling valve closes. As the plunger continues to move upward, the volume in the working barrel—between the standing valve and traveling valve—increases, while the pressure in the working barrel decreases. As soon as this pressure becomes less than the flowing bottomhole pressure, the standing valve opens and formation fluids flow upward. During each upward movement of the plunger, wellbore fluids are lifted a distance equal to one full stroke length. When the plunger reaches the top of its stroke, its movement is reversed—the traveling valve opens, the standing valve closes and the cycle repeats its reciprocating movement of the rods and the opening and closing of the two valves. With each stroke, fluid is moved up the tubing toward the surface.

Design of Sucker Rod Pump

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Available Data:

1. Allowed Solids: 500mg/l2. Fluid Density: 10 API3. Viscosity of Fluid: 1000cp4. Depth: 500ft5. Lift rate: 400bpd6. Bottom Hole Assembly: 3.5”7. Temperature: 100oC8. Allowed Sand Size: 0.01”-0.001”

Parameters Needed to Design SRP

1. Stroke Length2. Pumping Strokes per Minute3. Polished Road Load (Minimum and Maximum)4. Counter Weights5. Torque

Calculation of Stroke Length

From Design Data given API for Sucker Rod Pumps

Assuming volumetric efficiency as 0.8, the pump displacement is 400bpd. For depth 5000ft and pump displacement 400bpd, from the Sucker rod Pumping unit selection Chart the stroke length is 82 in.

From design data table, for size 320API size and stroke 84inch (as 82 stroke is not available choose 84 strokes)

Conventional Pumping Unit API Geometry Dimensions

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Length of sucker rod in feet=4995, Tubing size in inches=2.5, Plunger size, inches=1.75, Sucker rod size, inches=1, Sp.wt of steel, lb/ft3=490

API geometry dimensions for sucker rod pump (from designation C-320D-213-86) are as follows(as 84 stroke is not available choose 86 stroke)

A=111, C=96.05, I=96, P=114, H=180, G=63, R1=37, R2=32, Cs=450, T=41.61.

Stroke Length ›››

Substituting the values from the above data obtained from the charts we get

S = 85.518 inches

Pumping Strokes per Minute

Putting the values in the equation above, we get N= 30.07 radian/minute

Calculation of Polished Rod Loads

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D = Length of the Sucker Rod, 4995 ft

Tubing Size = 2.5 inches

Ap = Plunger Cross Sectional Area (inch2), Size of Plunger is 1.75 inches

Ar = Sucker Rod Cross Sectional Area (inch2), Size of Sucker Rod is 1 inch

= Density of Steel, 490 lb/ft3

Sf = Liquid Density

Substituting the values

(PRL)max = 38503.396 lb

(PRL)min = 10352.177 lb

Calculation of Counter Weights

This gives Counter Weight as 24427 lb

Calculation of Torque

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This gives the torque needed to be equal to 733802.267 lb-inches

Advantages of Sucker Rod Pumps

1) They can reduce bottom hole pressures to very low levels

2) Offer great flexibility for low to medium productions

3) Simple with respect to design, operation and maintenance

4) Surface and downhole equipment can easily be refurbished, and tends to have high salvage values

5) Most widely known and well-understood systems in the field

6) High lift capacity compared to PCP and ESP

7) Suitable for all kinds of wells as against PCP which is suitable only for oil wells

8) High efficiency of about 80-90%

9) They are suitable for high temperature reservoirs, where ESP experiences seal damage

10) Have a displacement capacity up to 500 bpd, compared to high capacities of ESP and PCP.

11) Lower power consumption for unit production.

12) Optimization controls are available

13) In case of sand producing wells, with slight modification to the bottom hole assembly SRPs can be effectively used

Latest advancements in SRP

Recent and advanced applications of the beam pumping system are successful for overcoming severe industry problems like,

1) Producing high volume wells

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2) Production of high/oil wells

3) Handling high sand content fluids

4) Accurate monitoring and control of the well

5) Producing from highly deviated and horizontal wells

Optimization controllers for rod pumping

With the advent of automation in the oilfield, rod pump control has become an industry standard. While the rod pump controller (RPC) has advanced in reliability and accuracy, the basic principles remain unchanged. Those principles include load and position control, minimizing pump-off and providing data for analysis of the well. Many advances have improved the communication of data, the accuracy of the data collected, and the logic used to provide control. The controller gathers data from the well through load and position sensors and uses the data to calculate downhole pump fillage and optimize production on each stroke. This information is used to minimize fluid pound by stopping or slowing down the pump at the assigned downhole pump fillage setting. By using the unabbreviated application of the wave equation, the well can be controlled with unprecedented accuracy, which enables real-time andhistorical production measurement to be stored in the controller for up to 120 days.

With the recent technology and properly designed SRP systems are highly successful in very high Gas/liquid ratio wells, de‐ liquefying gas wells and the leading system in coal‐bed methane

Pampa style SRP – They have a longer than normal plunger and a shorter than normal barrel. In the upstroke the plunger pulls sand away from the plunger/ barrel interface minimizing the effects of pressure.

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Farr plunger – This increases the pump life and cut well pulling cost drastically.The connector has been moved from the top of the plunger to the bottom of the plunger. This eliminates the gap, wedge and funnel which creates the problems for the conventional plunger. Also, the angle at the top of the plunger has been reversed to force sand inward.

These days even horizontal wells are drilled with SRP. Only wells drilled with short radius tools or wells that have extreme deviation changes due to steering drift are problematic. Programs like S‐ROD with the deviation survey plugged in can predict and design SRP systems for deviated wells.

Coiled rods contain only two connections – one at the top and one at the bottom. They reduce the wear on rod and tubing. They give increased production because of no coupling piston effect, which reduces the friction and increases the plunger over travel. This also decreases the maintenance costs.

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Indian companies involved in SRP manufacturing/ distribution- Aakash oil field services pvt limited- Selan exploration technology limited

References Wikipedia www.norrisrods.com Rod Pumping overview (Google search result) Well-pilot optimization controller for rod pumping Advancements in the area of SRP applications (M Ghareeb, Director: ALS

Lufkin) www.aoscoly.com www.muthpump.com The technology of artificial lift – Kermit E Brown