the university of texas at austin downhole gas separator performance in sucker rod pumping system...

The University of Texas at Austin

Downhole Gas Separator Performance In Sucker Rod Pumping System

Beam Pumping WorkshopHouston, Texas

October 4 - 7, 2005

Manuel GuzmanAugusto Podio

Overview

Description of the problem

System schematic

Bubble flow forecast

Gas separation testing facilities

Pump volumetric efficiency for actual wells

Conclusions

What Is The Problem?

Design and selection of downhole gas separators are usually made using heuristics.

Generally the performance is much below than expected.

V liquid in V liquid in anchoranchor

V plungerV plunger

V slipV slip

V gas in V gas in anchoranchor

Downhole Separator System

Gas Velocity Inside the Anchor

V V plungerplunger

Net gas velocityNet gas velocity is difference is difference

between between gas slip gas slip velocity (up)velocity (up)

liquid velocity liquid velocity (down)(down)

Liquid velocity

depends on:

• ID of anchor

• OD of dip tube

• Plunger diameter and velocity

Instantaneous Liquid Flow Rate

Conventional

Dplunger=1 in

Ls=86 in

8.45 SPM

200 BPD

Upstroke Downstroke

Forecast for Different Bubble Sizes

Clift, Grace and Webber (1978)

Stroke 1 Stroke 2 Stroke 3

Bubble motion inside a separator with rod pump.Diam. Dip tube=1.5 in Plung. Diam.=1.5 in

Conventional Unit, Ls=86.3 in, 8.45 SPM. Flow rate=151 BPD

Gas Separator Testing – Univ. of Texas

BHP

Air purge Hyd

rost

atic

Co

lum

n

Flow Controlto keep BHPconstant

Air Supply

Air out

Manifold

Mix Pump

L.C.

50 ft high/ 6 in. diam.

Gas Separator Testing – Univ. of Texas

PerforationsSeparator Inlet Slots

Dip Tube Separator Tube

Casing

Liquid rate of the pump

the well (BPD)

Gas rate entering

the well (MSCF/D)

Gas

Rate

thro

ugh

Separa

tor

(MSC

F/D

)

1

2

3

45

6

78

SEPARATOR TYPE: Echometer 1 (2 x 4" slots)

Air and water entering below ports @ 10 psi

2

5

8

Separator Performance (Continuous Flow)

Downhole gas separator selection

With several options of separators it is difficult to select the right one.

Two common situations: I have a well with specific conditions, which

separator is my best choice? I have a separator, In which kind of well can I

use it efficiently?

Separator Selector Spreadsheet

Designed for using with Excel©

Determine separator performance for continuous flow

Input: Average liquid rate Gas rate Casing diameter

Output: Separator that offers the greatest liquid fillage

for the given conditions

Example

200 BPD and 100MSCFD with a 7” casing Patterson 1 using a 3 1/2” separator would offer

the best performance

Inputs (liq. rate, gas rate, csg. diam.)

Region of zero gas thru pump

Gas is entering the pump

Boundary obtained with lab data

Outputs (separator, dimensions)

Superficial Liquid Velocity

inside Separator (in/sec)

Superficial Gas Velocity

in casing annulus (in/sec)

Gas

Rate

th

rou

gh

S

ep

ara

tor

(MS

CF/

day)

1

6

5

2

3

4

PATTERSON 1(OD DIP TUBE = 1”; # OF SLOTS =8; DIMEN. OF THE SLOTS =8" x 1/8")

Pc = 10 psi; POSITION OF THE SEP. = ABOVE THE PERFORATIONS

What If This Were a Rod Pumped Well?

Superficial Liquid

Velocity varies during

the stroke

Sucker Rod Simulator

A special butterfly valve was built and installed in the return line It will be automatically operated to obtain the desired on/off time Flow will be measured using a mass flow meter after the valve

Pipe

½ in shaft2

in

Motor

z

x

6 in

Driv

e

Intermittent Flow Behavior

Gas enters the pump only during a fraction of the 5 sec. upstroke.

Gas column moves uniformly during each stroke.

Bubble size distribution changes with during stroke.

Patterson 8Flow rate = 275 BPD

Gas rate = 55 MSCFDPump speed =6 SPM (1 stroke = 10 sec)

Calculated Pump Liquid Fraction (Fluid Entering Below Ports)

A reduction in pump liquid fraction was found when dip tube diameter was increased (Echometer 2 & Patterson 5)

Up to 87% of liquid fillage can be achieved None of the evaluated separators reached the goal of 100%

Conventional Unit, fluid entering below anchor portsDplunger=1.5, Ls=90, SPM=8.37, PIP=10psi 151 BPD

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Echometer 1 Echometer 2 Patterson 3 Patterson 5 Poorboy

Pum

p fill

per

centa

ge

(%)

.

50

35

20

Vg (in/s)

Conclusions

The instantaneous flow rate during the pump stroke should be used for the separator design.

The gas flow rate in the casing has a major effect on the gas separation efficiency.

Separator efficiency depends on the stroke length (Ls), plunger speed and the dip tube diameter, for each given geometry in a rod pump well.

Visual observation confirms that the best way to maximize the gas separation is to set the intake below the perforations, if possible.

Future work: carry out additional intermittent flow tests to validate the mathematical predictions.

Special thanks to: Yates Petroleum

Q&A Session

The University of Texas at Austin

Downhole Gas Separator Performance In Sucker Rod Pumping System

Beam Pumping WorkshopHouston, Texas

October 4 - 7, 2005

Effect of Geometry

Liquid rate entering

the well (BPD)

Gas rate entering

the well (MSCF/D)

Gas

Rate

th

rou

gh

S

ep

ara

tor

(M

SC

F/d

ay)

Liquid rate entering

the well (BPD)

Gas rate entering

the well (in/sec)

Gas

Rate

th

rou

gh

S

ep

ara

tor

(MS

CF/

day)

Poorboy Patterson 3

Number of holes: 12 Diameter: 3/8” Area 1.3 in2

Number of slots: 8Dimension: 8" x 1/2“Area 32 in2

Background Research

Understanding and Combating Gas Interference in Pumping Wells. Joe Clegg, 1963

Another Look at Gas Anchors. Joe Clegg, 1989

Characterization of Static Downhole Gas Separators. Jorge Robles, 1996

The Effect of Geometry on the Efficiency of Downhole Gas Separator. Omar Lisigurski, 2004

Mark II (3”OD, 1” Dip Tube)

Rotaflex (3”OD, 1” Dip Tube)

Liquid Fraction (Mark II, fluid entering below the anchor ports)