Phase Redistribution Effect On Pressure Trensient Analysis.pptx

PHASE REDISTRIBUTION EFFECT OF PRESSURE TRANSSIENT ANALYSIS GUIDED BY MS.S.VIJAYALAKSHMI Asst. Prof,

Dept. of Petroleum Engineering, Rajiv Gandhi College Of Engineering.

PRESENTED BY

JAGAN.T (211915219029), KARTHICK.R (211915219036), PRASANTH.K (211915219056), SRI SOORIYAN.A (211915219075), B.TECH,

1

Petroleum Engineering, Rajiv Gandhi College Of Engineering, APRIL-2019.

27-Mar-19

INTRODUCTION  Wellbore phase redistribution (WPR) occurs in wells where more

than one phase flow.  WPR may cause in the wellbore storage coefficient in both drawn

downs and buildups.  WPR may dominate a well test for several hours.  Gravity, Friction and Acceleration effects play an important role in

this scenario.  Initial research has focused on empirical models to identify and

match WPR.  75% of wells showed the effect of WPR. 2

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Fig.1: Log-log derivative plots, increasing wellbore storage due to phase redistribution in the wellbore.  Typical derivative shapes due to WPR where reported in Fig.1 where 3

curve 5 is typical of situations where the denser phase re-enter into the formation. 27-Mar-19

PRESSURE TRANSIENT ANALYSIS 

The first PTA method was introduced in the 1950’s with specialized plot. і. Semi-log ii. MDH (Managed Data Holding) iii. Horner

 It is initially called as well test interpretation.  Generally on a shut-in period after a stable production phase during

which the production rate was measured.  It is initially focused on a specific flow regime called Infinite Acting

Radial Flow (IARF). 4

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 Specialized plots for other flow regimes were developed are

i. Liner ii. Bi-liner iii. Pseudo-steady state.

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Fig.2: Flow regimes.

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METHODOLOGY  The development of analytical models in 1980/1990’s.  Processor hungry models in 1990/2000’s.  The name drifted from well test interpretation to the more

generic term Pressure Transient Analysis.  It was about making diagnostic, to take decisions,

including remedial action on well. 6

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FIG.3: Methodology. 7

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PRESSURE BUILDUP TEST  This test is conducted by,

і. Producing a well at constant rate for some time, ii. Shutting the well in, iii. Allowing the pressure to buildup in the well bore, and iv. Recording the pressure in the wellbore as a function of time.  It

is frequently permeability.

possible

to

estimate

formation

 This test is based largerly on a plotting procedure

suggested by horner. 8

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 This test can be further classified into,

i. Ideal buildup test ii. Qualitative behavior of field test iii. Modification for multiphase flow

I.IDEAL BUILDUP TEST  A test in an infinite, homogeneous, isotropic reservoir

containing a slightly compressible, single-phase fluid with constant fluid properties.

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 Flow into the wellbore ceases totally.

 The above equation suggests that shut-in BHP, recording during a pressure

buildup test.

FIG.4: Rate history for ideal pressure buildup test  In the Fig.4 Well has produced a time tp at rate q before shut-in and if well

call time elapsed since shut-in ∆t.

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II.QUALITATIVE BEHAVIOUR OF FIELD TEST  To develop the background required to understand this test.  It provides a convenient means of introducing some factors.  ETR, MTR, and LTR.

 The Horner plot is usually impossible unless the MTR can be

recognized. 11

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Fg.5: Actual buildup test graph.

Fig.6: Characteristic influence of afteflow on horner graph

 In Fig.5 based on this concept we logically can divided a

build up curve into three regions.  The characteristic influence of afterflow on a pressure

buildup test plot is a lazy S-shape at early time in Fig.6. 12

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III.MODIFICATION FOR MULTIPHASE FLOW  The drawdown equation becomes,

 The buildup equation becomes,

 For infinite acting reservoir.  Phase remain essentially uniform throughout the drainage area

of the tested well. 13

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FIG.7: Behavior of the static pressure on shut-in oil well.  In Fig.7 the reason for distortion of the straight line in the ETR and

LTR are as follow: In the ETR and LTR the curve is affected by, i. Altered permeability near the wellbore,

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ii. Wellbore storage.

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ANALYSIS OF WELL TEST USING TYPE CURVES  The quantitative use of type curves in well test

analysis.  SPE well test monograph.  Specific type curves discussed include

i. Ramey type curves ii. Mckinley’s type curves iii. Gringarten type curves 15

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FUNDAMENTALS OF TYPE CURVES  To

determine formation permeability characterize damage and stimulation.

 Simulating

and

to

constant-rate pressure drawdown test,

buildup test.  They may allow test interpretation even when wellbore

storage distorts most.  Convectional methods fails. 16

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 Some of these solutions are analytical.  The reservoir be at uniform pressure before the drawdown test.  Boundary conditions,

i. Infinitely large outer drainage radius. ii. Constant surface withdrawal rate combined with wellbore storage.  Skin factor “S”, this causes an additional pressure drop, which

is proportional to instantaneous sandface flow rate. 17

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I.RAMEY’S TYPE CURVE  Constant rate pressure drawdown test in a reservoir with

compressible, single phase liquid flowing.  Production, Constant withdrawal rate at surface, wellbore

storage and concentrated wellbore damage.  No assurance that use of these curves can lead to a valid

test interpretation.

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Where, CS - wellbore storage constant, ∆t - time elapsed, ∆p – pressure change.

FIG.8: Use of type curve to determine end of wellbore storage distortion. 19

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 In Fig.8 wellbore storage has ceased distorting the pressure

transient test data when the type curve for the value of CSD=0.

II. GRINGARTEN TYPE CURVE  Hydraulically fractured wells in which vertical fractures

with two equal length wings.  Uniform flux into the fracture.

 High fracture conductivity.

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 This study was made for finite reservoir.  A constant rate drawdown test for a slightly compressible

liquid, also can be used for buildup test and gas wells.

FIG.9: Gringarten type curve for vertically fractured well centered in closed square, no wellbore storage, uniform flux

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 Although not apparent on a log-log plot, a semi-log plot of

the data in Fig.9 is a straight line signifying radial flow when for xe/Lf >5, tDLf =2.  In linear flow,

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WELLBORE STORAGE  After a rate change, part of the production may be due to

expansion or compression of fluid in the wellbore.  Due to a moving fluid contact.

I.DRAWDOWN  The assumption of a constant rate.  Surface flow rate “q” is constant. 23

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 The first production comes from the wellbore and not the

reservoir.

 Reservoir flow rate “qsf”.

 The fluid produced is q, the sum of fluid from the

wellbore is qsf, fluid coming from the reservoir is qsf. 24

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FIG.10: Surface and sandface production are not equal initially

 The first production comes from the well. This illustrate is

below.

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FIG.11: Surface and sandface production as a function of time

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II.ONE PHASE IN WELLBORE  Semi-log analysis is possible when qwb≈ 0. Then the wellbore

storage effect has died out. The production from the wellbore is given by,

 where

is the compressibility and is the volume of the compressed fluid. The pressure drawdown, ∆, is given by,

 For negligible sandface production, i.e. qsf≈0 , all the fluid

produced at the surface derives from fluid expansion.  Since the surface rate, q, is constant, the above differential

equation may be integrated to yield, 26

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 The above equation describes a straight line with slope

m=qB/Cs , and intersect pi with C, the vertical axis.

Fig.12: Well flowing pressure as a function of time

 The wellbore constant is given by,

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III.PRODUCTION BY A MOVING FLUID INTERFACE  The below well has been close.  The pressure at the top may fall below the bubble point.

 In this case there is no packer.

FIG.13: Oil production by a falling gas liquid interface 28

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 When production is started, the gas liquid contact will move

downwards. Again the production from the wellbore is given by,

 Where the wellbore storage constant is,

 Since qwb = q, the above differential equation may be integrated

to yield,

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FIG.14: volume of compressed fluid, downhole shut-in

 Downhole shut-in reduce the volume of fluid dramatically in

the above fig.

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CONCLUSION  The methodology was developed for the study of

wellbore phase redistribution.  WPR was found in two-phase flow test before the end

of wellbore storage.  Air flow rate was found to have a higher effect than

water flow rate on WPR.  The phase re-injection was successfully simulated. 31

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 The lower the reservoir pressure, the higher the liquid

re-injection, reservoir.

an

analogue

to

low

permeability

 For a closed system, WPR was shown to take place.

 A porous medium should be used to simulate the near

wellbore region between the reservoir and the well. 32

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