11 well testing facile doc.pdf

8/10/2019 11 well testing facile doc.pdf

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Well TestingTechniques

UTC

Module PKR09

WELCOME

RAJNESH GOGOI


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UTC

Module PKR09

Well testing is the technique and method

for the evaluation of well conditions and reservoir

characteristics.

It involves producing a well at a constant rate or

series of rates, some of which may be zero (well

closed in), while simultaneously taking a continuous

recording of the changing pressure in the well boreusing some form of pressure recording device.

WHAT IS WELL TEST


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UTC

Module PKR09

To determine the following parameters

Initial pressure (p)

Average pressure within the drainage boundary (p)Permeability thickness product(kh) and

permeability(k)

Mechanical skin factor (S)

Area drained (A)Dietz shape factor (CA)

WHY TEST A WELL


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Types of Well Tests

Productivity Well Test

Descriptive/Reservoir Test


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Productivity Well Tests

Well is produced at several flow

rates

Stabilized BHP is measured

Plot of Pwf Vs Q = IPR

Slope of lines indicative of well

productivity

Pwf

Q


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Applications of Productivity Well Tests

Identify produced fluids

Measure reservoir pressure and temperature

Obtain samples for PVT analysis

Evaluate completion efficiency

Evaluate workover or stimulation treatments


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Descriptive/Reservoir Testing

Involves introducing abrupt changes in production

Associated changes in BHP monitored

Disturbances penetrate more than near-wellbore

Other reservoir properties can be determined

Shape of Pw Vs time curve is defined by reservoircharacteristics


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Applications of Descriptive Tests

Evaluate Reservoir parameters

Skin,Flow Efficiency,Productivity index

Permeability

Reservoir pressure

Characterize reservoir heterogeneity

Reservoir extent/geometry

Hydraulic communication


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Well Testing In Different Phases

Drilling phase

Open hole testing(Descriptive )

DST

RFT

Completion Phase

Productivity Tests

Production phase Cased hole testing

Descriptive Tests


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Important datas required in well testing

Core,log data(to check homogeneity,dual porosity,OWC,GWC etc.)

RFT,pressure depth profiles(to check pressure equilibrium and thus

homogeneity)

Geological model(for structural interpretation,position of OWC,GOC)

Drive mechanism

PVT fluid properties(Pb,Bo,Co,

Well completion(partial completion and partial penetration)

Tests in neighbouring wells completed in the same reservoir

Equipment (position of pressure gauge from reservoir datum depth)


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Types of Well Tests

Pressure Drawdown

Pressure Build up

Multirate Injection/fall-off

Interference

Pulse


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Pressure Drawdown Tests

Shut in the well till

pressure reaches

static level & then

flowing the well at aconstant rate ,q &

measuring Pwf.

Pwf

t

qShut in

time

rate


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BASIC EQUATION OF PRESSURE DRAWDOWN TEST:

Pwf=Pi(162.6qBo/kh)((log t + log (k/Ctrw2)3.23+0.87s)

This is the equation of a straight line with slopem = 162.6(q Bo/kh)

From slope permeability and skin can be calculated as

k = 162.6(q Bo/mh)and

skin,S = 1.151(((P1hr - Pwf)/m) - log(k/ Ctrw2 )+3.23)


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Advantages:

Suitable in new wells

No need to lose production

K,S,reservoir size can be determined

Disadvantages:

Difficult to maintain constant production rate.

Long shut in so that Pi is achieved is required.So suitable in new

wells.


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Mulitrate Tests

Accounts for variable rate

history

Applications

Rate variations

kh product, Pr

Boundary

configurations

Skin,FE,PI etc.

Pwf

q1q2

qn-1qn

Pi

0 t1 t2 tn-1 tn

Time,hrs


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Mulitrate Tests

Advantages: No problem with variable flow rate

No loss of production

Reduced wellbore storage Disadvantages:

Rate fluctuations are difficult to

measure,especially on a continuous basis.

Q1Q2

Q3


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Pressure Build-up Tests

Most preferred well testing

technique

The well is first produced at a

constant rate till pressure is

stabilized and then the well is

shut in

Pressure is recorded as a

function of time

Pwf

ttp

flowingShut-in

q

Pi


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The basic equation of pressure build up test is Pws= Pi - (162.6qBo/kh)log(tp+t/t) (Horner equation)

This is the equation of a straight line when plotted as Pw Vs

log (tp+t/t) (Horner plot) with slope m

=162.6qBo/kh and intercept P

i From this k & s can be determined as k =

162.6(qBo/mh) and S =

1.1513(((P1hr-Pwf)/m)-log( k/ Ctrw2 )+3.23) Fault

distance=(0.0122ktx/ Ct)1/2 pskin= 0.87ms


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Advantages:

Precise control of rate

P* can be determined

Disadvantages:

Loss of production due to shut in.Q(t)


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Well Test Planning Before designing a test an engineer should ensure that there should

not be

more than one zone open to wellbore

interzone communication due to poor cement bond

partial zone completion

It includes

Test type

Test duration


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Well Test Planning

Operational requirements well completion data

location and pattern of wells completed in the same

reservoir

rate data

fluid type

pressure data


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Well Testing - Data Acquisition

Downhole Recorders Record pressure and temperature

Components

Pressure Gauge

Power Source Memory unit

1 to 2 recorders used

Surface pressure readout

Wireline link


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Well Test Data Analysis

Diffusivity Equation

Model Recognition

Interpretation Software


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DARCYS LAW AND ITS APPLICATION

IN 1856, A FRENCH ENGINEER HENRY DARCY

FORMULATED THE LAW

THIS IS THE MOTHER OF ALL RESRVOIR ENGINEERING

CALCULATIONS

STUDY WAS ON UNCONSOLIDATED SAND FILTER BEDS


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DARCYS LAW STATES THAT THE VELOCITY OF A

HOMOGENEOUS FLUID IN A POROUS MEDIA ISPROPORTIONAL TO THE PRESSURE GRADIENT, AND

INVERSELY PROPORTIONAL TO THE FLUID VISCOSITY

V= - (K/ ) ( P/ L)=q/A


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APPLIES ONLY IN LAMINAR FLOW

DOESNOT APPLY IN TURBULENT FLOW

DOES NOT REPRESENT THE FLOW THROUGH

INDIVIDUAL PORE SPACES BUT AVERAGES THE

FLOW OF SEVERAL PORE CHANNELS.IT IS ASTATISTICAL LAW


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THE UNIT OF PERMEABILITY IS DARCY.

A ROCK OF 1DARCY PERMEABILITY IS ONE IN

WHICH A FLUID OF 1 CP VISCOSITY MOVE AT A

VELOCITY OF 1CM/SEC UNDER A PRESSURE

GRADIENT OF 1ATMOSPHERE/CM.


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THE UNIT OF PERMEABILITY IS DARCY.

A ROCK OF 1DARCY PERMEABILITY IS ONE IN

WHICH A FLUID OF 1 CP VISCOSITY MOVE AT A

VELOCITY OF 1CM/SEC UNDER A PRESSURE

GRADIENT OF 1ATMOSPHERE/CM.


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APPLICATIONS

TO CALCULATE THE FLOW RATE

TO CALCULATE THE P.I. OF A WELL

TO CALCULATE PRESSURE DRAWDOWN

IN RESERVOIR SIMULATION

TO INCREASE PRODUCTIVITY BY WELL

STIMULATION


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A properly designed, executed, and analyzed well test can provide information:

about formation permeability

reservoir initial or average pressure

sand-face condition (well damage or stimulation)

volume of drainage area

boundary and discontinuities

reservoir heterogeneity

distance or extension of the fracture induced

validation of geological model.

To sum up : Well Test


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Well Test data when combined with hydrocarbon production data, and laboratory

data on fluid and rock properties:

afford the means to estimate the original hydrocarbon in-place

and the recovery that may be expected from the reservoir under various modes of

exploitation

In addition, well test data and IPR well performance equations, combined with

production data, help to design, analyze, and optimize total well production systemor production optimization.

To sum up : Well Test

Further, it is important to determine the ability of a formation to produce

reservoir fluids and underlying reason for a well's productivity.


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FlareSurge Tank

3 Phase

seperatorChoke

manifold

I/Heater

Lab cum data

center

Pumps

Typical layout of well test setup


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48 THREE PHASE SEPARATOR


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CHOKE MANIFOLD


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3 HEAD SEA SNAKE BURNER


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GROUND FLARE


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Assumptions:

Horizontal flow of a single phase fluid inward to a wellbore

located at the center of a radial volumetric element

Formation is both homogeneous and isotropic

The central well is perforated across the entire formationthickness

Negligible gravity effect

Applicability of Darcys law

,,Ct ,k are independent of pressure

Single phase fluid is present in the reservoir


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2p/ r2+ 1/r ( p/ r) = (Ct k) p/ t

Partial differential equation

Describes physical processes occurring in the reservoir

Solutions depend on boundary conditions

Reservoir ExtentInitial Pressure


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MDH plots

Q(t)

Pws

log (t)

LTRMTRETR

Deep fracture,small wbs

Small wbs

No s,no wbs

+s,large wbs

- s,large wbs

No s medium wbs

+s,small wbs

Closed boundary

Semi log straight line

Constant pressure boundary

Pressure increase due to fault

Pressure decline from offset production


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LOG-LOG PLOTS

Log-log plots are used in welltest interpretation

It is a plot of pressure change Vs log( tp+t/t) in BU & Vs logt in DD

In wellbore storage affected region it gives

unit slope line

Derivatives are differentiation of pressurechange wrt time

Boundary effects are evident by late time

variation of the derivative value Q(t)

Pressure

change &

derivative

Elapsed time


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LOG-LOG PLOTS

0.010 0.100 1.000 10.000 100.000

01x10

11x10

21x10

31x10

41x10

Elapsed t ime

Pres

surec

hange

&

deriva

tive

1.5 log cycles

1

6

4

3

2

5

7

1=Infinite homogeneous reservoir

2=No flow barrier-faulted reservoir3=Parallel faults-linear reservoir

4=Perpendicular faults

5=Constant pressure boundary

6=Parallel no flow &constant

pressure boundary

7=Net pay variation-linear


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Special Cases In Well Testing Afterflow

occurs because of surface shut in

end of this region can be approximately 1 1/2log cycle

away from unit slope


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LOG-LOG PLOTS

0.010 0.100 1.000 10.000 100.000

01x10

11x10

21x10

31x10

41x10

Elapsed t ime

Pre

ssurec

hange

&

deriva

tive

1.5 log cycles


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Special Cases In Well Testing Partial penetration or completion

results in additional pressure drop

S=(ht/hp)sd+sp where s=total skin ht=total

formation thickness hp=perforated

interval sd=damage skin sp=partial penetrationskin

sp=(ht/hp-1)(ln(ht/hp(kh/kv)0.5)-2)


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Some Special Formation Types Composite System

the fluid & rock properties varies in a steplike fashion

in radial direction away from the well

. well

Zone 1: k1,ct1, 1, ,1

Zone 2:k2,ct2, 2 ,2


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Some Special Formation Types Layered Reservoir:Two types

layered reservoir with crossflow in which the layers

are hydrodynamically communicating at the contact

planes

layered reservoir without crossflow in which the layerscommunicate only through wellbore(commingled

production)


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Some Special Formation Types Double porosity system

two distinct porosity types-matrix & fracture porosity

the condition applies to fractured reservoir or layered

reservoir with a large contrast in rock properties


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HORNER PLOTS(Double porosity system)

0.010 0.100 1.000 10.000 100.000

01x10

11x10

21x10

31x10

41x10

Elaps tyed t ime

Dim

ens

ion

lessp

ressure

1.5 log cycles

Pw

Elapsed time


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Pressure Transient Analysis

Raw Data

Model

Identification

log-log analysis

Specialized

Analysis

Well and Reservoir

Parameters

Checking Procedures

Methodology


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Pressure Transient Analysis - Steps

1. Draw diagnostic (log-log) plot

2. Identify flow regimes

3. Draw specialized plots(if any)

4. Calculate well and reservoir parameters 5. Choose basic well and reservoir model and

re-compute parameters using Type Curves

6. Check for consistency by comparing results


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Model Recognition


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Step 5: Re-compute parameters using Type Curves

Type Curves

Generalized solutions to diffusivity equation

Graphical form

Depends on reservoir models and flow regimes Most common

Homogeneous reservoir with wellbore storage

Type Curve Matching

Diagnostic Plot is matched with a Type Curve Calculate parameters from given equations


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Type Curve for a Homogeneous Reservoir

Wellbore Storage Effect

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