Introduction To Well Performance and Methods

Well Performance
Introduction
What is Well Performance?

It is the ability of a
well to produce
desired fluids
Factors Responsible for Well
Performance?
The overall health of a well depends on:
Geological Aspects
Drilling Aspects
Cementing
Log interpretation
Mechanical aspects of casing & tubing
Drive mechanism
Factors Responsible for Well Performance..
Geological Aspects
Dip
Faults
Oil-water contact
Gas-oil contact
Porosity, permeability, fluid saturation, pay
thickness, pressure etc.
Drilling Aspects
Mud loss
Stuck string
High and / or low pressure formations
Drilling fluid weight, composition etc
Cementing
Composition
Bonding properties
Success of cementation job
Cement rise behind casing
Log interpretation
HC bearing formations
Estimation of thickness
Preciseness of perforation
Porosity and water saturation determination
Mechanical aspects of casing & tubing
Collapse (important in tectonic zones)
Corrosion
Leakage (fluid produced)
Damage (repeated milling etc.)
Stuck up (Fishing etc.)

Drive mechanisms
Solution gas drive
Water drive
Gas cap expansion drive
Compaction drive
Combination drive
Reservoir properties
Porosity
Fluid saturation
Permeability
Absolute
Relative
Mobility & mobility ratio
Solution gas oil ratio

Methods of
Well Performance
IOGPT
Productivity Index
Productivity index is the ratio of flow rate to draw
down. It is indicative of wells production
potential. Denoted by J

Where
Q = total quantity of fluid,
Pr = reservoir pressure
Pwf = Flowing BHP
k = permeability, md
( ) | | s r r B
kh
P P
Q
J
w e o o wf r
o
+
=
=
75 . 0 / ln
08 . 7
) (
h = res thickness
re, rw = drainage, well radius, ft
o = viscosity, cp
Bo = oil FVF
Wells Potential Indicator
kh = 0-100 md-ft not a very
good well

kh = 100-1000 md-ft good
well

kh = 1000-5000 md-ft
excellent well
Pwf = Pr
Pwf
Pwf = 0
Q Qmax
Inflow Performance
It is basically a straight line or curve drawn
in the two dimensional plane, where X axis is
q ( Flow Rate ) and Y axis is P
wf
( Flowing
Bottomhole Pressure ).
q
PI = J = -dq / dP
P
wf
Inflow Performance
IPR-When Pr > Bubble Point Pressure :

Combination Constant PI and Vogel Behaviour Case.
RATE.
PRESS .
0
0
Pwf
Pb
q
qmax
VOGEL
BEHAVIOR
CONSTANT J
Pr
Inflow Performance
Change Of PI With Cumm. Recovery ( % of Oil
In Place ) With Time :

Computer Calculated Inflow Performance Relationships For A Solution
Gas Drive Reservoir

PRODUCING RATE , m
3
/d
BOTTOM-HOLE
PRESSURE Kg/cm
2
Np/N = 0.1%
2 %
4 %
6 %
8 %
10 %
12 %
14 %
CUMM. REC.,
% OF
ORIGINAL OIL
IN PLACE
27
P
wf
Q
l
IPR
Tubing Intake Curves
Operating Point
Q
L
max
P
r
28
Operating Points
P
wf
Ql
Apparent gain
IPR
Q
L
max
P
r
29
Q
l
present IPR
Additional gain from stim.
Operating Point
Q
L
max
P
r
P
wf
PI & IPR
PI attempts to represent the inflow performance
relation of a well as a straight line

IPR usually declines at greater draw downs. It
represents PI tests at several production rates in
order to provide a better representation of the true
inflow performance relation of the well

Inflow Performance
VOGELS WORK ON IPR :

2
max
8 . 0 2 . 0 1
(
=
r
wf
r
wf
P
P
P
P
q
q
Skin
The skin represents a pressure drop which most
commonly arises due to formation damage around the
wellbore, caused by drilling mud or cementing or
other factors.
OR
Dimensionless factor
expressing the reduction in
the formation permeability
compared to the original
permeability

Pwf
Pe
Pressure
drop
due to
radial
inflow
Pressure
drop due
to skin
33
Measurement of Skin

p
s
= pressure drop across skin
B = formation volume factor
= viscosity, cp
s = skin factor
k = permeability, md
h = height, ft
q = flow rate, STB/D
r
w

r
s

r
e

K
K
s

h
|
|
.
|
\
|
|
|
.
|
\
|
=
w
s
s
R
R
K
K
s ln 1
s
kh
qB
p
s
2 . 141
= A
Skin : Effect on Production
- 0 +
Skin effect
P
r
o
d
u
c
t
i
o
n

Flow Efficiency
(Wellbore Damage Indicators)

Is defined as the ratio of the wells actual productivity
index to its productivity index if there were no skin

Damage Ratio: Inverse of Flow Efficiency

Damage factor = 1- FE =
wf r
s wf r
ideal
actual
P P
p P P
J
J
FE
A
= =
s wf r
wf r
actual
ideal
p P P
P P
J
J
FE A

= =
1
wf r
s
ideal
actual
P P
p
J
J
A
= 1
IPR modified by Standing

Well Performance Test Methods
Periodic Production Tests

Productivity or Deliverability Tests

Transient Pressure Tests
Well Performance Test
Methods.
Productivity or Deliverability Tests
Productivity Index
Inflow Performance
Flow after Flow
Isochronal
Well Performance Test
Methods.
Transient Pressure tests
Pressure buildup
Pressure draw down
Multiple rate
Injection buildup or fall-off
Multiple well interference
Drill stem tests
41
Well
Performance
Test
Methods..
Example data for
Constant Rate Pressure Buildup Well
Test
Nodal Analysis or Systems Analysis
Approach
To view the total producing system as a group of
components
Each component of a well system contributes
towards the performance of a well.
To get an improved performance each component
is to be analyzed.
The analysis is done by combining the pressure
versus rate behavior of the well components.

43
Nodal Analysis.
Pressure
drops at
various
components
44
Nodal Analysis.

Location
of nodes
in a well
system
Nodal Analysis..

Each node has one inflow and one outflow
Flow rate through the component can be
determined once the system meets these
requirements
Flow into the node equals flow out of the node
Only one pressure exists at a node

Nodal Analysis..

Inflow to the node:

Out flow from the node:

Where Pr = static reservoir pressure
P = pressure drop
Psep = seperator pressure
Pnode = node pressure

node
P components upstream P = A ) ( Pr
node sep
P components downstream P P = A + ) (
Nodal Analysis..
Nodal Analysis..
Nodal Analysis..
Nodal Analysis..
51
Reference Material
Production Operations Vol 1 & 2 by Thomas O Allen and Alan
P Roberts
Fundamentals of Reservoir Engineering by L P Dake
Technology of Artificial Lift Methods by Kernit E Brown
Advances in Well Test Analysis by R C Earlougher
Development in Petroleum Science (Hydrocarbon Exploration
& Production) by Frank Jahn, Mark Cook & Mark Graham
Hydrocarbon Reservoir & Well Performance by T E W Nind
Principles of Oil Well Production by T E W Nind
Fundamentals of Reservoir Engineering by Brian F Towler

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