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 well’s production potential. Denoted by ‘J’

Where Q = total quantity of fluid,Pr = reservoir pressurePwf = Flowing BHPk = permeability, md

srrB

kh

PP

QJ

weoowfr

o

75.0/ln

08.7

)( h = res thickness

re, rw = drainage, well radius, ft

μo = viscosity, cp

Bo = oil FVF

Well’s 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 = PrPwf = Pr

PwfPwf

Pwf = 0Pwf = 0

QQ QmaxQmax

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 Pwf ( Flowing Bottomhole Pressure ).

q

PI = J = -dq / dPPI = J = -dq / dP

Pwf

Inflow PerformanceIPR-When Pr > Bubble Point Pressure :

Combination Constant PI and Vogel Behaviour Case.RATE.

PRESS .

0000

PPwfwf

PPbb

qqqqmaxmax

VOGELBEHAVIOR

CONSTANT J

PPrr

Inflow PerformanceChange Of PI With Cumm. Recovery ( % of Oil In Place ) With Time :

Computer Calculated Inflow Performance Relationships For A Solution Gas Drive Reservoir

PRODUCING RATE , m3/d

BOTTOM-HOLE PRESSURE Kg/cm2

Np/N = 0.1%

2 %

4 %

6 %

8 %

10 %

12 %

14 %

CUMM. REC.,% OF ORIGINAL OIL IN PLACE

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Pwf

Ql

IPR

Tubing Intake Curves

Operating PointOperating Point

QQLL max max

Pr

28


Operating PointsOperating PointsPwf

QlApparent gain

IPR

QQLL max max

Pr

29

Ql

present IPR

Additional gain from stim.


Operating PointOperating Point

QQLL max max

Pr

Pwf

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 PerformanceVOGEL’S WORK ON IPR :

2

max

8.02.01

r

wf

r

wf

P

P

P

P

q

q

SkinThe 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.

ORDimensionless 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

Δps = pressure drop across skinB = formation volume factorμ = viscosity, cps = skin factork = permeability, mdh = height, ftq = flow rate, STB/D

rw

rs

re

KKs

h

w

s

s R

R

K

Ks ln1

skh

qBps

2.141

Skin : Effect on Production

- 0 +

Skin effect

Pro

duct

ion

Flow Efficiency(Wellbore Damage Indicators)

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

Damage Ratio: Inverse of Flow Efficiency

Damage factor = 1- FE =

wfr

swfr

ideal

actual

PP

pPP

J

JFE

swfr

wfr

actual

ideal

pPP

PP

J

J

FE

1

wfr

s

ideal

actual

PP

p

J

J

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 forConstant –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.

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Nodal Analysis………….

Pressure drops at various components

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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 nodeOnly one pressure exists at a node

Nodal Analysis…………..Inflow to the node:

Out flow from the node:

Where Pr = static reservoir pressure

ΔP = pressure drop

Psep = seperator pressure

Pnode = node pressure

nodePcomponentsupstreamP )(Pr

nodesep PcomponentsdownstreamPP )(

Nodal Analysis…………..

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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

introduction to well performance and methods

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