Introduction to Well Testing

Introduction to Well TestingInstructional Objectives

1. List 4 objectives of well testing.

2. Define testing variables.

3. Compute compressibility of reservoir systems.

Introduction To Well TestingOutline

• Applications and objectives of well testing

• Development of the diffusivity equation

• Definitions and sources for data used in well testing

What Is A Well Test?• A tool for reservoir evaluation and

characterization– Investigates a much larger volume of the

reservoir than cores or logs– Provides estimate of permeability under in-

situ conditions– Provides estimates of near-wellbore condition– Provides estimates of distances to

boundaries

How Is A Well Test Conducted?qq = 0

t

q

t

p

Well Test Applications

• Exploration

• Reservoir engineering

• Production engineering

Well Test Objectives

• Define reservoir limits

• Estimate average drainage area pressure

• Characterize reservoir

• Diagnose productivity problems

• Evaluate stimulation treatment effectiveness

Types of Well Tests

q

Single-Well Multi-Well

Development of the Diffusivity Equation

The Diffusivity Equation

• Describes the flow of

– A slightly compressible fluid

– Having constant viscosity

– In a porous medium

– At constant temperature

The Continuity Equation

21 vAvAm

(Av)1 (Av)2

Equation of State for a Slightly Compressible Liquid

oppcoe

Flow Equation - Darcy’s Law

or, in differential form,

LpkA

q

xpk

u xx

The Diffusivity Equation

tp

kc

rp

rrr

1 t

Data Used in Well Testing

Formation Volume Factor

surf

reso V

VB

Viscosity

dy v

v + dv

dydv

A

F

Fluid Compressibility

pVln

pV

V1

c oo

oo

Porosity

Permeability

pALq

k

Pore Compressibility

p

ln

p

1cf

Net Pay Thickness

h = h1 + h2 + h3

Shale

Sand

h3

h2

h1

Net Pay Thickness

Case 1 Case 3

Case 4Case 2

SaturationsH2O

Wellbore Radius

rw

Total Compressibility

ggwwooft cScScScc

Exercise 1

• List 4 objectives of well testing

Exercise 2

• Define variables used in well testing

Exercise 3

• Calculate total compressibility for an undersaturated oil reservoir

Exercise 4

• Calculate total compressibility for a saturated oil reservoir

Exercise 5

• Calculate total compressibility for a low-pressure, high-permeability gas reservoir

Exercise 6

• Calculate total compressibility for a high-pressure, low-permeability gas reservoir