00-Why Well Test

8/10/2019 00-Why Well Test

1/16

1987-2005 -050118

1

Well Testing A Definition

A well test is a period of time during whichthe rate and/or pressure of a well is

recorded in order to estimate well or

reservoir properties, to prove reservoir

productivity, or to obtain general dynamic

reservoir data.

1987-2005 -050118

2

Objectives of Well Testing

A well test might be performed for one or more of the following reasons:

Identification of the in-situ reservoir fluids

Evaluation of near-wellbore reservoir properties

Determination of well productivity

Collection of representative reservoir fluid samples

Identification and characterization of faults and boundaries

Determination of reservoir limits


2/16

1987-2005 -050118

3

Conducting Well Tests

Most well tests consist of changing the rate, and

observing the change in pressure caused by thischange in rate. To do this, there are four basic

requirements for a pressure transient test:

1. We need to be able to measure time

2. We need to be able to measure rate

3. We need to be able to measure pressure

4. We need to be able to control rate

1987-2005 -050118

4

Oil Production Test History

From

To


3/16

1987-2005 -050118

5

First Oil Discoveries

Just after the discovery of the

existence of hydrocarbon

reservoirs, the oil prospectors and

producers did not know more

about oil than the first gold miners

about gold

??

?

?

1987-2005 -050118

6

First Oil Discoveries

A well was drilled in a location by

instinct and was produced to the max.

Without knowing why, from where and

how the oil was flowing.?


4/16

1987-2005 -050118

7

First Oil Production

The objective was to maintain the highest production

rate as long as possible.

It was known that the production was linked to the

well head pressure.

The influence of other nearby producing wells was

neglected .

The evaluation of the connected volume (reserves?)

was not a major concern.

1987-2005 -050118

8

First Oil Well evaluations

The well value was given by its production :

The production test did not exist.


5/16

1987-2005 -050118

9

Well Test History

State-of-the-Art in the 1920s:

Empirical approaches based on production and pressure declineextrapolations were developed:

The relationship between pressure and rate

Well Productivity Index and rate potential from the Well Head

Pressure

The first Bottom Hole Pressure data are measured

1987-2005 -050118

10

1920's: Purely Empirical

Objective was purely economic, not technical.

From: Estimation of

Underground Oil

Reserves by Oil-Well

Production Curves

Cutler (1924).


6/16


7/16

1987-2005 -050118

13

The Evolution of the Well Test Analysis

From 1924

To 2004

1987-2005 -050118

14

Beginning of Well Test Analysis

1929: Pierce and Rawlins first relation between rate and BHP

1930s

1936 Rawlins and Shellhardt: AOFP

1935 Theis: mathematical model

1937 Muskat : Use of BHP extrapolation

The relationship between the pressure and the production

rate became imperative.

Test designs were developed to address this problem: the

multi-rate tests.


8/16

1987-2005 -050118

15

Beginning in Well Test Analysis

The well test objective was still to establish the relation of the stabilized

production rate and its corresponding flowing pressure:

-5000

0

26/04/1910 28/04/1910 30/04/1910 02/05/1910 04/05/1910 06/05/1910

0

25005000

History plot (Pressure [psia], Liquid Rate [STB/D] vs Time [hr])

1987-2005 -050118

16


There was no drive to establish a relation between the production

rate and the formation properties.

These properties were measured experimentally and were not yetthe objectives of a test.

The test designs are limited to measure stationary behaviour:

Steady State or Pseudo Steady State


9/16

1987-2005 -050118

17


In the 1940s, efforts are made to understand and determine

the parameters governing the fluid flow in the reservoirformation.

The Darcys law and diffusivity equation are the base of this

search (1856!).

These dynamic parameters could be accessed during the

transient pressure behaviour.

1987-2005 -050118

18

Well Test Analysis in the 1950s

-2 0 2

4500

4700

4900

MDH plot: p [psi] vs log(dt)

kh, skin

1950 : Miller Dyes Hutchinson: permeability and skin

determination from drawdown transient behaviour


10/16

1987-2005 -050118

19

1951. Horner permeability and damage determination from

a build-up analysis

0 2 44450

4650

4850

Horner plot: p [psi] vs log(tp+dt)-log(dt)

kh, skin

Extrapolated

pressure


1987-2005 -050118

20

0 2 44450

4650

4850

Horner plot: p [psi] vs log(tp+dt)-log(dt)

Infinite Acting Radial Flow

Still, the Horner and MDH methods assumed a certain type of flow

regime for the equation to be valid:



11/16


12/16

1987-2005 -050118

23

Well Test Diagnosis Evolution

1960s : first type curves (Ramey, McKinley, Argawal etc) to

diagnose the flow regime.

1987-2005 -050118

24


Or for specific models: i.e. McKinley


13/16

1987-2005 -050118

25


The conventional methods dominated until the late 70s and the

type curve matching remained a confidential method, made by

hand :

1987-2005 -050118

26


1970s : new type curve presentation and introduction

of their use in Oil fields. (A.C.Gringarten D. Bourdet et al)


14/16

1987-2005 -050118

27


1982 : Introduction of the derivative type curve (D.Bourdet)

1987-2005 -050118

28

Well Test Analysis Computerization

The introduction of the derivative allowed the computerization of

the modern WT analysis methods:

Log-Log plot: dp and dp' [psi] vs dt [hr]


15/16

1987-2005 -050118

29

Well Test Analysis Latest Development

1990s - : Computer Modelling/ Matching/ Forecasting

1987-2005 -050118

30

Well Test Analysis: Present - Future

The increasing computing power of PCs and recent developments in

numerical methods, re-vitalised old tools: numerical modelling.

This allows us to use real physics:

make a grid on-the-fly include changing reservoir thickness and porosity

create reservoir models respecting the real geometry

regress on the parameters (numerically)

include pressure dependant permeability

use real gas flow equations (especially in tight reservoirs)

use material balance in depleting gas reservoirs

multi-phase with proper rel perms.

....


16/16

1987-2005 -050118

31

Well Test Analysis: Present - Future

1987-2005 -050118

32

Well Test Analysis: Future

End of Analytical?

Numerical Only...

Documents

00-Why Well Test