00-Why Well Test
Transcript of 00-Why Well Test
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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.
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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
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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
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Oil Production Test History
From
To
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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
??
?
?
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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.?
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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.
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First Oil Well evaluations
The well value was given by its production :
The production test did not exist.
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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
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1920's: Purely Empirical
Objective was purely economic, not technical.
From: Estimation of
Underground Oil
Reserves by Oil-Well
Production Curves
Cutler (1924).
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The Evolution of the Well Test Analysis
From 1924
To 2004
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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.
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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:
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History plot (Pressure [psia], Liquid Rate [STB/D] vs Time [hr])
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Beginning in Well Test Analysis
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
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Beginning in Well Test Analysis
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.
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Well Test Analysis in the 1950s
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4500
4700
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MDH plot: p [psi] vs log(dt)
kh, skin
1950 : Miller Dyes Hutchinson: permeability and skin
determination from drawdown transient behaviour
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1951. Horner permeability and damage determination from
a build-up analysis
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Horner plot: p [psi] vs log(tp+dt)-log(dt)
kh, skin
Extrapolated
pressure
Well Test Analysis in the 1950s
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0 2 44450
4650
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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:
Well Test Analysis in the 1950s
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Well Test Diagnosis Evolution
1960s : first type curves (Ramey, McKinley, Argawal etc) to
diagnose the flow regime.
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Well Test Diagnosis Evolution
Or for specific models: i.e. McKinley
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Well Test Diagnosis Evolution
The conventional methods dominated until the late 70s and the
type curve matching remained a confidential method, made by
hand :
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Well Test Diagnosis Evolution
1970s : new type curve presentation and introduction
of their use in Oil fields. (A.C.Gringarten D. Bourdet et al)
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Well Test Diagnosis Evolution
1982 : Introduction of the derivative type curve (D.Bourdet)
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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]
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Well Test Analysis Latest Development
1990s - : Computer Modelling/ Matching/ Forecasting
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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.
....
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Well Test Analysis: Present - Future
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Well Test Analysis: Future
End of Analytical?
Numerical Only...