Types and Purposes of Well Tests

Pressure transient tests

We generate and measure pressure changes with time

Deliverability tests

Well controlled production

(Production Analysis)

Use of production data for goals usually achieved by well

testing

Goals of pressure transient tests (PTA)

to quantify important reservoir rock, and fluid properties permeability, porosity and average reservoir

pressure

to locate and identify reservoir heterogeneities sealing faults, natural fractures, and layers

to characterize near wellbore and wellbore conditions affected by drilling and completion operations

Production data analysis

:Reservoir properties (permeability, skin

factor, fracture half-length, etc).

Reservoir pore volume (estimated using

long-term production performance).

Estimated ultimate recovery (EUR)—

movable fluid volumes.

PTA: Single-Well Tests

one well in which the pressure response is measured following a rate change.

pressure buildup test shut in after controlled production

drawdown or flow test (specific drawdown tests: are called reservoir limits tests)

pressure falloff test similar to a pressure buildup test, except it is, conducted

on an injection well injectivity test

Inject into the well at measured rate and measure pressure as it increases with time

analogous to pressure drawdown testing.

PTA: Multiwell Tests

Flow rate is changed in one well

Pressure response is measured in one or more

other wells

Directional variations of reservoir properties

(orientation of natural fractures)

Presence or lack of communication between two

points in the reservoir

Ratio of the porosity-compressibility products of

the matrix and fracture systems

Multiwell tests:

Interference tests The active well is produced at a measured, constant rate

throughout the test(Other wells in the field must be shut in so that any

observed pressure response can be attributed to the active well only.)

Pulse testsThe active well produces and then, is shut in, returned to

production and shut in againRepeated but with production or shut-in periods rarely

exceeding more than a few hoursProduces a pressure response in the observation wells

which usually can be interpreted unambiguously (even when other wells in the field continue to produce)

Deliverability tests (DT)

production capabilities of a well under specific reservoir conditions

primarily for gas wells

absolute openflow (AOF) potential

inflow performance relationship (IPR) or gas backpressure curve

DT: Flow-After-Flow Tests

(referred to as gas backpressure or four-point tests)

producing the well at a series of different stabilized

flow rates

measuring the stabilized bottomhole flowing pressure

at the sandface

typically, with a sequence of increasing flow rates

DT: Single-Point Tests

low-permeability formations

flowing the well at a single rate until the

bottomhole flowing pressure is stabilized

required by many regulatory agencies

requires prior knowledge of the well's deliverability

behavior

(from previous testing or from correlations with other wells

producing in the same field under similar conditions)

DT: Isochronal Tests

Specifically, the isochronal test is a series of single-

point tests developed to estimate stabilized

deliverability characteristics without actually flowing

the well for the time required to achieve stabilized

conditions

The isochronal test is conducted by alternately

producing the well, then shutting in the well and

allowing it to build up to the average reservoir pressure

prior to the beginning of the next production period.

General Test Design Considerations

If properly designed and implemented, a well test

can provide much useful information about both

individual wells and the reservoir

In general, the goals of a well test are not only to

obtain sufficient. data to meet the stated

objectives, but also to accomplish these tasks in

a timely and inexpensive manner

Issues

Development Wells vs. Exploration Wells Producing Wells vs. Injection Wells Shallow Wells vs. Deep Wells Stimulated Wells vs. Unstimulated Wells Effects of Reservoir Properties Low Permeability vs. High Permeability Formations Single Zones vs. Multiple Zones Safety and Environmental Considerations Sweet Gas vs. Sour and Corrosive Gases Other environmental Concerns 

Production data analysis

:Reservoir properties (permeability, skin

factor, fracture half-length, etc).

Reservoir pore volume (estimated using

long-term production performance).

Estimated ultimate recovery (EUR)—

movable fluid volumes.