handout 2 ptt measurements pcb3013

8/13/2019 Handout 2 PTT Measurements PCB3013

1/12

Well Test Analysis

Pressure Transient Test

Measurements

Refs: Jitendra Kikani, Chapter 3, Kamal et al. SPE Monograph 23, 2009

Kuchuk, Onur, Hollaender, Chapter 1, Pressure Transient

Formation and Well Testing, 2010.

PTT Measurements

Interpretation of pressure, temperature, and

flow-rate measurements has significantly

improved over the past 20 years because of

numerical models and computational

methods.

These interpretation techniques require

detection of subtle and minute changes in

measured quantities for diagnostic purposes.

PTT Measurements

Measurements

Surface Mudline Bottomhole

Slickline

(Memory)

E-line

(SRO)

Permanent

Telemetry

InductionAcoustic

Electromagnetic

Fiber-optic

PTT Measurements

Pressure transient testing hardware are divided into

three basic categories according to their conveyance

systems:

Wireline

, , , ,

Permanent

Wireline units are sometimes combined with pipes or

coil tubing.

Formation testing is usually conducted with a wirelineunit, and well testing is usually conducted with pipe,

tubing, coil tubing, and/or permanent systems.


2/12

Well Test Analysis

PTT Measurements

A wide variety of surface-controlled surface and

downhole equipment is available for conducting well

tests.

When assembled into a test string and run into the

,

production tubing and provides a means controlling

the well.

The downhole test string assembly for exploration

well differs from that for a production well. Test string

assemblies and their operational details depend on

the type of well completion (open or cased-hole).

Pressure

Gauges

(Source: Vella et al.

1992, Schlumberger)

Pressure Gauges

Accuracy: is the difference between a

measured value and the true value generated

by a reference standard DWT (dead weight

.

influencing pressure measurements.

Resolution: is the minimum pressure change

that can be detected by the sensor.

Pressure Gauges

Stability: is the ability of sensor to retain its

performance characteristics over a relatively

long period of time. The stability of the tensor

is the mean drift in psi/day (or psi/hr)

temperature.


3/12

Well Test Analysis

Why Accuracy?

It is important for:

Cross well pressure comparision

Gradient surve s fluid contacts

Reserve estimate OGIP from pressure

Why Resolut ion?


Pressure transient test interpretation

Es eciall hi h ermeabilit reservoirs

Large fractures

IPR

Interference testing

Resolution Resolution1 psi Resolution


4/12

Well Test Analysis

Why Stabili ty?


Long term depletion

Com artmentalization

Interference and well to well comparison

High permeability systems

Why Stability?

Temperature Measurements

Modern electronic gauges measure

temperature as part of the measurement

pressure device.

Temperature data collected along with

pressure can e use o prov e qua y

control for the pressure measurements and

important understanding of wellbore-

dominated effects.

The accuracy and resolution are about of thesame magnitude, ranges from 0.02 oC to

0.5oC.

Temperature Measurements

8000 psi

10oC sudden temperature change


5/12

Well Test Analysis

Flow-Rate Measurements

Surface and downhole flow-rate

measurement devices are different design

because they have different footprints and

their measurement objectives are different

. .

For wireline applications, flow-rate

measurements generally are obtained from

spinner-type flow meters.

Level of accuracy in rate measurements is

still poor.


Level of accuracy in rate measurements is still

poor:

Separator measurements now go into the

computer and the sampling frequency has

,

around 5%. Still most of the time only

surface rates are being measured.

The choke-regulated surface flow rate is

estimated or measured. In some cases, it is

measured sporadically in the gathering tank

after separation of gas from the producedfluid.


Surface rate measurements have three main

drawbacks:

The fluid rate seen by the pressure sensor

is quite different from that measured at the

we ea or n e an .

There is considerable wellbore volume

between the pressure sensor and the

surface where the rate is measured.

The pressure and rate measurements donot correspond to the same time span.


New production loging tools have been

developed to handle cases where spinner-

based measurements are useless, especially

in hi hl deviated and horizontal wells.

They are useful tools, but are quite

expensive, and still not measure the rates,

but something else related to them, holdups

and phase speeds.


6/12

Well Test Analysis

Placement of Gauges

The most appropriate location for a gauge is

at the midpoint perforation (MPP) so that the

appropriate reservoir thermal and density

conditions are emulated.

However, this is not always practical, and

gauges are often placed where the profile

nipple is designed into the wellbore.

Sometimes, it is appropriate to place the

gauge below the perforations in the rathole.

Placement of Gauges In high-rate wells, placement below

perforations may be appropriate to avoid rate

dependent fractional effects on the data

obtained when the gauge is placed above the

MPP. FallingLiquid Level

Recorder run depth

MPP

rathole

Depth

Time

Liquid gradient

Buildup

Placement of Gauges

When the gauge is not placed at the MPP,

the following factors can impact the data and

must be considered during data processing

and ualit control:

Frictional effects manifesting as rate-

dependent skin.

Density changes because of fluid level

moving across the gauge during the test.

Placement of Gauges

Mud in rathole, which makes pressure

correction difficult, or mud displacement

during flow periods, which changes

gradients in the middle of the test.

Thermal storage causing distortion of

pressure data.

Some of these effects can render the test

useless or, worse still, can cause reservoir

information to be misinterpreted (e.g., double-

porosity, layered reservoir behaviors).


7/12

Well Test Analysis

Placement of Gauges

A number of other related dynamic wellbore

phenomena can manifest as subtle changes

in pressure data. These may include:

Liquid influx to or efflux from the wellbore

Plugging

Thermal effects,

Condensation,

Leaks

Geotidal or microseismic events

Placement of Gauges

As discussed, todays electronic gauges offer

high precision measurements and

interpretation techniques based on pressure-

derivative methods that enhances or amplify

an chan es hence the risk of data

misinterpretation rise significantly.

This calls for careful data quality control in

terms of design and data cross-checks.

It is always preferable to have down-hole

shut-in to overcome the effects of the above

mentioned phenomena on pressure data.

Placement of Gauges

These effects and their impact can be

mitigated by taking certain precautions, such

as:

It is always preferable to have down-hole

- .

Running multiple gauges at the same

depth in a bundle carrier.

Running gauges at multiple depths.

Collecting casing pressure and tubing headpressure separately.

Placement of GaugesHorizontal Well Test Example form Kuchuk, Onur, Hollaender, 2010


8/12

Well Test Analysis

Datum Correction

Datum correction provides a common basis for

comparision of well and reservoir pressures

across a given field or even a basin.

This correction is necessary when computing

pressures from Horner plots (i.e. material

balance computations).

However, it is not necessary to perform

datum correction for all BHPs that are

measured for use in computing permeability,

skin, and other reservoir properties.

Datum Correction

For average reservoir pressures datum level is

normally chosen as half the oil volume of the reservoir

is above and half below (why?):

This makes the resultant pressure at this datum

level to reflect the volumetric average oil (or gas)

zone pressure.

This is important for material balance and oil (or

gas) in place calculations. (50 to 100 ft changes in

datum level will have small effect on the results of

material balance.)

To make these calculations we need to know oil

(and/or gas) density (or gradients), and as well as the

oil/water/gas contacts or extend of the boundaries.

Datum Correction

Matthews and Russel (SPE Monograph 1, 1967)

Pressure Correction

Pressures are often corrected from

measurement level to the datum level by using

a so-called tubing gradient. This would be the

case in cases water is in the gauge depth.

Make static gradient surveys when lowering or

pulling back the bomb. Also, we need to have

the densities of water and oil.


9/12

Well Test Analysis

Pressure Correction

Matthews and Russel (SPE Monograph 1, 1967)

Generic Gauge Recommendations(Kikani, 2009, SPE M. 23)

Electronic gauges are common today and

should be used because of their superior

precision and resolution.

and/or tabulars are perforated, pressures

above reservoir pressure can be anticipated

for short durations. Select proper gauge

rating to accomadate these conditions.

Always run backup gauges, preferably in a

bundle carrier.


For long term installation, gauge drift

characteristics should be considered in

selecting the gauge.

o

(177oC), run at least four gauges, preferably

using different gauge technologies.

For critical jobs, calibrate gauges before use

(most multiuse gaugesa are calibrated every6-12 months).


Run the gauges as close to perforations as

possible, especially in prolific gas wells.

If condensate is expected to drop out in the

well and form a liquid layer, use a pressure

an a erent a gauge to mon tor t e u

movement and density changes.

Use surface pressure and temperature data

along bottomhole data to resolve ambigous

wellbore effects.

Run static and flowing gradient surveys

before and/or after a test is complete.


10/12

Well Test Analysis

Summary on PT Testing

PT Testing is a well/reservoir description and

evaluation method used to obtain in-situ

dynamic well/near well/reservoir properties.

It is certainly a valuable tool that, like all other

indirect determination methods, should be

used with understanding of the physical and

mathematical concepts and the inherent

nonuniqueness of the model and its

parameters.

Modified from Kamal et al. (SPE Monograph Vol. 23, 2009)


It should be used with a complete

understanding of the geological and

operational aspect of the field.

It is often necessary to run several types of

transient tests and to integrate their results

with other characterization methods to obtain

a valid description of the reservoir.

Modified from Kamal et al. (SPE Monograph Vol. 23, 2009)


Interpretation of all PT tests rely on:

identifying flow regimes,

calculating initial reservoir system

properties from these flow regimes, and

story matc ng t e ent re test t roug t e

use of an appropriate interpretation model,

and nonlinear regression.

Most of the models currently in use are

analytical, but technology is moving toward tothe use of numerical modeling (or numerical

well testing in general).


Derivatives and deconvolution make PTT

interpretation analysis a reliable tool for

well/reservoir characterization.


11/12

Well Test Analysis


BUTs (Source: Kuchuk, Onur, Hollaender, 2010; Pressure TransientFormation and Well Testing)

Selecting a proper test type and

measurement system is one of the most

important step in PT Testing.

Pressure accuracy and resolution have

improved considerably, but the same

cannot be said for flow rate measurements.

A downhole and/or surface data acquisition

system should deliver the data at specified

accuracy, resolution, and drift to achieve

the test objective.


BUTs

Surface and downhole conditions

considerably affect the pressure gauge and

rate measuring device performance.

Therefore, it is important to assess these

conditions when selecting gauges and a

data acquisition system.


BUTs

The reservoir model can also be used to

assess effects of accuracy, resolution, and

drift on the test objective and interpretation.

, ,

we can determine what the minimum

pressure gauge and drift should be to

estimate the fault conductivity and distance

to an active well at a reasonable testingduration from an interference test.


BUTs

Pressure gauge accuracy and resolution of

pressure and rate data affect pressure

derivative and deconvolution considerably.

Once the testing hardware and acquisition

sytem with gauges are selected and placed

downhole, current testing hardware

systems do not allow us to change or

modify them.


12/12

Well Test Analysis


BUTs

Therefore, they have to be evaluated and

selected carefully because it will be very

after setting it in the wellbore.

handout 2 ptt measurements pcb3013

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