Testing 3

Front 1

late time transient data

Back 1

The portion of the pressure transient occurring after radial flow. Analysis provides characterization of outer boundaries such as faults or fluid contacts.

Front 2

layer

Back 2

A slab of reservoir rock bounded above and below by another layer in vertical hydraulic communication.

Front 3

layered reservoir testing

Back 3

An advanced testing technique using a combination of transient-rate and pressure measurements and stabilized flow profiles to determine permeability and skin for each of several layers commingled in a well.

Front 4

limited entry

Back 4

A completion with only a portion of the productive interval open to flow, either by design or as a result of damage. Results in partial penetration.

Front 5

line source solution

Back 5

The solution to differential equations treating the well as a vertical line through a porous medium.

Front 6

linear flow

Back 6

A flow regime characterized by parallel flow lines in the reservoir. This results from flow to a fracture or a long horizontal well, or from flow in an elongated reservoir, such as a fluvial channel, or as a formation bounded by parallel faults. It is recognized as a +1/2 slope in the pressure derivative on the log-log diagnostic plot. Its presence enables determination of the fracture half-length or the channel or reservoir width, if permeability can be determined independently.

Front 7

liquid level

Back 7

The depth at which the first liquid is found in a well.

Front 8

material balance

Back 8

An expression for conservation of mass governed by the observation that the amount of mass leaving a control volume is equal to the amount of mass entering the volume minus the amount of mass accumulated in the volume.

Front 9

middle time transient data

Back 9

A common term for the infinite-acting radial flow regime. This portion of the pressure-transient response is between wellbore-dominated flow regimes in the early-time transient data and boundary-dominated flow regimes in the late-time transient data.

Front 10

modified isochronal test

Back 10

A type of deliverability test conducted in gas wells to generate a stabilized gas deliverability curve (IPR).

Front 11

modified isochronal test

Back 11

A multirate test designed as a series of drawdown and buildup sequences at different drawdown flow rates, with each drawdown and buildup of the same duration. The purpose of the test is to determine well deliverability, and this type of test is most commonly done in gas wells.

Front 12

multiphase flow

Back 12

The simultaneous flow of more than one fluid phase through a porous medium.

Front 13

False - well test analysis generally assumes single phase flow

Back 13

True or false - most well test analysis assumes multiphase flow?

Front 14

multiple rate tests

Back 14

Tests conducted at a series of different flow rates for the purpose of determining well deliverability, typically in gas wells where non-Darcy flow near the well results in a rate-dependent skin effect.

Front 15

naturally flowing well

Back 15

A well in which the formation pressure is sufficient to produce oil at a commercial rate without requiring a pump.

Front 16

non-Darcy flow

Back 16

Fluid flow that deviates from Darcy's law, which assumes laminar flow in the formation. Typically observed in high-rate gas wells when the flow converging to the wellbore reaches flow velocities exceeding the Reynolds number for laminar or Darcy flow, and results in turbulent flow. Since most of the turbulent flow takes place near the wellbore in producing formations, the effect of this flow is a rate-dependent skin effect.

Front 17

nonideal gas

Back 17

A gas described by an equation of state of the form pV = znRT, where z is the gas deviation factor dependent on pressure, temperature and gas composition.

Front 18

oil formation volume factor

Back 18

Oil and dissolved gas volume at reservoir conditions divided by oil volume at standard conditions.

Front 19

oil well

Back 19

A producing well with oil as its primary commercial product.

Front 20

partial completion

Back 20

Completion of or flow from less than the entire producing interval. This situation causes a near-well flow constriction that results in a positive skin effect in a well-test analysis.

Front 21

partial penetration

Back 21

An incompletely drilled portion of the productive interval.

Front 22

Henry Darcy

Back 22

Who showed that the common mathematics of heat transfer could be modified to adequately describe fluid flow in porous media?

Front 23

permeability thickness

Back 23

This product is the primary finding of buildup and drawdown tests and is a key factor in the flow potential of a well.

Front 24

phase redistribution

Back 24

A pressure phenomenon caused in a wellbore by rise of gas and fall of liquids trapped in a wellbore after a surface shut-in. This phenomenon can cause a "hump" in the buildup curve, and frequently leads to incorrect analysis of buildup test results because the entire early portion of the transient is adversely affected by this pressure response.

Front 25

pore-pressure gradient

Back 25

A change in pore pressure as a function of distance. This can refer to radial change in pore pressure with distance from the well (which can be calculated from well-test analysis results) or to change in pore pressure with depth

Front 26

porous medium

Back 26

A rock or soil with interconnected pores that permit flow of fluids through the medium.

Front 27

pressure

Back 27

The force distributed over a surface, usually measured in pounds force per square inch, or lbf/ in.2, or psi, in US oilfield units.

Front 28

pressure buildup

Back 28

A rise in well pressure as a function of time observed after a well is shut in or after the production rate is reduced.

Front 29

pressure depletion

Back 29

The drop in average reservoir pressure from fluid production.

Front 30

pressure drawdown

Back 30

The differential pressure that drives fluids from the reservoir into the wellbore.

Front 31

pressure falloff

Back 31

The pressure decline after halting or reducing fluid injection in a well.

Front 32

pressure gauge

Back 32

A device used to measure pressure.

Front 33

pressure gradient

Back 33

A change in pressure as a function of distance. This can refer to radial change in pore pressure with distance from the well (which can be calculated from well-test analysis results), to change in pore pressure with depth (which can be measured by formation tests, and implies formation fluid density and/or fluid contacts) or to change in wellbore fluid pressure with depth (which can be measured with production logs, and implies wellbore fluid density).

Front 34

pressure squared plot

Back 34

A plot of p2 versus time function used to analyze low-pressure gas-well drawdown and buildup tests. The square term arises from substituting a gas-law equation into the differential equations where required to account for fluid compressibility. This allows an approximation for the differential equations that approaches the linear form required to use the classical solutions of the diffusion equation.

Front 35

pressure transient analysis

Back 35

The analysis of pressure changes over time, especially those associated with small variations in the volume of fluid.

Front 36

pressure transient well tests

Back 36

Well tests in which pressure is recorded as a function of time and interpreted using various analysis methods.

Front 37

pressure-drawdown analysis

Back 37

The analysis of pressure-transient behavior observed while the well is flowing. Results are generally much less accurate than those from pressure buildup tests

Front 38

production period

Back 38

The flow period before a buildup. The duration of the production period should be specified in the test design to assure that a stable flow situation is reached

Front 39

prorated well

Back 39

A well in which the maximum production rate is fixed by law. These laws were developed by producing states primarily to control the market and avoid periodic price collapses.

Front 40

pseudopressure plot

Back 40

A plot of real gas pseudopressure (pseudopotential) m(p) versus time function used to analyze gas-well drawdown and buildup tests. The use of the real gas pseudopressure linearizes the diffusion equation for gas flow. This form enables rigorous analysis over all pressure ranges. The pressure-squared plot can be used for low pressure (p < ~2000 psi), and pressure can be used to analyze gas-well tests at high pressure (p > ~3000 psi).

Front 41

pseudosteady state

Back 41

Behavior observed when a well reaches stabilized production from a limited drainage volume. For constant-rate production, under pseudosteady state, the difference between the flowing wellbore pressure and the average reservoir pressure in the drainage volume is constant, and the pressure drawdown is a linear function of time, resulting in a unit slope in the log-log pressure derivative. The late-time buildup pressure will level off to the average reservoir pressure if the buildup duration is sufficient long, resulting in a sudden drop in the log-log pressure derivative. Pressure depletion occurs

Front 42

pumping well

Back 42

A well produced by use of some kind of downhole pump.

Front 43

pumping well tests

Back 43

Testing that is accomplished by measuring pressure in the annulus, or by pulling the pump and running a pressure gauge in the hole.

Front 44

radius of investigation

Back 44

The calculated maximum radius in a formation in which pressure has been affected during the flow period of a transient well test. his may also be termed transient drainage radius.

Front 45

single phase flow

Back 45

The flow of a single-phase fluid, such as oil, water or gas, through porous media.

Front 46

skin

Back 46

A dimensionless factor calculated to determine the production efficiency of a well by comparing actual conditions with theoretical or ideal conditions.

Front 47

skin

Back 47

The zone of reduced or enhanced permeability around a wellbore, often explained by formation damage and mud-filtrate invasion during drilling or perforating, or by well stimulation.

Front 48

skin effect

Back 48

An increase or decrease in the pressure drop predicted with Darcy's law using the value of permeability thickness, kh, determined from a buildup or drawdown test. The difference is assumed to be caused by the "skin." Skin effect can be either positive or negative. The skin effect is termed positive if there is an increase in pressure drop, and negative when there is a decrease, as compared with the predicted Darcy pressure drop. A positive skin effect indicates extra flow resistance near the wellbore, and a negative skin effect indicates flow enhancement near the wellbore.

Front 49

skin factor

Back 49

A numerical value used to analytically model the difference from the pressure drop predicted by Darcy's law due to skin.

Front 50

spherical flow

Back 50

A flow regime that occurs when the predominant flow pattern in the reservoir is toward a point. This flow occurs for partial penetration and limited-entry completions. This flow regime is recognized as a -1/2 slope in the pressure derivative on the log-log diagnostic plot. Its presence enables determination of the spherical permeability. When spherical flow is followed by radial flow, both horizontal and vertical permeability can be quantified.