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Rock porosity

2013-03-18

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Porosity: The ratio of the pore volume of a rock to the total volume of a rock. Reflects the ability of the formation to store fluids.

Effective porosity: The volume of pores in which fluid can flow freely and the percentage of rock volume.

Primary porosity: The ratio of primary pore volume to formation volume.

Secondary porosity: The ratio of secondary pore volume to formation volume.

Thermal neutron lifetime: refers to the average time that a thermal neutron passes through from the moment of generation to the moment of being captured.

Radionuclide: An unstable nuclides that spontaneously alter structure, decay into other nuclides and emit radiation.

Formation density: the volume density of rock, which is the mass per cubic centimeter of rock.

Formation pressure: formation pore fluid

(

Oil, gas, water

)

pressure. Also known as formation pore pressure. Formations with formation pressures above normal are called abnormally high pressure formations. Formations with formation pressures below normal are called abnormally low pressure formations.

Cement bond index: the ratio of the sound amplitude attenuation rate of the target well section to the sound amplitude attenuation rate of the fully cemented well section.

Zhou Bo jump: A phenomenon in which the amplitude of "sudden big and small" changes sharply on the acoustic time difference curve.

An interface: the cemented surface between the casing and the cement.

Second interface: the cemented surface between the formation and the cement.

Sound wave time difference: the reciprocal of sound speed.

Resistivity: A physical quantity that describes the strength of a medium's electrical conductivity.

Oil and gas saturation (including hydrocarbon saturation)

Sh

): The relative volume of pores occupied by oil and gas in the pores.

Water saturation

Sw

: The relative volume of water in the pores. The sum of oil and gas saturation and water saturation is

1.

The concept of saturation in logging:

1.

Hydrocarbon saturation of undisturbed formations

Sh

=

1

-

Sw

.

2.

Flushing zone residual hydrocarbon saturation:

Shr

=

1

-

Sxo

(

Sxo

Indicates the water saturation of the rinse zone).

3.

Movable oil (hydrocarbon) saturation

Smo

=

Sxo

-

Sw

or

Smo

=

Sh

-

Shr

.

4.

Tethered water saturation

Swi

With residual water saturation

Swr

In direct proportion.

Mud content: Percentage of muddy volume and formation volume.

Salinity: The concentration of salt in a solution. The ratio of the weight of the solute to the weight of the solution.

SP

Curve characteristics:

1.

Mudstone Baseline: A natural potential curve corresponding to a homogeneous, thick mudstone formation.

2.

Maximum static natural potential

SSP

: The natural potential reading of a homogeneous, completely water-containing pure sand layer is inferior to the mudstone baseline reading.

3.

scale:

SP

The linear scale marked on the graph's head is used to calculate the natural potential difference between the non-mudstone and the mudstone baseline.

4.

Anomaly: refers to the permeability of the stratum than the baseline of the mudstone.

SP

Curve position. (

1

Negative anomaly: in a sandstone rock profile well, when the well is a dry cement slurry

(Cw>Cmf)

Permeable formation

SP

The curve is located to the left of the mudstone baseline (

Rmf>Rw

)

;

(

2

Positive anomaly: in the sandstone rock profile well, when the well is a salt cement slurry (

Cmf>Cw

), permeable stratum

SP

The curve is located to the right of the mudstone baseline (

Rmf

).

5.

The shape of the curve: (

1

The curve is symmetric about the midpoint of the formation;

(2)

Thick formation

h>4d

The amplitude of the natural potential curve is approximately equal to the static natural potential, and the half-depth of the curve is directly opposite the interface of the formation. (

3

The reading of the thinning curve with the formation is affected by the surrounding rock, the amplitude becomes lower, and the half-point moves toward the surrounding rock.

SP

Application of the curve:

1.

Dividing the permeable rock stratum: a negative anomalous perm permeable rock layer in the pale cement slurry, which is abnormally surrounding the permeable rock stratum in the salt cement slurry. After the permeation layer is identified, the position of the permeation layer interface is determined by the half-width method.

2.

Estimate the shale content formula.

3.

Determine the formation water resistivity.

4.

Judging the water-flooded layer: When the injecting water is different from the original layer water and the drilling fluid, the baseline of the mudstone layer adjacent to the water-flooded layer is offset, and the offset is related to the degree of flooding.

Apparent resistivity curve characteristics: (

1

Gradient electrode system theoretical curve: asymmetry curve. Dividing the top gradient curve (inverted trapezoid) and the bottom gradient curve (positive trapezoid), a straight line segment appears in the middle of the formation. As the formation becomes thinner, the straight line segment does not exist, and the high-resistance thin layer has only a maximum value, at the bottom of the high-resistance layer. A false maximum occurs at the depth of the electrode.

(

2

The theoretical curve of the potential electrode system: the symmetry curve. Take the extreme value of the midpoint of the formation.

Factors affecting the apparent resistivity curve:

1.

The influence of the electrode system;

2.

The impact of the well;

3.

Surrounding rock - the effect of thick layers;

4.

Intrusion impact;

5.

Shielding effect of high-resistance adjacent layer;

6.

The influence of the dip angle of the formation.

Apparent resistivity curve application:

1.

The lithology profile is divided according to different lithological resistivity;

2.

Find the true resistivity of the rock formation;

3.

The rock layer porosity, formation water resistivity and oil saturation are applied, and the Archie formula is applied.

4.

Seeking oil layer

Ro

value;

5.

Comparing the measurement curves of different electrode systems can determine the intrusive characteristics of the formation and, if conditions permit, the pore fluid properties can be determined.

Deep and shallow double lateral curve characteristics (

Rlld, Rlls

):

1.

The two curves of the permeable layer do not coincide;

2.

In the permeable layer, when the deep resistivity is greater than the shallow resistivity, the mud is low intrusion, and conversely, high intrusion;

3.Rmf>Rw

At the time, the low intrusion is often the oil and gas layer, and the high intrusion is the water layer.

4.

The two curves of the non-permeable layer coincide;

5.

When the non-permeable layer is shallow and double lateral, the stratum resolving power is the same, that is, the longitudinal conductivity of the stratum changes uniformly.

Dual lateral logging applications:

1.

Determining the true resistivity of the formation;

2.

Divide the lithology profile;

3.

Quick and intuitive judgment of the oil-water layer: the difference between the depth and the shallow side of the well in the permeable layer, the depth is greater than the shallow positive difference, which means that the mud is low-invasion, which is the oil-bearing well section; when the depth is less than shallow, it is called the negative amplitude difference, which is the water-bearing well. segment.

Microelectrode system logging curve (micro gradient, micro potential) application:

1.

Dividing the line of words and lines: the micro-potential and the micro-gradient do not coincide with the permeation layer. The coincidence and low resistivity are non-permeability layers. When the micro-potential is larger than the micro-gradient, it is a positive amplitude difference. When the micro-potential is smaller than the micro-gradient, it is a negative amplitude difference.

2.

Determining the rock formation interface;

3.

Determining the effective thickness of the oil-bearing sandstone;

4.

Determining the well diameter to expand the well section;

5.

Determine the irrigating band resistivity

Rxo

And mud cake thickness

Hmc.

Summary of the steps to divide the oil and water layer:

1.

The permeation layer and the non-permeation layer are divided by a microelectrode system curve (coincidence is a non-permeation layer, non-coincidence is a permeation layer, usually the micropotential is greater than a micro-gradient);

2.

by

SP

Curve look

Rmf, Rw

Relationship, if it is negative, then

Mf>Rw

If it is abnormal, then

Rmf

;

3.

Judging the oil and water layer by the depth and lateral resistivity curve,

Rmf>Rw

When, if

Rlld>Rlls

, the mud is low intrusion, it is known that the permeable layer is the oil and gas layer, if

Rlld

The mud is highly invaded, and it is known that the permeation layer is an aqueous layer. on the contrary,

Rmf

At the time, contrary to the above conclusion.

Application of sonic time difference logging curve:

1.

Judging the gas layer: (

1

) generating a cycle jump (

2

The acoustic time difference increases;

2.

Divide the stratum,

3.

Determining rock porosity formula

Sonic Amplitude Logging Application:
(

1

Cement cementing logging (

CBL

Mainly when measuring the signal energy (casing wave) to determine the quality of an interface bond, the better the interface bonding, the lower the casing wave amplitude, the worse the interface cementing, the higher the casing wave amplitude.
(

2

Acoustic variable density logging (

VDL

):

1

Where the free casing (no cement outside the casing) and the first and second interfaces are not cemented, the casing wave is strong and the formation wave is weak or completely absent;

2

There is a good cement ring, and the first and second interfaces are well cemented, the casing wave is weak, and the formation wave is strong;

3

When the cement and the casing are cemented well and the formation is not well cemented (that is, the first interface is well cemented and the second interface is not well cemented), both the casing wave and the formation wave are weak.

Characteristics of natural gamma logging curves:

1.

When the radioactivity content of the upper and lower surrounding rocks is the same, the curve is symmetric about the stratum;

2.

The highly radioactive formation has a maximum value against the center curve of the formation and increases as the thickness of the formation increases. When the thickness is more than three times the diameter of the well, the maximum value is constant, which is only proportional to the natural radioactivity of the rock, and the thickness of the formation determined by the half-width of the curve is the true thickness. It is difficult to divide when the diameter is less than three times.

Application of natural gamma curves:

1.

Divide lithology;

2.

Stratigraphic comparison, using gamma logging curves for stratigraphic comparison has the following advantages:

910

It has nothing to do with the salinity of formation water and mud. (

2

Under normal conditions, it is independent of the nature of the fluid (oil or water) contained in the formation. (

3

) It is easy to find the standard layer on the curve.

3.

Estimating the shale content formula;

4.

School depth: the sounding will be error-based, but the curve shape is similar;

5.

Midway logging: There is a section in the middle that will repeat, and the gamma curve will become a complete data band, that is, adjusted by gamma curve.

Application of density logging:

1.

Determining the porosity of the formation is the primary application of density logging.

2.

Identifying the gas layer, judging the lithology, and overlapping the density logging and the neutron logging curve can identify the gas layer and judge the lithology.

3.

The density-neutron log intersection map method determines the lithology for porosity.

Compensation for neutron logging applications:

1.

Determine formation porosity.

2.CNL

versus

FDC

Logging meets for porosity and determines lithology.

3.

Density and compensation neutron overlap determine lithology.

4. CNL

versus

FDC

The limestone porosity curve overlaps qualitatively to determine the gas layer.

Neutron gamma logging curve application:

1.

Dividing the gas layer: The neutron gamma log at the gas layer shows a high count rate value.

2.

Determine the oil-water interface: the neutron gamma log count rate in the water layer is greater than the neutron gamma log count rate in the reservoir, but the neutron gamma can only be used if the formation water salinity is high. The logging curve divides the oil-water interface and distinguishes the oil-water layer.

Carbon and oxygen ratio spectrum logging factors (

C/O

):

1.

Oil-bearing porosity of the formation: When the lithology is constant, the oil-bearing porosity is high, and the carbon-oxygen ratio is high.

2.

Stratigraphic lithology: If the formation minerals contain carbon nuclei, the carbon and oxygen ratio of such formations is greater under the same porosity.

C/O

Application of the curve:

1.

Determine oil saturation

So

.

2.

Dividing a flooded layer: flooded

C/O

The curve value is significantly lower than that of the unflooded part

C/O

value.

Classification of reservoirs: According to lithology, it is divided into clastic reservoirs, carbonate reservoirs and special lithologic reservoirs.

Separation of the permeable layer in the sandstone section:

1.

Natural potential curve: the permeation layer shows a negative or positive anomaly relative to the mudstone baseline.

GR

The low value is the permeation layer and the high value is the non-permeability layer.

2.

Microelectrode curve: the difference between the osmotic layer micropotential and the microgradient oil, and the micropotential is greater than the microgradient. The non-permeability layer micropotentials and microgradients have no or only a small amplitude difference.

3.

Well diameter curve: The permeable layer is relatively straight, but the diameter of unbonded sandstone or conglomerate may also expand.

Find the gas layer:

1.

The acoustic time difference-neutron gamma curve overlaps the gas finding layer: the two curves of the water layer coincide, the acoustic wave time difference is large, and the neutron gamma logging value is high.

2.

The compensation neutron logging-density logging curve overlaps: the two curves do not coincide but the staggered amplitude difference is the gas layer, and the difference between the two curves is small.

Mud: A medium that flows through a well while drilling.

Mud filtrate: Mud entering the pores of the wellbore formation under a certain pressure difference.

Formation water: Water within the pores of the formation.

The degree of salinity of the solution: the concentration of the salt in the solution. The ratio of the weight of the solute to the weight of the solution.

Ion diffusion: When two different concentrations of salt solution are contacted, the ions in the high concentration solution migrate through the permeable membrane to the low concentration solution under the action of osmotic pressure.

Rock skeleton: The fraction of solid particles that make up the sedimentary rock.

Mud intrusion: The mud column pressure is usually kept slightly greater than the formation pressure during the drilling process. Under the pressure difference, the mud filtrate invades into the permeable layer, and the mud filtrate replaces the original fluid contained in the permeable layer to form an intrusion zone, and the shale particles in the mud adhere to the well wall to form a mud cake. Call mud intrusion. Divided into two types: intrusion band resistivity

Ri

Less than the original formation resistivity

Rt

Called low intrusion, and vice versa. Low intrusion is the basic feature of the oil layer, and high intrusion is the basic feature of the water layer.

Describe several parameters of rock elasticity: Young's modulus

E

, Poisson's ratio, shear modulus, volume deformation elastic modulus

K

, Lame constant.

Nuclide: refers to a similar atom in the nucleus with a certain number of protons and neutrons and in the same energy state. The number of protons and the number of neutrons in the nucleus of the same nucleus are equal. There are two types of nuclides that are stable and unstable.

Half-life: from

t=0

Time

No

An atomic nucleus begins, to

No/2

The time it takes for a nucleus to decay, used to illustrate the rate of decay,

T

Said.

The role of gamma rays and matter:

1.

Photoelectric effect:

r

The ray passes through the substance and collides with the electrons in the atom, and transfers its energy to the electron, causing the electron to move away from the atom and move.

r

The photons themselves are absorbed entirely, and the electrons that are released are called photoelectrons. This process is called photoelectric effect.

2.

Compton effect: When the energy of a gamma ray is medium,

r

When a ray collides with the outer electrons of an atom, a part of the energy is transmitted to the electron, and the electron is emitted from a certain direction. This electron is called Compton electron, and the ray that loses part of the energy is scattered in the other direction. Gamma ray, this phenomenon is called the Compton effect.

3.

Electron pair effect: when incident

r

The energy of the photon is greater than

1.022MeV

When it interacts with matter, it will make

r

Photons are converted into pairs of electrons, a negative electron and a positron, which are themselves absorbed.

The depth of detection of the electrode system: centering on the power supply electrode, making a spherical surface with a certain radius, if the medium included in the spherical surface contributes to the measurement result

50

At %, this radius is defined as the depth of detection of the electrode system.

The natural radionuclides in rocks are mainly: the types and contents of radioactive elements contained in different rocks are different, which are related to the lithology and the physical and chemical conditions in the formation process.

GR

The larger the value, the stronger the radioactivity.

Application of radioisotope logging: find the location of the gutter; check the sealing effect; check the fracturing effect; determine the water absorption profile and calculate the relative water absorption.

The role of neutrons and matter: fast neutron inelastic scattering; fast neutron activation of the nucleus; elastic neutron scattering and thermal neutron capture.