Elementos de geofísica de poço

7/30/2019 Elementos de geofsica de poo

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Elements of geophysical well

Formation Evaluation


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Definition and types of profiles

Profile is any discrete or continuous registration in scale of physical, chemicand biological agents over a pit. According to the parameters or registered fo

the purpose of registries, the profiles are given different names.


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PROFILE DETERMINAO (USO NA AVALIAO)

1. RESISTIVITY Sality, Fluid

2. ACUSTIC Velocity. Porosity. Lithology

3. RADIATIVITY Shaliness, Porosity, lithology

4. ELETROMAGNETIC Lithology. Porosity. Fluid

5. DEPTH Depping layers

6. CALIPER Well Diameter.

7. TEMPERATURE Gradient & Temperature

8. TELEVISION Frastures. Well Form.

Lithology

9. VERTICAL SEISMIC Velocity, seismograms

10. NUCLEAR MAGNETIC Lithology, Fluids, texture

11. DENSITY Porosity, Correlation

12. NEUTRONIC Porosity


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Methods More Used

Eletrical Resistivity (ES) Eletormagnetc Indution

spontaneous Potential (SP)

Nature Radioativity or induced (GR) Sonic Velocity

Temperature


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Properties Obtained

Thickness Formations Lithology

Porosity

Permeability Water saturation and/or hydrocarbons

Depping Layers, and

temperature


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Application For the thickness of the layers in general uses:

Resistivity spontaneous Potential

Radioactivity

Sonic Velocity

The estimates of porosity, are based on measurements : Resistivity, sonic velocity and radioactivity

In addition estimates of porosity can be obtained by profiling gamma radensity, neutron logging, gamma ray logging and resonance.


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Resistivity

What is it?

It is the ability of a substance has to stop the flow of an electriccurrent through it, each material has a resistivity :

Rm = resistivity mud;

Rmc= resistivity of the screed;

Rxo= resistivity of the washed zone;

Rmf= resistivity of the mud filtrate;

Rt = resistivity true of the formation (Virgin Zone);

Rw = Water's formation resistivity;

Ra = apparent resistivity;

Ro = resistivity of the formation with 100% water


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Suppose a container, e.g a tank full of water whose resistivity is 1 ohmThe resistivity (Rw) of this water volume is 1 ohm.

Fill up the tank with sand grains. The water will now occupy the porespace. Measure the resistivity of the total volume (water + grains), we wil

have a resistivity (Ro) greater than Rw. Ro> Rw.

Answer resistivity

Answer resistivity


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Is added to the beans and water a certain amount of oil. The measuredresistivity (Rt) is greater than the previous one (Ro).

Current flows only through the water, which is conductive because its salcontent in solution. The matrix and act as insulating oil. When there is lowporosity there is also little water, then place high resistivity values . Thereforethe porosity is an important factor, as both a porous rock with a rock or HC

closed with water gives high values ofresistivity, confusing the interpreter.

Rt = Resistivity True of Fm. with H2O + Grains + HC

Rt > Ro > Rw


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Zona Invadida

Virgin Zone Rt

Invaded Zone

Ri

Screed Rmc

Mud Rm

Washed Zone RL

horizontal schematic representation of the distribution of fluids within formation near a

well and distribution of radial concentric resistivity in a zone with water.


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Profiles of spontaneous potential andgamma ray

The curve of spontaneous potential (SP) and natural gamma ray log (GR) profiles are physical phenomena tha

occur naturally in rocks "in situ; Spontaneous Potential - The SP curve records the electrical potential (voltage) produced by the interaction o

formation water, drilling fluid and conductive ion selective certain rocks (shales);

Gamma Ray - indicates the natural radioactivity of the formations, which depends on the concentration of uraniumthorium and potassium.

GR standard which measures only the total radioactivity

Registration natural gamma rays spectrometry (NGS), which measures the total radioactivity an

concentrations of potassium, thorium and uranium; Both the SP curve as the record of GR usually represent the left profile. In general, if measuring i

conjunction with any other record, as the resistivity and porosity.


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Information obtained (1) - Differentiates rocks potentially producing, porous and permeable

(sandstone, limestone, dolomite), clays and shales not permeable; (2) - Defines the boundaries of the layers and allows the correlation

between the various layers of a sedimentary basin wells; (3) - Provides an indication of shaliness layer;

(4) Indicates the presence of salt or fresh water;

(5) - Help in Identifying the lithology (mineral); (6) - In the case of the SP curve, allows the determination of resistivity othe formation water, Rw. In certain cases profiles GR or NGS serve todetect and evaluate radioactive mineral deposits.

(7) The NGS profile, it's the defining Concentrations of the potassiumthorium and uranium.


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Curves Spontaneous Potential SP The SP curve is a record, as a function of depth, the difference between the electrical potential of

movable electrode and the electrical potential in the well of a fixed electrode on the surface.


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Behaviors of the materials before

In front of shale, the SP curve generally defines a more or less straight line in the profile, which is calledbaseline shales;

In front of the permeable layers, the curve shows negative excursions with respect to baseline shalethese excursions in thick layers (deflection) tend to achieve a substantially constant deflection, thus alsdefining a line of sand;

The deflection can be developed to the left (negative) or right (positive) mainly depending on thsalinity of the formation water and mud filtrate;

If the salinity of the formation water is greater than that of the mud filtrate, the deflection will be to thleft (negative value). If the salinity contrast is the reverse deflection is to the right. If there is no contrasin salinity deflection shall be void. In this case the horizon will be confused with shale;

The deflections of the curve SP result from electrical currents flowing in the mud pit. Electric currentare of two kinds. Electric current nature of electronic and electrical current of ionic nature. Thesecurrents are due to SP electromotive forces in formations that have an origin ion electrochemical an

electrokinetic.


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THE FIVE BASIC ANSWERS FOR THE SP PROFILES ANDRESISTIVITY FOR ONE LAYER BETWEEN SHALES


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PROFILE GAMMA RAY (GR)

Sedimentary formations in the profile reflects the clay content of thetraining because the radioactive elements tend to concentrate in clays andshales.

The formations cleaner has a very low level of radioactivity, unles

radioactive contaminants such as volcanic ash or waste of granites arepresent or that the waters contain training radioactive salts dissolved.


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Properties of Gamma Rays.

Are pulses high energy electromagnetic waves that are emitted spontaneously bysome radioactive elements. The radioactive isotope of potassium with an atomiweight of 40, and the series of radioactive elements uranium and thorium eminearly all gamma radiation which lies on earth. Each of these elements emitgamma rays and the number and energy of each is separately;

When passing through matter, gamma rays experience Comptom successive

collisions with the atoms of the training material and lose energy in each collisionAfter the gamma ray has lost sufficient energy, an atom absorbs the formationthrough a photoelectric effect. Accordingly, the natural gamma rays are absorbedand its energy gradually degrade (lower) passing through the formations;

The rate of absorption varies with the density of the formation: two configurationhaving the same amount of radioactive material per unit volume, but with differen

densities show different levels of radioactivity; less dense formations appeaslightly more radioactive.


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SONIC PROFILE

record of sound propagation ( t) in different lithologies traversed in awell.

t - is the time required for a sound wave to travel one foot formation;

a velocidade do som varia segundo o meio em que as ondas sepropagam e que estas viajam mais rapidamente em slidos que em

lquidos e so muito mais velozes em lquidos que em gases.


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Sometimes the velocity of sound is a convenience featureto differentiate between different types of lithologies.

EnvironmentSONIC VELOCITY (FOOT/SEC) TRANSIT TIME

(sec./foot)

Sand 18.000 - 19.500 55,5 - 51,2

Limestone 21.000 - 23.000 47,6 - 43,5

Dolomite 23.000 - 26.000 43,5 - 38,5

Anidrite 20.000 50,0

Salt 15.000 67,0

Clay 6.000 - 16.000 167,0 - 62,5

Fresh Water 5.300 189,0

Sea Water 5.000 167,0

Petroleum 4.300 232,0

iron 17.500 57,0


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Application

The sonic profile can be used O perfil snico pode seutilizado in the following cases:

a) Determining the porosity of the formation;

b) Correlation;

c) Identification of lithology;d) Aid in seismic interpretation for developing syntheticseismogram;

e) Indication of fractures;

f) Estimating compaction .


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The Porosity An advantage of the sonic profile come from th

direct relationship between the transit time an

porosity, hence say that the sonic profile serves aregistrar of porosity.

For compacted formations and intergranulaporosity fairly uniform, Willie and others proposethe link below:

t profile = reading the profile

t f = transit time in the fluid ( 189 seg/p)

t ma = transit time in the matrix rock (sand,limestone, dolomite, etc)

matftmatprofilet


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Advantages and Disadvantages of Sonic Profile

Advantages

- Optimistic assessment of porosities (s high) - Little affected by the pore fluids

- Can be registered with IES profiles (resistivity) and RG(Gamma Ray)

- Lets check seismic data Disadvantages

- Affected by shaliness

- Reads only the primary porosity

- It can not be run in cased


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Neutron profile

Preliminarily profiles Neutron account the amount of hydrogen in existing formationsConsequently, the "formations" (rocks) whose pores contain clean water or oil reflecthe value of the porosity filled with liquid.

Gas zones can often be identified by comparing the profile with another profileneutron porosity. The combination of Neutron with one or two other profiles oporosity provides, in fact, porosity values far more accurate lithology identification and

even determination of clay.


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Principle of neutron logging


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Application of the Neutron Logging- Determination of porosity is one of the most important use of neutron profiles. Fixes for lithology an

open pit parameters are required for porosity determinations;

- The SNP is specially designed for use in open pit and provides readings of porosities with minimaeffect of the well. It is the only efficient neutron tool for use in wells filled with gas;

- The CNL is designed for use in combination with other tools open pit or well coated. The feature ogreatly reduces the effects of compensation parameters from the well;

- The GNT can be used in both open pit and in cased. Registered in combination with a gamma curvequalitatively it eliminates the shale formations and closed porous sections;

- In combination with another profile of porosity (pore other data) or use in a graph against thresistivity, the neutron profile is useful for detecting gas zones.

- The neutron profile is used in combination with other porosity profiles for the interpretation olithology.

- The neutron profile is used in combination with other porosity profiles for the interpretation of shalsandstones.


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Dipmeter profiles - devices microresistividade

Determines the plunge and discontinuities (such aslayering, layering of strata traversed, and failures) in thesubsurface.


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Profile dipmeter showing the azimute and dipping layers


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2004-gelog jr


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2010-Geologo Jr.


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2010/2-Geologo Jr.

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Elementos de geofísica de poço