BASIC WELL LOG ANALYSIS FOR GEOLOGISTS PDF

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DOWNLOAD PDF Basic Well Log Analysis for Geologists (AAPG Methods in Exploration 3) Basic Growth Analysis: Plant Growth Analysis for Beginners. As logging tools and interpretive methods are developing in accuracy and sophistication, they are playing an expanded role in the geological. PDF | On Jan 1, , Fadhil Sadooni and others published Basic Well Log Analysis for Geologists Arabic.


Basic Well Log Analysis For Geologists Pdf

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Basic Well Log Analysis for Geologists George B. Asquith, Charles R. Gibson. Basic Well Log Analysis is a general introduction to common openhole logging measurements, both wire line and . Gibson ebook PDF download. Basic Well Log. haakoopmacyding.gq - Ebook download as PDF File .pdf), Text File .txt) or read book online. Basic Well Log Analysis for Geologist - Free ebook download as PDF File .pdf) or read book online for free. A good manual for geologist.

Publisher's Note: Because most new geologists come out of college with little understanding of the industry's primary tool. This selection is the author's and the associated service company is not responsible for its accuracy.

AAPG acknowledges the logging companies and engineers who cooperated with their advice and examples. Because it is important to offer examples in a book of this nature. As a special note of thanks. The book is oriented toward geologists rather than engineers.

In the text and examples. All the to transmit fluids. The different sources create records logs When relative permeability of a formation's water is zero. Permeability is controlled by the size of the knowledge of many parameters. It is essential that the reader understand these zones and to assist with structure and isopach mapping.

Besides their traditional use in exploration to correlate and resistivity. Remember that a borehole represents a refers to the presence of two fluids in a rock. This is not only because of its fluids. Isolated pores different types of logs and their curves discussed in the text and pore volume occupied by adsorbed water are excluded are this type.

Stated differently. In addition. Logging data is Porosity—can be defined as the percentage of voids to used to identify productive zones.

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It is measured as a percent and has thickness of zones. Of the various types of logs. As a consequence. It is related to porosity but is not always dependent lengthy and unfamiliar terminology. For the reader With increasing relative permeabilities to water.

The parameters of log otherwise reduce the ability of other fluids to move through interpretation are determined both directly or inferred the rock. A geologist's first exposure to log interpretation can be a Permeability—is the property a rock has to transmit frustrating experience. In common usage. Professional Well Log Analysts. It is measured in darcies or millidarcies and is logging process is possible. Effective permeability log analysis. The name open hole is applied because these logs are The amount of void space that is interconnected.

The first electric log was run September 5. Resistivity is the measurement of resistance. The higher the value for and are.

In log interpretation. Water saturation which led. At irreducible water saturation. Doll in Alsace-Lorraine. By combining the formulas: In The unit of measure used for the conductor resistivity RJ and the formation resistivity R. Resistance is the Archie's experiments also revealed that formation factors inherent property of all materials. Water saturation—is the percentage of pore volume in a Conrad Schlumberger in began the first experiments rock which is occupied by formation water.

Because during the logging measurements.

Because both the rock and hydrocarbons act as insulators Now that the reader is introduced to some of the basic but saltwater is conductive. The following relationship: Resistivity is measured by to hydrocarbons. The transition or annulus dj. If invasion is deep or moderate.

Sxo] where R. The excess of borehole Flushed Zone Rxo —The flushed zone extends only a pressure over formation pressure prevents blow-outs. Pores in the uninvaded 3.

General invasion diameters are: A well's borehole and the rock surrounding it side of the borehole and form mudcake Rmc. Figure 1 is a schematic illustration of a filtrate Rmf. The resistivity values for drilling mud. The mudcake then acts as a barrier the borehole may be larger or smaller than the bit diameter to further invasion. When oil is present in the some of the drilling fluid to invade porous and permeable flushed zone. The definitions of each of the symbols used in Figure 1 Invaded Zone-The zone which is invaded by mudfiltrate are listed as follows: Fluid are contaminated by the drilling mud.

The Hole Diameter dh —A well's borehole size is described solid particles in the drilling muds coalesce and form an by the outside diameter of the drill bit. The size of the borehole is measured by a caliper be affected.

It consists of a flushed zone Rxo dh. As invasion occurs. The flushed zone Rxo occurs close to the borehole Fig. In general. Drilling Mud Rm —Today. This pressure difference forces Rw by mud filtrate Rmf. Figures 6a and 6b illustrate the resistivity curves while deeper reading. A freshwater mud i.

They are of particular interest because. Sw and the flushed zone's water saturation Sxo is an Water-Bearing Zones—Figure 4 illustrates the borehole index of hydrocarbon moveability.

Because of their importance. Shallow reading. A saltwater mud i. A hydrocarbon zone invaded with uninvaded zones Rxo. In some instances. It is probably a more realistic model for true borehole zones where the resistivity of the mud filtrate Rmf is much conditions than the step profile. There are three results in a "wet" log profile where the shallow R xo. By using freshwater mud results in a resistivity profile where the these three resistivity measurements.

As the mud filtrate invades the saturated with formation water R w. The formula for calculating hydrocarbon Log resistivity profiles illustrate the resistivity values of saturation is: The annulus profile is detected only by an induction log run soon after a well is Basic Information Needed in Log Interpretation drilled. Figures 7a and 7b illustrate the resistivity curves for hydrocarbon An annulus profile is only sometimes recorded on a log zones invaded with both freshwater and saltwater muds.

The transition profile also has a cylindrical geometry with Hydrocarbon-Bearing Zones—Figure 5 illustrates the two invasion diameters: A three resistivity curves are: Even in hydrocarbon-bearing reservoirs. They illustrate the horizontal approximately equal to the resistivity of the formation water distributions of the invaded and uninvaded zones and their Rw in saltwater muds. All the variations and their The ratio between the uninvaded zone's water saturation associated profiles are illustrated in Figures 4 and 5.

Two modern resistivity devices which use these When this happens. Water saturation filtrate forming an annular circular ring at the edge of the S w. These three invasion profiles are record high R xo. These profiles vary. The annulus effect is detected by a reservoir evaluation because. Texas-Louisiana chart is closely approximated by the Arp's formula: Gulf Coast after Carothers and Porter.

As a Where: Southern different fluids Rm. Porosity logs The formation temperature is also calculated Asquith. Figure 9 is a chart that is used for Porter. The temperature of a formation is determined by knowing: AW formation as mud filtrate Rraf.

The Archie equation for water saturation is: Pf uninvaded zone R t. The resistivities of the drilling mud R m. The four most fundamental rock properties used in producing well. Formation Factor: Chapter I 1.

Table 2 is a list of fundamental equations that are used for Where: The four fluids that affect logging measurements are: The often equals 2. Where a porous and permeable formation is Porosity: Formation water resistivity Rw is also determined water saturation. The lithology of a formation must be known because: Fundamental Equations of Well Log R.

Formation Water Resistivity: Copyright Dotted lines indicate the cylindrical nature of the invasion. This schematic diagram illustrates an idealized version of what happens when fluids from the borehole invade the surrounding rock. The borehole environment and symbols used in log interpretation. Figure 1. Schlumberger Well Services. Temp Rmc Meas. Log Measured From. Other Services: Datum Elev. Temp Source: Rmf Meas. Depth-Driller Depth—Logger Btm. Information on the header about the resistivity values for drilling mud Rm and mud filtrate Rmf are especially useful in log interpretation and are used in calculations.

Reproduction of a typical log heading. Remember that true resitivity of a formation can be measured in the uninvaded zone because of its virgin nature. Resistivity of the uninvaded zone is Rt if hydrocarbon-bearing or R. When an annulus profile is present. Thus the resistivity reads high. The resistivity of the invaded zone's flushed part is Rxo. Formation water has been pushed ahead by the invading mud filtrate into the annulus zone.

Beyond the outer boundary of the invaded zone is the annulus zone where pores arefilledwith residual hydrocarbons RH and formation water Rw. In this diagram. As mud filtrate Rmf moves into a porous and permeable formation. In the transition part of the invaded zone. Typical invasion profiles for three idealized versions of fluid distributions in the vicinity of the borehole.

The annulus profile represents a fluid distribution which occurs between the invaded zone and the uninvaded zone and denotes the presence of hydrocarbons.. In the flushed part Rxo of the invaded zone. Pores beyond the flushed part of the invaded zone R.

Here again invasion is cylindrical. In the invaded zone. Various fluid distributions are represented by the step.

Transition Profile—This is the most realistic model of true borehole conditions. Annulus Profile—This reflects a temporary fluid distribution. This causes a temporary absence of hydrocarbons which. The resistivity of the invaded zone is Rxo. The diameter of the cylinder is represented as dj. The cylindrically shaped invaded zone is characterized by its abrupt contact with the uninvaded zone.

True resistivity R will be higher than the wet resistivity R0 because hydrocarbons have a higher resistivity than saltwater.

Beyond the outer boundary of the invaded zone dj on diagram. Beyond the annulus is the uninvaded zone where pores are filled with formation water Rw and hydrocarbons. The abrupt resistivity drop is due to the high concentration of formation water Rw in the annulus zone. Step Profile—Mud filtrate is distributed with a cylindrical shape around the borehole and creates an invaded zone.

In the uninvaded zone. Freshwater Muds—The resistivity of the mud filtrate Rmf is greater than the resistivity of the formation water Rw because of the varying salt content remember.

The geologist needs to be aware that a difference exists. With a water-bearing formation. Horizontal section through a permeable water-bearing formation and the concomitant resistivity profiles which occur when there is invasion by either freshwater.

To find out which mud is used in your area. The type of mud used affects the log package selected. These examples are shown because freshwater muds and saltwater muds are used in different geographic regions. The flushed zone Rxo. Away from the borehole. A general rule when freshwater muds are used is: Resistivity of the uninvaded zone is greater than the resistivity of the invaded Rj zone. Away from the borehole as more hydrocarbons mix with mudfiltratein the invaded zone. Such a mixture causes high resistivities.

Beyond its flushed part Rxo. Horizontal section through a permeable hydrocarbon-bearing formation and the concomitant resistivity profiles which occur when there is invasion by either freshwater. To summarize: Freshwater Muds—Because the resistivity of both the mudfiltrate Rmf and residual hydrocarbons RH is much greater than formation water Rw.

The resistivity of the uninvaded zone R. In some cases. The presence of hydrocarbons in the uninvaded zone causes higher resistivity than if the zone had only formation water Rw. In water-bearing zones in this case from 5. Example of Dual Induction Focused Log curves through a water-bearing zone. This is a measure of the uninvaded zone.

In a water-bearing formation. Ignore the left side of the log on the opposite page. See Figure 4 for review. Resistivity values are higher as distance increases from the left side of the log. In a water-bearing zone.

IX- fr r! T SEL Mon. Depth Rmf at me s temp. Because Rmf is approximately equal to Rw. In water-bearing zones in this case from 9. In water-bearing zones the curve will record low resistivity because saltwater mud filtrate has low resistivity. Example of Dual Induction Focused Log curves through a hydrocarbon-bearing zone. See Figure 5 for review.

In hydrocarbon-bearing zones in this case from 8. In a hydrocarbon-bearing zone. This resistivity is normally equal to or slightly more than the deep induction curve ILD. Log Curve ILD—Deep induction log resistivity curves measure the true resistivity Rt or the resistivity of the formation deep beyond the outer boundary of the invaded zone. Thermometer Broke RM at m e n s temp: In hydrocarbon-bearing zones in this case from 9. The reason for the increase in resistivities deeper into the formation is because of the increasing hydrocarbon saturation.

In hydrocarbon-bearing zones. V' feH. W rn ffittg w: Follow the temperature gradient line up to 6. Chart for estimating formation temperature Tf with depth linear gradient assumed. Dresser Atlas. Dresser Industries. This intersection defines the temperature gradient. VM3dW3X Locate the resistivity value. Resistivity of drilling mud Rm equals 1. Use the chart on the opposite page. From point B.

Because resistivity varies with changes in temperature. In spontaneous potential log is used to identify impermeable water-bearing zones the amount of SP reduction is zones such as shale. For example. DC voltage differences between the naturally occurring The SP response of shales is relatively constant and potential of a moveable electrode in the well bore.

It is measured in millivolts. Permeable zones are indicated where there is SP deflection Electric currents arising primarily from electrochemical from the shale baseline. The spontaneous potential SP log was one of the earliest Borehole and invasion—Hilchie indicates that the electric logs used in the petroleum industry. The text discusses value less than SSP Fig. Primarily the formation reduces the SP deflection Fig.

Permeable bed boundaries formation water resistivity Rw within permeable beds. In However. The magnitude of track 1 and is used to: The SP value resistivities obtained from the log heading of the mud that is measured in the borehole is influenced by bed filtrate Rmf and drilling mud Rm to formation thickness. SP curve potential of a fixed electrode located at the surface Doll. SSP is determined by find a value for Rw by the following procedure: After you formula or chart and is a necessary element for determining determine the formation temperature.

As a well bore and surrounding formations. In this example. By far the largest number of wells today have Shale content—The presence of shale in a permeable this type of log included in their log suites. SP log to operate. Equivalent resistivity Rwe is obtained by has less deflection in hydrocarbon-bearing zones. A careful examination of Figures should 2 resistivity from the shallow-reading resistivity tool R.

Instead of charts. Rmfe stands tor equivalent resistivity.

Where Rmf is greater than Rw, the SP line kicks to the left of the shale baseline negative deflection. Where Rmf greatly exceeds Rw, the deflection is proportionately greater. Where Rmf is less than Rw, the kick is to the right of the shale baseline. This is called positive deflection. Remember, the spontaneous potential log SP is used only with conductive saltwater-based drilling muds.

All other deflections are less, and are relative in magnitude. PSP pseudo-static spontaneous potential is the SP response if shale is present. Note at bottom of diagram: A formula for the theoretical calculated value of SSP is given.

Figure This example is an exercise involving the charts on Figures 12 through It is measured here as two 20mv divisions from the shale baseline. The deflection is negative, so the value mv is negative. Bed thickness equals 8 ft 7, to 7, ft.

Resistivity short normal Ri equals 28 ohm-meters. Formation depth equals 7, ft. Your answers should be: It measures two units at a scale of 20 mv per division from the shale baseline.

The deflection is negative, so your answer is also —40 mv negative. Bed thickness read from SP log Fig. Correction factor from Fig. The term short normal describes a log used to measure the shallow formation resistivity, or the resistivity of the invaded zone R;.

For the exercise in Figure Locate a bed thickness on the vertical scale in this case 8 ft. Drop vertically from this intersection and read the SP correction factor on the scale across the bottom in this example. Drop vertically from this intersection and read the ratio value on the bottom scale in this example. Locate an SSP value on the vertical scale in this case mv.

PI HEtfti. K y r-t: JE S mm. Pffl Chart for determining a resistivity value for Rw from Rwe. Locate the value of Rwe on the vertical scale in this case 0. Drop vertically from the intersection and read a value for Rw on the scale at the bottom in this case 0. The SP response in shales is relatively constant and its Where: The variations in the SP are the result of an electric a permeable zone by the following formula: The spontaneous potential log SP can be used to: The SP curve can be suppressed by thin beds.

313383850-Basic-Well-Log-Analysis-for-Geologists.pdf

The SP log can be used to calculate the volume of shale in 2. These The short normal tool has an electrode spacing of 16 secondary currents flow as ground loop currents inches and can record a reliable value for resistivity from a perpendicular to the axis of the borehole Fig.

Figure 16 is a chart which assists in Where: The presence of invasion is important constant intensity. The receiver signals are essentially proportional to tool works best in conductive.

Basic Well Log Analysis For Geologists

Because the short normal coils. The most common type of logging device is the the short normal is compared with the resistivity of the induction tool Dresser Atlas. Electrodes in the borehole are connected to a zones. By far the most important use of resistivity logs is A second type of resistivity measuring device is the the determination of hydrocarbon versus water-bearing electrode log. The two types of induction devices are determine hydrocarbon versus water-bearing zones. Rj from the short normal curve.

I nearby formations. Examples of Hydrocarbons. In addition to providing a value for the resistivity measurement to minimize the effect of Rj. When the resistivity of 4. The alternating magnetic field which is because it indicates a formation is permeable. The short normal curve is usually create magnetic fields that induce signals to the receiver recorded in track 2 Fig. Boreholes filled with Archie equation: Because the rock's matrix or grains are power source generator. The multiple coils are used to focus environment for its use.

A geologist. This log Fig. An track 3 conductivity curve is necessary to more accurately example of the procedure is presented in Figure Hilchie Normal logs E. The diameter of invasion d. The Dual which induces currents in the formation. Resistivity values obtained from the three curves on a Dual The induction curve on the Induction Electric Log Induction Focused Log are used to correct deep resistivity appears in track 2 Fig.

Lateral Log'1' F. Because of deep ceiver spacing of 40 inches and can measure a reliable value invasion. Classification of Resistivity Logs. The modern induction log is called the Dual Induction induction—The induction device Fig. These induced Induction Focused Log Fig. Because the induction log does not Focused Log are recorded on a four cycle logarithmic scale require the transmission of electricity through drilling fluid.

This is because the filtrate has invaded the formation. The micro normal from flowing up the borehole filled with saltwater mud device investigates three to four inches into the formation Fig. Under these conditions. The procedure is illustrated in Figure The technique is called Rt minimum R. A current from the surveying electrode that primarily detects mudcake Hilchie.

The pad is is forced into the formation by focusing electrodes. Both are displayed in tracks 2 Where: A tornado chart Fig.

The measurements are made. Because saltwater-based mud the rock matrix. To verify these invasion. The in contact with the borehole and consists of three electrodes focusing electrodes emit current of the same polarity as the spaced one inch apart.

From the pad. The borehole size and formation the mudcake.

Rxo is affected by the unflushed residual hydrocarbons left Shallow resistivity devices. Hilchie states that resistivities of approximately ten times the resistivity of the solve for F: To correct for residual hydrocarbons in the flushed zone.

In order to detect zones of erroneous positive separation. Where the pad is in contact a with the formation. Nonporous and impermeable zones have high resistivity values on both the micro normal and micro 1. Porosity in a water-bearing formation can be be related to porosity by the following: Sxo v v "TO mf 'Fx now square both sides: Rj are used to determine porosity. These residual hydrocarbons include the following: A formation's resistivity can be measured by either Table 5.

Resistivity logs are used to: Schematic illustration of a basic two-coil induction system. See Table 5 for examples. SchlumbergerWell Services. Most minerals which make up the matrix of the rock and the hydrocarbons in the pores are non-conductive. Chapter III Where: High gravity oil 40 to 50 10 to 5 90 to 95 4. By use of tornado charts. Low gravity oil 10 to 20 30 to 20 70 to 80 5. The scale values increase from left to right. On this and all subsequent logs in the text.

The induction log actually measures conductivity. This is done automatically as the log is recorded in track 3. One measures shallow resistivity R. The first scale measures from 0 to 50 ohm-meters in increment values of 5 ohm-meters. The second-cycle scale measures from 0 to ohm-meters in increment values of 50 ohm-meters. The induction reading on track 2 is counted at 10 ohm-meters. It contains no curves in this example because the second-cycle scale is used only when the resistivity curves in the first-cycle scale exceed the maximum scale values.

Because the deflection is to the left negative deflection the log value is negative. Because resistivity equals 1.

Note that log scales are shown horizontally at top of log. In this way. This first scale contains both the Ri and R. Track 2—The middle log track contains two resistivity curves. Track 3—The log track on the far right contains a conductivity curve measured by the induction log. This is counted horizontally as almost 6 increments of 5 ohm-meters per increment 28 is nearly 6 x 5 or Track 1—The log track on the far left contains the spontaneous potential SP log. The values on the conductivity scale increase from right-to-left.

Example Induction Electric Log. At the sample depth of 7. MF at mioi. Example of a Dual Induction Focused Log. The gamma ray. The resistivity scale in tracks 2 and 3 is a logarithmic scale from 0 to 2. At the sample depth in this exercise Track 1 in this log suite contains a gamma ray. Use this log to pick values and determine ratios for the tornado chart exercise in Figure The following ratios are needed for work on the tornado chart Fig.

Note the following logs. By using the tornado chart. Schlumberger Given: This ratio. Note that the scale decreases in intensity from left to right from 1. The scale is indicated by the dashed. Log values used in this exercise are picked from the example Dual Induction Log in Figure The scale is represented by the solid. Where the values cross. As cited in the example. The monitoring electrodes M. A] above and A2 below are the focusing or guard electrodes which direct and force the current from the A0 electrode into the formation.

Rnn at mtos. Gamma ray logs are discussed in a later chapter. There is no second cycle recorded. Track 1—The log track on the far left in this example is a gamma ray log. At the sample depth of 3. The purpose for presenting this log is to illustrate the log curves. These logs are used when Rmf — Rw. Note that the scale increases from left to right. Note that the scale starts with zero between tracks 2 and 3—that is.

The scale ranges from 0 to 50 ohm-meters in increments of 5 ohm-meters. Thermometer Broke RM ot meas temp. V4 RMC at meas. These logs are used when Rnlf — Rw and invasion is deep. The resistivity scale in tracks 2 and 3 is a four-cycle logarithmic scale ranging from 0 to 2.

At the sample depth of this exercise 9. Use this log to pick values and determine ratios for the tornado chart in Figure At the sample depth in this exercise 9. Our value falls between the scale values 1. Our value falls between the scale values of 30 and 40 inches. The scale values read from bottom to top on the left part of the chart. Determine subsequent ratio values from the tornado chart. The scale values read across the top part of the tornado chart.

Our value falls between the scale values 3 and 5 much closer to 5. Track 2—Note the positive separation between the micro normal log and the micro inverse log.

The combination of mud filtrate. Positive separation is indicated where the resistivity value of the micro normal log shown by the dashed line is greater than the resistivity value for the micro inverse log shown by the solid line.

Examine the log from a sample depth 5.

This higher micro normal resistivity value is because the micro normal curve reads deeper into the flushed zone. This log demonstrates permeability two ways: Track 1—Note that the caliper shows a borehole diameter of approximately 11 inches just above the sample depth. In this example the scale is logarithmic.

The caliper log indicates a borehole slightly less than 9 inches. Examine the log curves at the sample depth of 4. Micro inverse has a value of about 1. This particular log package includes: At the sample depth of 4. Anhydrite A Atma Table 6. This will happen feet per second. A sonic derived than vuggy or fracture secondary porosity. These devices greatly reduce the spurious porosity can be used to determine porosity in consolidated effects of borehole size variations Kobesh and Blizard.

The interval transit time At is dependent upon both called SPI or secondary porosity index. Total porosity contains a caliper log and a gamma ray log or an SP log values are obtained from one of the nuclear logs i. The percentage porosity curve is sometimes recorded in tracks 2 and 3. If the effect of hydrocarbons is not corrected. The percentage of secondary porosity. Interval transit time At is recorded in because the sonic log only records matrix porosity rather tracks 2 and 3 example Fig.

These constants are used in the Sonic Porosity Formula after Schlumberger. Track 1 normally subtracting sonic porosity from total porosity. A lowering of neutron porosity by must be known.

In clean formations i. It can assist the geologist to: Neutron log responses vary. Because the Neutrons are created from a chemical source in the modern density log is a compensated log dual detectors. A density derived porosity curve is neutron collides with a hydrogen atom. Whenever the correction formation material.

Hilchie suggests using a gas between incoming gamma ray particles and electrons in the density of 0. Matrix Densities of Common Lithologies.

Compton Scattering. These variations in response can be compensated for by Where: Tittman and Wahl called the interaction does gas effect. Because the hydrogen atom is almost equal in obtainedfrom the bulk density curve pb should be mass to the neutron. The formation density log is a porosity log that measures electron density of a formation. The number of Compton Scattering collisions is a Neutron Logs direct function of the number of electrons in a formation Neutron logs are porosity logs that measure the hydrogen electron density.

The chemical source may be a mixture the correction curve Ap. The gamma ray source is either Cobalt or Cesium Track 1 contains a formation's hydrogen concentration.

See a Problem?

Where invasion of a formation is shallow. Because hydrogen in a gamma ray log and acaliper example. Scattered gamma rays porosity formula if gas density is unknown.

The formula for calculating density gas is called gas effect. These neutrons collide with the nuclei of the due to borehole irregularities. This occurs porosity. Anhydrite 2. To determine density water. Formation bulk density pb is a function of matrix energy loss can be related to the formation's porosity. By identifying rock type porosity log. This calculated detector in a pad which is pushed against the side of the porosity value compares favorably with the value obtained borehole.

Besides its use as a porosity device. Gas effect is created by gas in the pores. Figure 35 also illustrates the change in neutron-density The Neutron-Density Log consists of neutron and density response between an oil. The Sidewall Neutron Log has both the source and formula. Figure 36 is a schematic illustration of a Gamma Ray Examination of the neutron-density porosity chart Fig. The observed on the Neutron-Density Log.

Both the Sidewall and Compensated formula should be used to determine neutron-density Neutron logs can be recorded in apparent limestone. The procedure is identical for each of the charts and is shown in Figures 30 and Neutron-Density Log through several gas sands.

It 34 reveals that the porosity values are only slightly affected illustrates how changes in porosity. The example from Figures 32 and If a formation is limestone. The most modern of the neutron logs is a from the crossplot method. Figure 35 is a schematic illustration of how lithology affects the Combination Gamma Ray Neutron-Density log. If the neutron and density porosities from Figure 32 at a The first modern neutron log was the Sidewall Neutron depth of 9. The oil. In contrast. In the concentration of hydrogen atoms than oil or water.

Both the density log reading of four porosity units more than the neutron and density curves are normally recorded in neutron log. The advantage of Compensated Neutron logs porosity of less than 0. Compensated Neutron Log which has a neutron source and Whenever a Neutron-Density Log records a density two detectors.

Bulk density. The formation's electron log. Porosity can be determined from a Neutron-Density density is related to a formation's bulk density pb in Log either by a crossplot chart or by formula. Log are: In gas reservoirs. Interval transit time is lower hydrogen ion concentration than oil or water gas related to formation porosity. Additional uses of the combination Neutron-Density porosity. The density log is a porosity log that measures the 6.

The sonic log is a porosity log that measures the log can be related to water-filled porosity. The neutron log is a porosity log that measures the determination of lithology. Chapter IV 1. In shale-free density. The three types of porosity logs are: But, the diameter of impermeable mudcake. The mudcake then acts as a barrier the borehole may be larger or smaller than the bit diameter to further invasion. The size of the borehole is measured by a caliper be affected.

General invasion diameters are: log. The excess of borehole Flushed Zone Rxo The flushed zone extends only a pressure over formation pressure prevents blow-outs. If invasion is deep or moderate, most often the hydrostatic pressure in the mud column is always greater flushed zone is completely cleared of its formation water than formation pressure. This pressure difference forces Rw by mud filtrate Rmf. When oil is present in the some of the drilling fluid to invade porous and permeable flushed zone, you can determine the degree of flushing by formations.

As invasion occurs, many of the solid particles mud filtrate from the difference between water saturations in the flushed Sxo zone and the uninvaded Sw zone Fig. As the mud filtrate invades the saturated with formation water R w , oil, or gas. Even in hydrocarbon-bearing reservoirs, there is always a Next, formation water is pushed out in front of the mud layer of formation water on grain surfaces. Water saturation filtrate forming an annular circular ring at the edge of the S w ; Fig.

The annulus effect is detected by a reservoir evaluation because, by using water saturation higher resistivity reading on a deep induction log than by data, a geologist can determine a reservoir's hydrocarbon one on a medium induction log. The formula for calculating hydrocarbon Log resistivity profiles illustrate the resistivity values of saturation is: the invaded and uninvaded zones in the formation being investigated.

These profiles vary, depending on the relative resistivity values of Rw and Rmf. All the variations and their The ratio between the uninvaded zone's water saturation associated profiles are illustrated in Figures 4 and 5. Sw and the flushed zone's water saturation Sxo is an Water-Bearing ZonesFigure 4 illustrates the borehole index of hydrocarbon moveability.

They illustrate the horizontal approximately equal to the resistivity of the formation water distributions of the invaded and uninvaded zones and their Rw in saltwater muds. A freshwater mud i. There are three results in a "wet" log profile where the shallow R xo , commonly recognized invasion profiles: 1 step, 2 medium Rj , and deep Rt resistivity tools separate and transition, and 3 annulus.

These three invasion profiles are record high R xo , intermediate Rj , and low Rt illustrated in Figure 3. A saltwater mud i. Shallow reading, resistivity R; , and deep Rt resistivity tools all read low resistivity logging tools read the resistivity of the invaded zone R, , Fig.

Figures 6a and 6b illustrate the resistivity curves while deeper reading, resistivity logging tools read true for wet zones invaded with both freshwater and saltwater resistivity of the uninvaded zone Rt. The transition profile also has a cylindrical geometry with Hydrocarbon-Bearing ZonesFigure 5 illustrates the two invasion diameters: d; flushed zone and dj transition borehole and resistivity profiles for hydrocarbon-bearing zone.Example crossplot of formation resistivity R.

The enormous importance of logging dictates that as geologists. Valuesfromthis log are used in work Table A. From point B. The resistivity of the invaded zone is Rxo.