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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. chronanreareeko.cf - 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.

And, all saturation and is a function of porosity, type of fluid i. Because both the rock and hydrocarbons act as insulators Now that the reader is introduced to some of the basic but saltwater is conductive, resistivity measurements made concepts of well log interpretation, our discussion can be by logging tools can be used to detect hydrocarbons and continued in more detail about the factors which affect estimate the porosity of a reservoir. Because during the logging measurements. A well's borehole and the rock surrounding it side of the borehole and form mudcake Rmc; Fig. Fluid are contaminated by the drilling mud, which affects logging that filters into the formation during invasion is called mud measurements. Figure 1 is a schematic illustration of a filtrate Rmf; Fig. The resistivity values for drilling mud, porous and permeable formation which is penetrated by a mudcake, and mud filtrate are recorded on a log's header borehole filled with drilling mud. The definitions of each of the symbols used in Figure 1 Invaded Zone-The zone which is invaded by mudfiltrate are listed as follows: is called the invaded zone.

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. 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: The unit of measure is porosity than the formation's true porosity because gas has a microseconds per foot ju. The Neutron-Density Log is a combination porosity electron density of a formation.

Note that the gamma ray scale reads from 0 to API gamma ray units. Example sonic log with gamma ray log and caliper. The gamma ray scale is represented by a solid line. Sonic log interval transit time At is represented by a solid line. The sonic porosity measurement limestone matrix is shown by a dashed line. The caliper scale ranges from 6 to 16 inches. Track 1—This track includes both the gamma ray and caliper curves. This example is shown to display the scales of a sonic log.

At the sample depth used in Figure 27 9. Tracks 2 and 3—Both the interval transit time At scale and the porosity scale are shown in this track. Follow the value 63 vertically until it intersects the diagonal line representing In this case. From that point. Chart used for converting interval transit time At values to sonic porosity. The formation factor curve F ranges in value from 1 to Example of a bulk density log with a gamma ray log and caliper. The bulk density p. Track 1—This track includes both the gamma ray and caliper logs.

This log is presented to show you the scales of a density log. At the sample depth used in Figure 29 9.

Note that both scales read left-to-right. The correction Ap. The density log correction curve Ap ranges in value from Tracks 2 and 3—The bulk density curve pb. Follow the value vertically until it intersects the diagonal line representing the matrix density pma used in this case 2. Find a value for bulk density pb on the horizontal scale at the bottom of Figure 29 in this example 2. Follow the value vertically until it intersects the diagonal curve representing dolomite. The lithology is dolomite.

Follow the value vertically until it intersects the diagonal curve representing lithology in this case. The lithology is sandstone.

At the sample depth of 9. The scale for both is the same. Note that the gamma ray sc ale reads from 0 to API gamma ray units and the caliper measures a borehole size from 6 to 16 inches. Figures 33 and 34 are charts and examples for correcting Neutron-Density Log porosities for lithology. Example of a Combination Neutron-Density Log with gamma ray log and caliper. Because salt versus freshwater drilling muds can affect the porosity values.

This log illustrates the log curves and scales of a combination log. Track 1—This track contains both gamma ray and caliper curves. TTTT 4 0 10 20 Density Logs. Follow the values until they intersect on the chart. Chart for correcting Neutron-Density Log porosities for lithology where saltwater-based drilling mud is used where Courtesy.

This figure shows sample relationships between log responses and the rock type. Schematic illustration of neutron-density responses in gas-bearing sandstones modified after Truman et al. Generalized neutron-density log responses show how gas effect varies with depth of invasion. Older rocks. From Figure Calculation of the gamma ray index is the first step Review. Chapter V needed to determine the volume of shale from a gamma ray 1. As shale content increases..

The volume of shale is also calculated mathematically Besides their use with identifying lithologies and from the gamma ray index IoR by the following Dresser correlating zones. Shale-free sandstones and carbonates. Gamma ray logs are lithology logs that measure the log the following formula from Schlumberger.

Gamma ray logs are used to: The located on the chart in Figure Because radioactive material is concentrated in shale. Tertiary rocks. The gamma ray log is recorded in track 1 example. The tension curve is a log that measures how much weight is being pulled on the wireline during logging.

Bulk density pt. This example illustrates the curves and scales of a gamma ray log. Example density log with gamma ray log. Note that the scale increases from left-to-right. Next pick the minimum gamma ray reading from the log The correction curve Ap is represented by a dotted-and-dashed line and ranges from At the example depth of Figure 38 Tracks 2 and 3—These tracks include logs representing bulk density pb.

It is 28 gamma ray units the scale measures in increments of 15 units. It is represented by a broken line and ranges from 2.

Track 1—The gamma ray log is the only one represented on this track. INE s s Drop to the scale at the bottom and read the values for the two intersections measured in percent of shaliness. Tertiary rocks and curve 2 representing consolidated. Chart for correcting the gamma ray index IGR to the volume of shale Vsh.

Using the formula see text. Follow the value horizontally to where it intersects curve 3 representing unconsolidated. Pickett and S Hinglecrossplots. Water saturation of the flushed zone Sxo can be used as an indicator of hydrocarbon moveability.

Log parameters can help evaluate a zone and Water saturation of a formation's flushed zone Sxo is determine whether a well completion attempt is warranted. Methods discussed are: This statement temperature is.

Chapter I the flushed zone Sxo. This is true transition type invasion profile may be indicated and Sw regardless of whether or not a formation contains Archie is considered a good value for Sw. Rxo is too high because of the effect of adjacent. This can be very helpful in log analysis because. When Sw is divided by Sxo. Whenever the ratio of SJSxo is less than 0. In this case a more accurate flushed zone of formations with moderate invasion and value for water saturation can be estimated using the "average" residual hydrocarbon saturation.

Method 4. Rxo is too low because invasion is very shallow. A comparative chart. Very Fine 0. In water-bearing zones. Beaver Creek Field. Fine 0. This calculated value for SP should duplicate When a zone is at irreducible water saturation. Modified after: Fertl and Vercellino. From General—Quick look methods are helpful to the Chapter I. North Dakota. The four quick look methods which will be discussed are: Tkble 8. Chapter I. The procedure is as follows. Low Rwa values are recorded on Chapter VIII.

Rwa can also be applied as a VIII. An advantage of an Rwacurve. Chapter hydrocarbon detection. The resistivity porosity formula for The formulas are as follows: Water-bearing zones: Rwa is a value for Rw whenever Sw overlay to the SP curve. A value for R. This deflection to the right. A Pickett crossplot is 0 developed by plotting porosity values with deep resistivity Where: The Dresser Atlas formula is: The Pickett method is based on the observation that true resistivity R.

By engineer can plot R0 as an overlay on the resistivity log. On the plot. By using values 0. When a formation's Rw is known. Data plotted above quick look curves. A scale is constructed with higher porosity Pickett Crossplot Method values on the left.

The values of various water temperature saturation lines Fig.. Table 1 determined as follows: Water-bearing zones then show up as a The Pickett crossplot Pickett.

Determining Therefore: Table 9 and Fig. Table 9. On Figure Select the correct crossplot graph paper Fig. Calculate a value for Rw from any corresponding set several matrix values Atma or p ma until the R. By such trial and error. The resistivity scale can be changed.. This is already Table 9. A geologist should try 6. Evaluate S w values for all the points plotted on the sure to select the scale so that the maximum porosity log crossplot.

As other points are added. Morrow Sandstones. Cimmarron have a better picture of the range of water saturations for the County.

Resistivity Crossplot plotted on Figure Construct a straight line through the most northwesterly points Fig. Scale the x axis on a linear scale. When At — Atma or p m a — p b are plotted versus R. The lines of constant Sw Fig.

Determine lines of constant S w based on the formula: The procedure for constructing a Hingle crossplot to determine water saturation is: Remember that all lines of constant Sw must be constructed 1.

This is also true if a reservoir's water. Atma 4 4. In Figure K equals formulas: Rt in. Coates and Dumanoir formula. By using comparisons of log-derived permeabilities from several wells.

If the values are not constant. When a geologist evaluates a formation by using log-derived permeability Where: The adjusting by constants for the effect hydrocarbon density hydrocarbon-bearing Morrow sand from 4. C and W. When a formation's bulk volume water values calculate permeability Coates and Dumanoir.

These erroneous values are not limited to Unlike the Wyllie and Rose formulas. Whenever shale is present in a formation. The 0. The net result is that if enough shale is present in a reservoir.

Older rocks consolidated: After the volume of shale Vsh is determined. The only exception to this is the density log. Pi to significantly affect log-derived water saturations. O-Sw xhx0xR. Schlumberger, This chapter discussed several log interpretation techniques. These techniques are based on many of the V5h V. The 4. Bulk volume water BVW is important because it percentage of shale is not the critical factor, rather, it is indicates when a reservior is at irreducible water saturation clay's cation exchange capacity Hilchie, , because Nvirr - cation exchange capacity greatly affects resistivity of the 5.

Quick look methods are important because they clay. Kaolinite and chlorite have extremely low cation provide "flags" which indicate zones of potential interest. Hingle and Pickett crossplot techniques are simple exchanges. Therefore, montmorillonite and illite lower and rapid methods for determining: This assumption is not 7. Log derived data can be used to estimate permeability always correct. Most shaly sand interpretation problems occur in 8. Where provide an index of where different pieces of information formation water is very salty, shale has less effect on the are located.

Therefore, calculated water saturations, without correction for shale, are close to true formation water saturation. Crossplot of porosity versus water saturation used to determine bulk volume water. Because production of water in a well can affect a prospect's economics, it is important to know the bulk volume water and whether the formation is at irreducible water saturation Swiri. When values of bulk volume water plot along hyperbolic lines or, in other words, are constant or close to constant, the formation is homogeneous and close to irreducible water POROSITY , 0 saturation Sw irr.

Remember, a reservoir at Sw irr will not produce water. As the amount of formation water increases, the bulk volume water values become scattered from the hyperbolic lines and the formation has more water than it can hold by capillary pressure.

Thus more water is produced relative to oil. Note the scatter of crossplot values from the hyperbolic lines in Figures 39B and 39C. Example taken from the Morrow sandstone. In computing Rw from R. Use the chart to find wet resistivity R0 which can be used to compute Rw. Cimarron County. Follow the value vertically down from the intersection to the Rjm scale at the bottom. Example of a resistivity versus porosity Pickett crossplot.. Note that this crossplot is for use in plotting sandstones.

Example of a resistivity-versus-porosity Hingle crossplot. This crossplot example was intentionally left blank so it can be used by the reader to construct a Hingle plot. A similar. This crossplot example was intentionally left blank so it can be used by the reader to construct a Hingle plot Note that this crossplot is for use in plotting carbonates. Density Log. In step 2 of the text. Before using the Hingle crossplot to determine water saturation Sw for a well-completion decision see text.

Morrow sandstone. This exercise Fig. Example of a resistivity versus porosity Hingle crossplot. Chapter IV: The vertically oriented curved line on which this point falls represents permeability.

Follow the two values into the chart to the point where they intersect. Data points from zones not at Sw irr will scatter from this pattern. On the chart. The diagonally oriented. It is important to remember that this chart is only validfor estimating permeability K in zones at irreducible water saturation Swirr. It helps differentiate shales high and density logs. A sonic log. Note in are: They River Formation in Richland County.

Of course. These lithologic and facies mapping. The sonic log is a porosity log Chapter radioactivity from sands. The density log is a porosity device that neutron log. Whenever lithologies are techniques are especially important to a geologist when more complex. Courtesy Schlumberger Well Services. As a quick look metiiod. Besides their Figure 35 in Chapter IV is a schematic illustration of how importance in completion decisions. Combination Gamma Ray values are essentially independent of matrix porosity Table The neutron log is a porosity device that is At is the reciprocal of the velocity of a compressional used to measure the amount of hydrogen in a formation sound wave through one foot of formation.

Figure 45 is a Gamma Ray Neutron-Density Log Six techniques are presented here which can assist through the Ordovician Stony Mountain Shale and Red geologists with lithologic determination and mapping. Interval transit time radioactivity. Chapter IV. Montana Fig. Compensated Neutron or Sidewall Neutron Once obtained. The spontaneous potential SP log Chapter II can be Notice that two of the data points are above the used to map clean sands shale-free versus shaly sands.

The three points that plot above Richland County. Crossplot charts. Montana at a depth of Lithology is defined by the end-members: Data from this interval.

The data various minerals Table Richland County.. Types of Carbonate Rock Type in a sandstone can cause a loss of permeability. The problem with alpha mapping from an SP log is that At interval transit time vs. Bed thickness problems are minimized by making an SP Rt deep resistivity vs.

Because the bioherm fades crossplot. Rt deep resistivity vs. Table 12 is a list of the crossplots applied by environments. Because shales are more radioactive than clean lithology relationships only when petrographic data is sandstones or carbonates Chapter V. By drawing a vertical line on spontaneous potential SSP that a sand would have. Alpha values from nearby wells can be used to cut-off from a gamma ray log is described in Figure In the above example in Fig.

The procedure for obtaining a clean carbonate zones. At interval transit time II. In this interval of analysis are crossplotted. The gamma ray log can be used to map clean shale-free sandstones or carbonates versus shaly sandstones and To date.

An important contribution to subsurface analysis of Next. The geologist can identify and map the clean carbonate or equation for SSP is: Asquith Council Grove 1. Clusters for the three can be used to determine lithology when a limited number carbonate rock types oolite grainstone. Where lithology is more complex.

The open circles represent data from a well essential first step to firmly establish the rock-type cluster without petrographic analysis. The carbonate rock types and used in the crossplots.

This is very important in subsurface facies mapping and depositional environment of wells without petrographic because of the difficulty in obtaining cores and cuttings analysis can then be determined by the cluster in which each from every well in an area. Crossplotting of multiple log reponses can be used to The advantage of log crossplot techniques is that they establish relationships between log responses and rock maximize use of available information.

Cores and cuttings types. Figure 53 is a facies map of the Council Grove 3. The carbonate rock type wells. Poroui Microcrystallino Dolomito. GR a N on—Porous. Microcrystollino Limostono. See Chapters IVand Vabout log interpretation.

After Asquith Note in log tracks 2 and 3 that the neutron log is represented by a dashed line and the density log is represented by a solid line see Chapter IV. The gamma ray log is in track 1 see Chapter V. This crossplot helps to determine lithology. Note how data points are clustered within a lithology triangle bounded by three corners: In this case, the rock is identified as anhydritic limey dolomite see text.

Note that two points plot above the limestone-dolomite line, and into the zone of secondary porosity. Note that the data points cluster in a triangle defined by the end-members—limestone. By formula.

In this example a75 is the thinner of the two. From this log-depth scale you can count depth-increments to determine alpha thickness. From the intersections. Two different cutoffs are demonstrated: You must first determine SSP see text for formula. Determining Alpha a from an SP log. In this exercise. Plot a scale of lOOmv on the SP log. Draw a vertical line from the scale value of 20 API units and determine the thickness and limits of the clean carbonate formation bioherm much as you determined alpha values in Figure Example gamma ray log depicting a 20 API unit gamma ray cutoff used to determine a clean carbonate interval.

Determine gamma ray cutoff see log. Roosevelt County. Example isopach map of clean carbonates from the Mississippian Mission Canyon Formation. This comparison of log response to facies helps the geologist develop rock type clusters.

Solid squares and circles represent wells with core or cuttings available. Example crossplot of formation resistivity Rt. Open circles represent wells with log control only. Ochiltree County. As with Figure Example crossplot of formation resistivity R. Solid black circles represent wells with only log control. The legend defines the position of core. Formulas Used for Calculating geologic ages.

Whenever this happens. Memorizing log patterns and curve values just not be asked to solve them. Although all the case studies are based on actual field Where: A pipe-setting decision barrels STB doesn't always require a full-blown log analysis. A derivation of variables is included actual experience with logs. That's I. The ones presented here cover a variety of geographical areas.

In the first example the reader is asked to do very tank barrel little. Sw expertise. These Volumetric Producible Hydrocarbon Reserves are not necessarily a classic representation of any of the variations.

The learning process is slow. There are absolutely no in this listing. Most geologists use formula I. No matter how significant log interpretation is to a Formula II.

This information indicates that the Where: The slower depth drilling times may mean that the sandstone doesn 't have the Where: Total gas background on the. The primary target. Rule of thumb for static bottom hole pressure: You have the following information: Moveable Oil Saturation: It should be used only in crossplots where you are trying to determine the relative permeabilities: Five depths were selected for your convenience and are listed in the table.

Residual Oil Saturation—Sxo is water saturation of You may find this list of formulas helpful as you pursue flushed zone calculated by: Water Saturation Archie—Hers. Work Tabic: High resistivities on resistivity logs in tracks 2 and 3. Permian basin. Values from this log are used in work Table A.

Pennsylvanian Atoka Sandstone. Hydrocarbon suppression of SP log in track 1 solid line. At a depth of Gamma ray log track 1 dashed line has lower gamma ray count in Atoka Sandstone interval because sands have lower radioactivity than shales. Mudcake is indicated because the hole diameter. Valuesfromthis log are used in work Table A. Strong gas effect. From a depth of Mudcake on caliper log in track 1 dashed line. Shading in track 2 indicates separation between wet resistivity R.

The greater the separation. These low values also indicate that various permeability crossplots. In this When this occurs. The values forms by the accumulation of solid particles from drilling are greater than 0. Log interpretation information permeability to gas Krg means there is a correspondingly especially significant to your decision is: On this is initially puzzling because.

Mudcake calculation of the moveable hydrocarbon index. The data points cluster along a acres. This high residual gas saturation is the result of medium-grained to coarse-grained is shown on the plot. The well's first year cumulative expected that hydrocarbons would be moved out instead of production was 3. This is anomalous because other evidence supports square inch PSI and a high initial bottom hole pressure the conclusion that the reservoir has high porosity and IBHP of 5.

Chapter VI. The calculated absolute open flow CAOF was saturation. This mudcake development is Additional anomalous information comes from the important because it indicates a permeable zone. Atoka Sandstone provides the following information. While you believe the well contains a at irreducible water saturation. The high relative decision to set pipe. To dc gas saturation remember: Such suppression suggests the presence of that most of the hydrocarbons will remain in place in the hydrocarbons.

Another crossplot in Figure The density log moveability should not be ignored in initial log evaluation. Because water saturation gas-filled Atoka Sandstone reservoir. Atoka Sandstone. This supports sample cutting examination which indicates a The high residual gas saturation left behind after invasion medium-grained to coarse-grained sandstone.

Analyses of ROS. Their clustering also supports the conclusion that the The Atoka Sandstone was perforated from The reservoir. The gas gravity was 0. Other evidence that the reservoir is at irreducible water An estimation of Atoka Sandstone gas recovery of The SP log Fig. Remember that water saturation Archie Swa is equal to Swirr in zones at irreducible water saturation.

Remember that water saturation Archie Swa is equal to Sw jrr in zones at irreducible water saturation. Irreducible water saturation Sw irr t versus water saturation S w tt crossplot for determining relative permeability to gas Krg. Data points cluster along the 0. Values calculated for Swirr by this formula should only be used in crossplots to determine relative permeabilities: C stands for bulk volume water. Sw is equal to water saturation Archie Swa.

Fill in the rest of the table as you which is the matrix density for dolomite Table 7. As drilling proceeds. The formula for none were successful. Your company Parameters used in your calculations of recoverable oil are: In order to establish an Rg line in the Pickett crossplot. Twenty-five feet of oil-stained. The well has just penetrated the Devonian Duperow. Several paper. After coring. Values from the log Fig. If the fish the stuck DST tool is successfully removed from the hole.

After determining values for the different log parameters. Mississippian Mission Canyon Formation. Thermometer Broke RM at m e a s. Williston basin. From a depth of 9. The separation of the three resistivity logs which read the following resistivities: Combination Neutron-Density Log with gamma ray log and caliper. The high porosities on the neutron and density logs tracks 2 and 3.

The neutron log reads higher porosity than the density log indicating the lithology is dolomite tracks 2 and 3. The increased amount of correction on the bulk density correction curve Ap. Williston basin.. This increase on the correction curve may indicate the presence of fractures in the Mission Canyon tracks 2 and 3. Density log with F curve. Sonic log with gamma ray log and caliper.

The numerous porosity zones indicated by the increasing interval transit time At on tracks 2 and 3. Pass-one is used as a check of the computer's input of logging parameters before the pass-two log is generated Fig.

The higher water saturations over this interval. 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.

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. Three resistivity devices are greater than the resistivity of the formation water R, for needed to measure a transitional profile; these three devices freshwater muds, and where Rmf is approximately equal to measure resistivities of the flushed, transition, and Rwfor saltwater muds.

A hydrocarbon zone invaded with uninvaded zones Rxo, Rj, and Rt; see Fig. By using freshwater mud results in a resistivity profile where the these three resistivity measurements, the deep reading shallow R xo , medium Rj , and deep Rt resistivity tools resistivity tool can be corrected to a more accurate value of all record high resistivities Fig.

In some instances, the true resistivity R t , and the depth of invasion can be deep resistivity will be higher than the medium resistivity. Two modern resistivity devices which use these When this happens, it is called the annulus effect. 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 annulus profile is detected only by an induction log run soon after a well is Basic Information Needed in Log Interpretation drilled. Porosity logs The formation temperature is also calculated Asquith, require a lithology or a matrix constant before a zone's by using the linear regression equation: porosity 0 can be calculated.