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Log interpretation slidepack
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- 11. CALIPER LOG Uses ofCaliper logs: 1.Contributory information for lithological assessment – shaly formation can be very unstable. 2.Calculation of mud cake thickness, hmc = (dbit – dh)/2, where h stands for the hole, in inches. 3.Measurement of borehole volume, Vh = (dh 2 / 2)+1.2%, in litres per metre (L/m) 4.Measurement of required cement volume, Vcement = 0.5 x (dh 2 – d2 casing) + 1%, in litres per metre (L/m). 5.Indication of hole quality for the assessment of the likely quality of other logs whose data quality is degraded by holes that are out of gauge. Log data can often be corrected for bad hole conditions using the caliper readings, but the larger the correction, the less reliable the final data will be. 6.Selection of consolidated formations for wireline formation pressure tests, recovery of fluid samples, for packer seating for well testing purposes, and for determining casing shoe setting depths.
- 12. CALIPER LOG Caliper LogInterpretation Matrix
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Editor's Notes
- #5 SS – sandstone; lms – limestone; dolo - dolomite
- #7 •Gas is more resistant to electric current than water – oil is in-between but closer to gas than water because it is a hydrocarbon. •Flushed zone refers to the areas along the well depth that has been penetrated by the mud filterate •Univaded invaded zone refers to areas within the wellbore (along the wellpath) that has not been penetrated and contaminated by mud filtrates.
- #8 Where: Sxo – flushed zone saturaton; ρmf – density of the mud filtrate; ρf – true fluid density; ρh – hydrocarbon fluid density.
- #9 SP Logs: 1.It’s a lithology logging tool like the GR 2.Utilizes the principle of electricity like the resistivity tool/logs: 3.One of the oldest forms of logging measurements (since 1931) 4.SP logs are depth dependent – they are more accurate at deeper intervals 5.SP logs are known to respond poorly in limestone formations 6.SP logs are known to respond poorly in oil based muds (OBM) 7.Very good response in sandstone formations. Ions flow easier in permeable sandstones
- #10 1.It’s a lithology logging tool like the SP log 2.Measures natural radioactivity (potassium – k, Uranium – U; Thorium – Th) which are abundant in shales, and less in sand stones. 3.Uses the Geiger counter (scintilometer) for measurements 4.Unaffected by fluid content 5.API units are the relative standard of measurement (GAPI)
- #11 It is used to differentiate the exact mineral content of the lithology. It determines the element that emitted the gammarays by the energy of the gammarays, since the energy of the gamma rays depends on its source. Potassium gives off only a gamma ray, while the other elements give off a gamma ray and because they are still radioactive – they decay to other elements called daughters. These give rise to a pattern of gamma ray energies as unique as finger prints. They can help with clay typing. Variations of the relative amounts of potassium, thorium, and uranium are associated with specific shale minerals. As is so often the case in log analysis, crossplots are used to highlight these differences.
- #12 Used to measure hole diameter along it’s depth and formation stability Usually measures mechanically but a few uses sonic (accoustic/sound) devices. Since wellbore shapes are usually irregular, a tool that can measure several locations along the wellbore wall is often used. This device is called a multifinger caliper. Sometimes a simple two arms caliper tool can be used. Drilling Engineers use this log to understand the condition of the wellbore and the effectiveness of the mud system – since drilling muds are used primarily to maintain wellbore stability. A good indicator of good permeability and porosity zones in the reservoir rock (which can be verified with the GR or SP log), since a stable wellbore is indicative of a welll developed mud cake. Thus it can be used for lithology assessment – shaly formation can be very unstable
- #13 On Gauge: Formation is consolidated; Not pearmeable (Possible lithologies; Metamorphic rocks, Igneaous rocks, etc.). Larger than the bit size: Formation is weak or caved-in etc. (possible lithologies; salt formations especially if drilled with fresh washed; unconsolidated sands/brittle shales. Smaller than the bit: Means the formation is swelling into the wellbore; more mud cake development from porous and permeable formation. Mud cakes are deposited on the well wall as wellbore fluid flows through the porous and permeable formations (Possible lithologies; swelling or reactive shales; porous/permeable formations
- #14 Porrosity Cross plot is plot of two porosity logs (normally neutron and density porosity logs) in a certain fluid – usually fresh water (e.g. borehole filled with water or water based muds), governed by a set of equations. Results are dependent on lithology and is judged to be more reiable than a single porosity log. Response lines can also change with tool type
- #15 There are other common porosity cross plots such as: Sonic-neutron Sonic-density etc. All have complicating effects on; Shaliness Hydrocarbons (gas); Fractures. However the NEUTRON-DENSITY CROSSPLOTS are Most frequently used.
- #16 A single log created by splicing together two logs of the same type run at different times in the well; or by splicing two different types of log run at the same time. For example, it is common practice to splice all the basic logs (e.g. GE, Res, Neutron & Density) run over different depth intervals in a well to obtain a single composite record.
- #19 One of the easiest ways to obtain hydrogen is to get it from water, H2O. This method employs electrolysis, which breaks water into hydrogen and oxygen gas Hydrogen can also be produced from fossil fuels by steam reforming or partial oxidation of methane and coal gasification.