Rock Porosity Can Be Obtained From:Laboratory MeasurementsORPorosity Logs: Sonic, Neutron, Density

Also, EPT & NMREach Tool Measures a Physical Property.No tool Measures Porosity Directly, But Porosity Tool Response Depends On;Porosity, Saturating Fluid(s) and Matrix.

Porosity Logs

Sonic Log

Neutron Logs

Density Logs

EPT Logs

NMR Logs

Porosity Logs Crossplots

Sonic Log Is Simply a Recording Versus Depth of Sound Wave Travel Time Traverse 1 ft Formation. Known as Interval Transit Time Dt in micro-sec /ft, it is the Reciprocal of Sound Wave Velocity.Principle: Sound Waves Emitted From the Transmitter Are Governed by Different Acoustic Medium Includes Formation, Bore Hole Fluid Column and Tool Itself and Casing Conditions (in Cased Hole Logs).Equipments:There are Three Sonic ToolsBore Compensated Sonic tool (BHC)Long Spaced Sonic Tool (LSS)Array Sonic Tool (AST)

Porosity DeterminationSound Travel Time ∆tc (Compressional wave) depends on Porosity, Saturating Fluids and Matrix.Clean Formation∆tl = φs ∆tf + (1- φs) ∆tmφs = ( ∆tl - ∆tm) / (∆tf - ∆tm)

18943.547.551-56∆tc , µs/ft

WaterDolomiteLimestoneSandstoneLithology

Sonic Porosity Is Primary Intergranular Porosity, so in Vuggy Carbonate Rock, φs is Less Than φt (Density Porosity) by φsecφsec = φt - φs Shaly FormationsSonic Porosity Needs Shale Correction∆tl = φsc∆tf + (1- φsc- Vsh) ∆tm + (Vsh * ∆tsh)φsc= (∆tl - ∆tm) /(∆tf - ∆tm) - (∆tsh- ∆tm)/(∆tf - ∆tm)* Vsh

Shear Wave InterpretationShear Wave Transit Time Data Are Useful in Identifying Matrix Mineral and Pore fluids Nature.

350769086∆tsh , µs/ft

WaterDolomiteLimestoneSandstoneLithology

Density Logs are Primary Used as Porosity Logs. Other Uses Include Mineral Identification, Gas Detection, Shaly Formations Evaluation and Rock Mechanical Properties. PrinciplesA Radioactive Source, Applied to the Borehole Wall in a ShieldedSidewall Skid, emits Medium-Energy GR Rays into the Formation. These GR Rays Collide with the Formation Electrons, GR Loses itsEnergy. The No. of These Compton Scattering Collisions of GR IS Related to the Formation Electron Density, ρe.Electron Density is Related to Bulk Density, ρb

ρe = (ρb x 2Z / A)Z = Atomic number & A = Atomic weigh

There are Two Density ToolsFormation Density Tool, FDC Gives ρbLitho-Density Tool, LDT Gives Pe & ρb

Density Log PresentationPorosity DeterminationClean FormationFor clean formation bulk density depends on fluid density, porosity and matrix density.ρb = φD ρf + (1- φD ) ρmφD = (ρm - ρb) / (ρm - ρf)In Density Porosity Equation, Fluid Density, ρf is taken as one Assuming Water. If there is mud filtrate Near Borehole, ρf is > one, Then φD needs correctionsIf There is HC near Borehole, ρf is < one Then φD Needs CorrectionsShaly FormationPorosity Equation Becomesρb = φDC ρf + (1- φDC - Vsh ) ρm + Vsh ρshDensity Porosity Equation BecomesφDC = (ρm - ρb)/(ρm - ρf) - Vsh(ρm - ρsh)/(ρm - ρf)φD > φDC If ρsh < ρm & φD < φDC If ρsh > ρm

φD = φDC If ρsh = ρm

Neutron Logs are Primary used for Delineation of Porous Formation and Porosity Determination. Neutron Logs Respond Primary to Hydrogen Concentration in the Formation. Neutron Porosity is Liquid Filled Porosity.Gas zones can be identified by Comparing Neutron Porosity with Other Porosity Logs. Neutron Logs Can run in Open/Cased Hole

PrinciplesNeutrons are electrically Neutral Particles,

having the same mass of Hydrogen. 16 Cuire AmBe Radioactive Source Emittes Fast Energy Neutron and Collide with Nuclei of the Formation. Maximum Energy loss When Neutron Collide with Equal Masses Nucleus. At the End Neutron are Captured By the Nuclei of Atoms Such As Chlorine, Hydrogen Or SiliconThe Capturing Nucleus Becomes Intensely

Excited and Emitted a High Energy GR. Neutron May Be Recorded Either As The Number of GR OR The Captured Neutron Themselves.

Neutron Log Tools

GNT Non-Directional Device

SNP, Epithermal Tool, It is Good in Empty hole, Open Hole Tool

CNL Mandrel–Type Tool, Liquid Filled Cased /Open Hole, Not For Gas Filled Holes

Neutron Logs InvestigationsClean FormationCNL OR SNP Logs are Normally Calibrated to Limestone Base OR Sandstone Base.Neutron Porosity, φn is Formation Porosity if the Lithology the Same as for Calibration. If Not, Neutron Porosity, fn Needs Lithology Corrections.Shaly Formationφnc = φn - Vsh * φnsh fnsh is Neutron Response Against ShaleGas FormationNeutron Porosity in Gas Formation is much Less Than in Water OR oil Formation. Hydrogen Indexes are close in Oil & Water While Hydrogen Concentration in Gas is Considerably Lower. So Combination of Neutron with Density Logs is Good For Gas Zones Identification.

Sonic, Density and Neutron Logs Respond to Lithology as well as Porosity.Lithology Changes from Foot to FootAn Approach is to Run Two OR Three Porosity Logs. By Comparison of Porosity Logs, Obtain Good Indications of Lithology Contents.Dual Porosity CrossplotsDensity-Neutron CrossplotDensity – Acoustic Crossplot Neutron- Sonic Crossplot

Tri- Porosity Crossplot

M-N CROSSPLOT

M = [(∆tf – ∆tl) /(ρl – ρf) ] * 0.01N = (φNf – φNl) /(ρl-ρf)

From M-N Crossplot, Obtain Information on Three Components on Lithology.

M-D CROSSPLOT

This Crossplot is Mainly Designed to Identify Rock Matrix