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Occasional interesting posts by Dr Mark



Your NMR log is a BVW-Height log – a Saturation-Height log

NMR and Swi

Assuming the Bound Fluid Volume (BFV) T2cut of 33ms clastics or 100ms carbonates is reasonable what does BFV/Port = ?

Swi, right? So we just need to know we are above Top Transition Zone (TTZ) to know Sw. Best to plot a total porosity bulk volumes results track with excess pressure ( – aquifer press) to understand what’s happening in your porosity – hint: don’t plot saturations, plot volumes)

NMR and Swht

Remember you’ve heard people say that the T2 axis can be converted to a Pc axis? What does that mean?

It means that every T2 value has a corresponding height above FWL for which the faster T2 pore volume remains water filled. Logging contractors chop up the T2 axis into porosity bins e.g. Schl CBP1 thru CBP8, so always get those in your wellsite LAS file, please!

Now, the key. Each T2 bin represents a pore volume which will remain water filled until height reaches its slower T2 boundary height, then that bin will de-water with height. The excess pressure (capillary pressure, height) of the HC needs to push hard enough to remove the water and fill that pore volume. Don’t worry about the HC’s NMR properties – an oft repeated red herring – keep focused on the water volume.

A BVW-Ht display

Let’s plot CBP1 thru CBP8 on top of each other (cumulative) so they build up to total porosity and shade them red-yellow-grey-black with decreasing T2, which is increasing Pc and height. Now we have a BVW-Height log which shows us what pore volume will remain water filled at every height, right? From that we calculate our Sw-ht log. This saturation height log is far more information rich than the standard reservoir engineering poro-perm crossplot regression to Swht (J function, Lambda etc), driven by porosity.

But what about the T2 to Height conversion?

We can do SCAL (NMR-Sw-Pc) lab work if we want to pay, core, wait and worry about lab to reservoir. My preference is always to ask the question: “Where in my reservoir do I know the answer to the question I am asking?” Where do I have NMR, a reasonably certain BVW or Sw log and know the FWL?  Do this while you wait for SCAL, during operations maybe. I can do that for you!

The NMR BVW-Ht log captures the power of magnetic resonance logging and transforms it into something we actually want and it does that every 15cm. Can we afford to ignore this information?

For a fuller explanation come see    OR

Let me know if I can help with anything in this post or petrophysical support generally

Enjoy Petrophysics!

#petrophysics #spwla #saturation #saturationheight #core #loganal #logging #oil #reservoir

#reservoirengineer #reservoirengineering #reservoirsimulation #shalysands #carbonates




Never Plot Sw 0 – 1 !

Log analysis modules truncate Sw at 1.00. This destroys information which you should use to check your evaluation.

What’s so good about water zones?

We know Sw can’t exceed 1.00 so if your evaluation calculates that it does, its wrong. Don’t apply SCAL and/or core if you know something is wrong, think.  Instead mark out Sw100 zones which really are at 100% Sw. Then think of these as downhole labs for log analysis, the best labs you can get at reservoir temperature and pressure and using the tools and scales of measurement you actually use, unlike core.

Assuming we have the same Rw and rocktype (m) in our downhole lab we must now ensure our Sw reports 1.00 as lithology varies, if it doesn’t its wrong we need this end point to be correct  (Point 3/4 calibrations for HPV, see IPRC)

How do we do that?

Easy, set Archie Sw to 1.00, back calculate m apparent (ma) or Rw and call it Rwa. We’ll use ma here. Now all we need to do is predict it. In Tertiary clastics we can use multiple linear regression with por and vsh to get ma predicted, and call it mv. You can do this in 5 minutes, no core, no waiting, no cost. Now, with mv, we know Archie will predict the correct Ro and that Sw will =1 in water zones, shaly or clean.  We also know mv will deliver the correct Ro above the FWL because we have the same Rw and rock type (m) and Archie Ro is only a function a*Rw*por^m. Isn’t that what shaly sand equations do, predict Ro correctly in shaly zones? Yes. We just did that.

But what about n?

n is more difficult because we don’t have a reference Sw. If we do, say Sw, OBM core, dielectric, NMR, chart k-4 etc we can use these – but cautiously – and back calculate n. If we don’t let n = mv or maty be use SCAL n if our plugs are shaly or just leave n=1.9. It won’t be too bad or too controversial for our audience to accept. Our main driver is m.

Do this and you have a quick, fast and reasonably correct Sw and can show your audience that Sw actually does = 1 in shaly water, something SCAL evaluations may not do.

Extra bit..

Because ma is a compound term which bundles the clean “intrinsic’ pore geometry m and the shaly sand excess conductivity BQv into one number, ma, we can deconvolve ma by letting the clean, intrinsic m* = 1.90, or 2.00, it’s not critical.  Deconvolving ma into m* and BQv allows us to use Waxman Smits proper, is simple to understand, very quick and actually works. It is similar to Juhasz’s Normalized Qvn but uses ma instead of Rwa. Juhasz chose Rwa because it adheres more closely to Waxman Smits’ Cwe concept (which he wanted to make log based).

All this from plotting Sw 0 to 1.25 !

I have used these methods along with full scale WaxmanSmits and DWM in countless reservoir studies and written them into my “vault” command file. They work. They are simple, quick and easy to understand and are explained more fully and interactively my courses, especially IPLAM and IPRC

Enjoy Petrophysics!

#petrophysics #spwla #saturation #saturationheight #core #loganal #logging #oil #reservoir

#reservoirengineer #reservoirengineering #reservoirsimulation #shalysands #carbonates



** Warning **

Please note that plagiarised copies of my “Integrated Petrophysics..” course titles and descriptions appear on the internet and Linkedin e.g.

The genuine versions of IPRC – Integrated Petrophysics for Reservoir Characterisation; IPCFR – Integrated Petrophysics for Carbonate and Fracture Reservoirs and other “Integrated Petrophysics..” courses (IPQL, IPSWHT, IPLAM, IPSCAL, IPPetroDB) have been developed and presented by myself over 25+ years and are available only through myself, HOT Engineering or occasionally bona-fide 3rd parties. These courses and content are not available through any agents if my name is not clearly stated as Course Instructor, despite the course title and description being verbatim copies of the originals, available at

Before paying money for “Integrated Petrophysics” courses I suggest you first contact myself or HOT Engineering directly to establish if you are actually buying the course you assume you are buying or an imitation which does not provide the same instructor or content as the original “Integrated Petrophysics..” courses.

Why are these courses being imitated?

The original “Integrated Petrophysics…” courses given to over 3,000 attendees have earned a decades long reputation as powerful, real-world petrophysical training, frequently achieving the “Best course attended” accolade

Early versions of these courses were first given in 1990 and have evolved over 30 years of consulting and course feedback. They are required learning for petrophysicists by many energy companies and are repeat inhouse training courses with major multinationals. The course content is registered copyrighted and Intellectual Property of myself.

Enjoy Petrophysics!

#petrophysics #logging #core #saturation #reservoirengineering #reservoirengineer #spwla




Capillary Pressure Saturation Height Functions

Is there anything else which controls saturation in an initial conditions hydrocarbon reservoir or can we just assume this is the whole story?

  • What if our saturation height function is derived from SCAL plugs which deliberately avoid vugs in our vuggy carbonate – the normal situation?
  • What if the matrix encasing the vugs actually is NOT breached by the reservoir capillary pressure (height) in our reservoir but our vugs are oil filled? Why are we even using a saturation height function?
  • Do the tricky inputs we have assumed in our SCAL petrophysical Swht model (IFT, Theta) create more error in HPV than using an NMR BVW or elemental spectral GR Carbon Log?
  • Have we evaluated HPV from at least two rival methods and/or data, reconcilled the results and improved our base case by applying what we found? A “multistream” approach
  • Wait… is the porosity that drives our height function with logs identical to our SCAL & RCA porosity or are we still confused about total and effective porosity? (Sort this out!)
  • Are we just doing what everyone else does or are we thinking from first principles about how best to achieve our objective from the data we have? Actually, what is our objective anyway? Sw, HPV or something else?

Come see Vienna 8-19 May 2023

IPRC  Integrated Petrophysics for Reservoir Characterisation


IPCFR Integrated Petrophysics for Carbonate & Fractured Reservoirs – A Roadmap


Enjoy Petrophysics!

#petrophysics #saturation #reservoir #reservoirengineering #reservoirsimulation #logging #core #spwla



n is a hydrocarbon zone log analysis parameter

The function of n is to translate a rise in (logged Rt / log predicted Ro) above 1.00 into the corresponding reduction in reservoir Sw below 1.00

Sw^-n  = Rt / Ro


Different scales of measurement between SCAL n and logged Rt invalidate SCAL n in heterogeneous reservoir.


n is an internal log analysis parameter. If SCAL n fails to create actual reservoir Sw from logged Rt/Ro, then the n we are using is wrong, period. It doesn’t matter what lab n is.


What do we use?


Ask yourself: “Where in the reservoir is the answer to the question I am asking?” So, where are we reasonably certain of Sw?  Perhaps we have rotary sidewall cored zones with known por, k and height from which we can calculate a J value and estimate Sw?  Then, use whatever n value makes your logged Rt/Ro deliver that reservoir Sw.  It may be an n value you have never seen in the lab, so what? If you don’t use it your log analysis is wrong.


Think don’t follow. Our task is to evaluate the real reservoir with the tools we are given.

Hint: is each input of the saturation equation a measurement taken from exactly the same piece of of reservoir rock? No, it never is in log analysis.  Hence log analysis works well when the rock is homogenous because it doesn’t matter at what scale or location you measure it.

Enjoy Petrophysics!

#petrophysics #logging #core #saturation #reservoirengineering #reservoirengineer #spwla




m is a water saturated internal log analysis parameter

The function of m is to create a predicted Ro which equals logged Rt if reservoir Sw=1

Different scales of measurement between SCAL m and logged Rt invalidate SCAL m in heterogeneous rock.

m is an INTERNAL log analysis parameter. If SCAL m fails to create LOGGED Sw=1 in Sw100zones of the same rock type, m is wrong, period.

So if Sw goes hard left onto 1.00 in water zones what does that tell you?

Hint: always plot Sw 1.25 – 0 until final results

Enjoy Petrophysics!

So what about n ?

#petrophysics #logging #core #saturation #reservoirengineering #reservoirengineer #spwla




Renewable Energy: The beginning of the end of the honeymoon period

Whilst a long term fan of the inevitability of renewables it is perhaps worth noting why we humans have been so in love with oil for the last 100 years: Energy Density.

This slide from REP shows just how deliciously energy dense oil is – something we have gravitated towards throughout history but are now recoiling from. Much maligned diesel, like most fossil fuels, is approx. x22 as dense by volume as a modern Li ion battery and x74 by weight.

Oil’s energy density doesn’t compare with nuclear of course, which is perhaps a more realistic alternative, but we have learnt to mine, pump and store energy in oil with an ease that we are far from achieving with the electricity from renewables.  Electricity is far more problematic to store in an energy dense form than oil; its energy (power) equivalent transmission lines are also hundreds of times more expensive to build, consume hundreds of times the critical minerals and land area and once built proceed to leak 3-7% of their energy per 1000km, even in ultra high 1,000,000 volt transmission lines (UHVDC, UHVAC). These are factors humanity will increasingly come to realise as the true cost of renewable energy. We can of course synthesise energy carriers locally at source as oil, ammonia or hydrogen, whose density becomes comparable with oil, but synthesis wastes energy itself and requires additional new infra structure – more mining and more transportation.

The honeymoon period of renewable energy is ending and although, as proclaimed above, I am big fan of the inevitability of renewable energy, I urge us all to be honest, transparent and practical and to ridicule political correctness regarding the challenges we face in replacing oil as our primary energy source.

REP     Renewable – Energy Primer


#energy #renewable_energy #energy_density #oil #gas #power #transmission #pipeline #petrophysics




Here’s grid level energy storage, just switch it on!

The uptake of cheap, clean RE is stymied by the lack of grid level storage. A solution for smoothing RE’s supply intermittency already exists, it just needs switching on. No impossible technical breakthroughs required.

The storage capacity of Australia’s distributed 23,000 EV is about 1,725,000 kWh. The storage capacity of the world’s largest centralised lithium ion grid storage, Hornsdale SA, is 194,000 kWh, 11% of Australia’s EVs and cost 172m AUD to install plus running costs, or 97 AUD per South Australia head. So, Australia EVs have about 9 times the storage capacity of the worlds largest lithium ion grid storage, its just not connected.

What we need:

– real time pricing of grid electricity embedded in the 50Hz outlet signal (or in a carrier wave. Grid frequency drops as load exceeds source due to increased turbine rotor torque)
– EV inverters which export user defined discharge to the grid as a function of grid price. Charge back when the grid is cheap
– media pressure and deregulation to clear the forces which are blocking this fix

Advantages: a better more effective use of existing resources; Democratisation of energy/energy autonomy (there’s the rub); Increasing EVs increasing grid stability; Energy security;  Flexible; Cheap; Getting cheaper; Lower taxes; Self regulating; No running costs; Neat and something for a country or a state to be proud of !

Ignorant media, institutions and politicians who don’t want to understand critical science and fail to serve their public.


#renewableenergy  #energystorage  #smartgrid  #evcharging