“The detail of the porosity evaluation and also the equality of numerous heart to log comparisons indicate a high level of certainty at the appraised total porosity (por). Core firms frequently use of the expression”effective porosity” to imply these exact same oven dried helium interconnected pores that makes a scenario where the exact same dimension has two distinct names. However’interconnected’ isn’t the mainstream petrophysical definition of’powerful’ porosity and also the confusion about overall vs. effective porosity is because of this longstanding inconsistency between heart businesses use of the expression”successful porosity” to imply interconnected pores blindsided by He participates from the lab mainstream petrophysicists (Shell, Archie, W&S, NMR literature, and this report) to imply (total porosity — clay bound water) after Hill, Shirley and Klein’s historical connection between laboratory measured Qv along with CBW volume. Hence the exact same dimension value is known as”complete” by mainstream petrophysicists and”successful” by several heart businesses. Herein lies the origin of the disorder.
How do a pair of these plausible, scientifically curious folk get so confused? The term effective porosity can also be used loosely by other people at an intuitive common sense and generally qualitative manner, as shown below. Note additionally that non-NMR standard logs lack the basic information by which to ascertain a storage capability”powerful” porosity from stones comprising non-clay micro-pores like carbonates or walnut silts. Non-NMR log established determinations of”powerful” porosity in clay and so CBW complimentary micro-porous carbonates are mostly meaningless — what application is supplying the data for storage capability? When studying a fresh carbonates petrophysical report and also the word effective porosity is utilized ask yourself how that amount was quantified. This is the principal reason carbonates (reservoirs in which compaction and clays don’t restrain storage capacity and permeability) have been regarded as hard to assess with traditional logs, since no log information is available to quantify storage capability — the benefit of NMR from carbonates.
This writer participates with mainstream petrophysics and utilizes”complete porosity” to equate to the fundamental volumetric mention of traditional, sexy oven dried heart to constant weight (c.100degC) porosities, like those plugs dried into 115degC. Reviewers should look for the center report for the important words”oven dried to constant weight” to find out whether the core reference dimension is complete porosity — roughly 80 percent of heart investigation globally is. In circumstances of humidity drying (generally 60C 40RH) the test should nevertheless be calibrated to this center porosity but SCAL have to possess this exact same dimension as its foundation or the test becomes more”disintegrated petrophysics”. Conventional heart, special logs and core have to be equivalent. Logs only carry the center dimensions along the nicely track, like freight trains.
Under extremely rare cases (pers. Comm Dave Bowen) traditional core oven helium dried porosities don’t report all of the pore area, in which pores are now closed off as in intra crystalline pores. The vital purpose for the petrophysicist here is the correct utilization of this center reported grain density at the fixed stage fluid density process herein will nevertheless allow logs to replicate the center measured porosity’s by virtue of the cores reduced grain density — we still need a straight measured benchmark. The key issue is if logs are calibrated into some parameter that’s directly measured and precise.
Among many reasons for embracing total porosity is the association between shale quantity and Ro could be viewed. In effective porosity tests the analyst is refused this advice because the porosity parameter vanishes in shales, denying that the petrophysicist strong, instant advice for shaly sand tests. In case the petrophysicist wishes to know tool answers — that react to the total formation not pieces of it — through the petrophysical investigations shale porosity should not be concealed from view and Sw should not be truncated at 1.00. If your customers favor the makeup of effective porosity show it as soon as you’ve completed the evaluation and knew what’s actually occurring.
Core porosity measurements generally give complete porosity. E&P supervisors will need to understand something different. They want estimates of prospective reservoir depth,’powerful’ porosity, permeability as well as the quantities of producible hydrocarbon and water.
‘Complete’ and’powerful’ porosity are equivalent in non-shaly reservoirs, and might be almost equal in shaly sandstones containing clays (aside from smectites) with small clay-bound water from the clay structure. Immature smectite shales with’heart’ and’complete’ porosities of 23 percent are impermeable non-reservoir stone.
To acquire practical outcome, petrophysicists and log analysts surely will need to understand and appraise’complete’ porosity as well as the quantities of water jump in clays. But for its end users of their petrophysics training results it’s more enlightening to be offered with’successful’ porosity. It reduces confusion and provide a more sensible test of the reservoir. In thickness plots of the outcomes,’complete’ porosity ought to be de-emphasised and’successful’ porosity highlighted”